The 2009 abstracts are from Undergraduate Senior Honors Theses, Master's Theses, and PhD Dissertations completed at the University of Texas at Austin in the field of Geological Sciences. See the Geological Sciences Theses and Dissertations Index : 2009 - 2011 for a more concise listing of authors, titles, and supervisors. Dissertation abstracts published prior to 2001 may be found through Dissertations and Theses: Full Text.
VESICLE TEXTURES AND THEIR IMPLICATIONS FOR PROCESSES OCCURRING WITHIN A VOLCANIC CONDUIT : HRXCT ANALYSIS OF WHITE DACITE PUMICE FROM POPOCATÉPETL VOLCANO, MEXICO
Samantha Abbott, B.S.
University of Texas at Austin, May 2011
Supervisor: James Gardner
60 pages, 21 references, 5 tables
Vesicle textures have been used to interpret eruption intensity and conduit processes such as vesiculation, shear, and fragmentation (Gardner et al., 1996; Papale, 1999; Polacci et al., 2006), although the relationships linking pumice textures to vesiculation and fragmentation processes are not well understood. This project was a three-dimensional examination of large vesicle textures of pumice from the White Pumice plinian eruption of Popocatepetl Volcano, Mexico. The software package Blob3D was used to quantify vesicle sizes, shapes, and distributions of four samples of the white pumice from high-resolution X-ray computed tomography (HRXCT) scans. The relative orientations of vesicles and phenocrysts in the pumice were analyzed in the software package Quant3D. A bimodal vesicle size distribution was found in all of the pumice samples. Vesicles become increasingly deformed with increasing bulk vesicularity. The volume percent of large vesicles and their bubble number densities increase with increasing vesicularity. The vesicles and phenocrysts in all of the samples show preferred unidirectional or planar orientations, which are attributed to pre-fragmentation shear within the conduit during an eruption. The strongest vesicle and crystal orientations are seen in the highest vesicularity pumice. The presence of welded textures in two pumice samples is evidence for post-fragmentation evolution.
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WILL IRAQ ESCAPE THE RESOURCE CURSE?
Saya Ali Ahmed, M.A.
University of Texas at Austin, May 2011
Supervisor: James Gardner
62 pages, 37 references, 7 tables
Some oil-rich countries suffer from a resource curse, a paradoxical situation in which a country with oil wealth has poor economic growth and social development. A country can escape the resource curse by selecting appropriate policies. Governments are responsible for utilizing the right policies and managing the natural resource revenue effectively to benefit their nation.
In this report, various economic, political, and social measurements are used to examine the fall into the resource curse by Nigeria, Iraq, and Brazil for a period of time, and the scape of Norway from the resource curse. The report also evaluates the current circumstances of Iraq to determine which direction the resource curse will take. Several recommendations are presented to direct Iraq out of the resource curse.
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MINERALOGY AND GEOCHEMISTRY OF THE NON-SULFIDE ZN DEPOSITS IN THE SIERRA MOJADA DISTRICT, COAHUILA, MEXICO.
Hye In Ahn, MSGeoSci
University of Texas at Austin, August 2010
Supervisor: J. Richard Kyle
179 pages, 65 references, 10 tables
The Sierra Mojada district consists of multiple types of mineral concentrations ranging from polymetallic sulfide deposits, "non-sulfide Zn" (NSZ) deposits, and a Pb carbonate deposit hosted by Upper Jurassic to Lower Cretaceous carbonates. This study focuses on the two non-sulfide Zn deposits, the Smithsonite Manto and the Iron Oxide Manto, that occur south of the San Marcos fault. The Smithsonite Manto shows karst features, including internal sediments interbanded with smithsonite (ZnCO3). The Iron Oxide Manto consists of strata-bound zones dominantly of hemimorphite (Zn4Si2O7 (OH)2•H2O) that fills pores in Fe-oxides. The mineralogy of the NSZ mineralization consists of smithsonite, hemimorphite and Zn clays (sauconite) associated mainly with calcite and Mn-Fe-oxides. Zn clays are abundant in the Smithsonite Manto, but no Zn clays have been found in the Iron Oxide Manto. This project attempts to constrain the origin of the NSZ concentrations through petrographic and mineralogical study of major Zn-bearing minerals, and their carbon and oxygen stable isotopes and Pb isotope geochemistry.
Smithsonite in the Smithsonite Manto occurs as botryoidal aggregates consisting of scalenohedral or rhombohedral microcrystals and banded colloform or massive smithsonite in open spaces, whereas smithsonite in the Iron Oxide Manto occurs as rhombic microcrystals grown in pore spaces or finely intergrown with Fe-oxides. Both Fe-poor and Fe-rich smithsonite are found in the Iron Oxide Manto. Under optical-CL, smithsonite displays complex growth zoning that can be related to variable trace element content. Trace elements semiquantitatively analyzed using LA-ICP-MS show that most blue luminescent smithsonite has lower Mn contents than pink to bright red luminescent zones in smithsonite.
Preliminary fluid inclusion petrography in hemimorphite and calcite suggests that fluid composition can be related to precipitation of NSZ minerals from freshwater to slightly saline waters. Calculated salinities for two phase (liquid +vapor) and single phase (liquid) inclusions in hemimorphite range between 0.0 and 1.6 wt. % NaCl equivalent, and salinities of inclusions in calcite were between 0.0 and 1.1 wt. % NaCl equivalent.
The oxygen isotope values for smithsonite are relatively constant (avg. δ18OVSMOW = 21.9 ± 0.5‰), whereas δ13CVPDB values range from -8.4 to -1.1 ‰. The oxygen isotope values in late calcite are within the same range of smithsonite, whereas the average values of the carbon isotope are lower by 5 ‰. Formational temperature of smithsonite is calculated to be between 26 ~ 40 ºC using the modern groundwater composition at Cuatro Ciénegas. Similar Pb isotopic compositions of smithsonite and cerussite to galena suggest the source of metals in the NSZ deposits presumably originate from the sulfide deposits.
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CRANIODENTAL MORPHOLOGY OF THE RACCOON, PROCYON LOTOR, AND THE RELATIONSHIPS OF PROCYONIDAE
Heather Elizabeth Ahrens, M.S. Geo. Sci.
University of Texas at Austin, August 2010
Supervisor: Timothy B. Rowe
204 pages, 63 references, 5 tables
The northern raccoon, Procyon lotor, is an extant member of Carnivora, and one of the most recognizable North American mammals. Published discussions of the raccoon cover a variety of anatomical systems, including detailed work on the carotid arteries, auditory region, and dentition, as well as aspects of demographics, and evolutionary relationships. However, there has not been a comprehensive description of the craniodental morphology of the raccoon. I present the first bone-by-bone description of the skull of Procyon lotor with the aid of high-resolution X-ray computed tomographic data, which allows for detailed examination of the external and internal anatomy of the cranium. The paths of canals within the skull, such as the facial canal and transverse sinus, were traced without destruction of the specimen and are presented here. The suprameatal fossa, presence of the secondary common crus, absence of the subarcuate fossa, and morphologies of the palate, including the morphology of the nasal spine, are potentially informative phylogenetic characters described here.
The description of additional morphology of the raccoon is the first step towards identifying phylogenetically informative characters, evaluating the incongruence between phylogenetic analyses based morphology and molecular data, and assessing claims of adaptive convergence versus homology in Procyonidae. A new comprehensive craniodental analysis presented here yields new phylogenetic results regarding the ingroup relationships of Procyonidae. Though the characters used to unite and diagnose Procyonidae still have poorly understood homologies and taxonomic distribution among both Procyonidae and Musteloidea, there is significant morphological support for clades within Procyonidae. Within the ingroup, Bassariscus astutus is the least derived member of Procyonidae, Bassaricyon and Potos are recovered as sister taxa, Ailurus fulgens is recovered nested within the clade, and Procyon lotor is strongly united with the coatimundis (Nasuella plus Nasua). The amount of morphological support within the clade and the disparate topographical regions of the skull from which the characters are derived may indicate that these synapomorphies are the result of homology rather than adaptive convergence, as suggested by analyses based on molecular data.
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PATCH-REEF AND RAMP INTERIOR FACIES ARCHITECTURE OF THE EARLY ALBIAN MURAL LIMESTONE, SOUTHEASTERN ARIZONA
Rachel E. Aisner, M.S.Geo.Sci.
University of Texas at Austin, December 2010
Supervisor: Charles Kerans
161 pages, 74 references, 4 tables
The Mural Limestone, located in the Mule Mountains to the northeast and southeast of Bisbee, Arizona provides an exceptional outcrop analog for time-equivalent productive reservoirs in the Albian Glen Rose patch-reef play of the Maverick Basin. The Mural Limestone is exposed in a number of folds and east-dipping fault blocks in the Grassy Hill and Paul Spur localities in the Mule Mountains and represents a remnant of a south-facing distally-steepened carbonate ramp that prograded into the Chihuahua Trough in Albian time. This study documents the detailed facies architecture and sequence stratigraphic setting of a multicyclic patch-reef and its associated ramp interior facies at the Paul Spur and Grassy Hill localities, respectively.
Small mud-dominated coral-algal buildups (~5 m thick) and tabular biostromes (up to 1.5 m thick) consisting of rudist floatstones are common in the bedded ramp interior carbonates at the Grassy Hill locality in the Mule Mountains 10 km landward of the Paul Spur reef. Buildups in this area are flanked by weakly-cyclic and well-bedded skeletal mud- and grain-dominated packstones. At the Paul Spur locality, Mural facies consist of a 10-35 m thick patch-reef with four distinct reef communities: microbial-Microsolena framestone, algal-Actinastrea boundstone, branching coral-skeletal framestone and caprinid-requienid floatstone. Measured reef dimensions show a distinct windward-leeward margin with reef frame facies extending ~70 m from the margin and extensive leeward rudstone debris and grainstone shoal facies extending a distance of 870 m. Reef and backreef shoal facies exhibit low preserved porosity but petrographic analysis of backreef grainstones shows that primary porosity and permeability was present. These extensive reservoir-prone shoals may be a suitable reservoir target similar to flank rudstones and grainstones of the Maverick Basin reefs.
Three aggradational to retrogradational cycles of reef growth are evident at the Paul Spur locality. Retrogradational stacking is consistent with that of time-equivalent Lower Glen Rose patch-reefs in the Maverick Basin of Texas, which suggests a eustatic driver for stratigraphic architecture along the Bisbee/Comanche shelf. Backstepping of reef frame facies in Cycle 3 is interpreted to be time-equivalent to patch-reef development at the Grassy Hill locality.
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LITHOFACIES, DEPOSITIONAL ENVIRONMENT, BURIAL HISTORY AND CALCULATION OF ORGANIC RICHNESS FROM WIRELINE LOGS: A STUDY OF THE BARNETT SHALE IN THE DELAWARE BASIN, PECOS CO., WEST TEXAS, AND COMPARISON WITH THE BARNETT SHALE IN THE FORT WORTH BASIN.
Walaa Awaad Ali, M.A. Energy and Erath Resources
University of Texas at Austin, May 2009
Supervisor: William L. Fisher
210 pages, 89 references, 8 tables
Studies of core and logs from the Pioneer Reliance Triple Crown #1 (RTC#1) through the Barnett Shale in Pecos County in the southern part of the Delaware Basin, west Texas allow comparison of the lithofacies and depositional environment of the Mississippian section in this area with that in the Fort Worth Basin (FWB). Overall, mudrock facies are similar although, in contrast, the studied core contains no skeletal debris layers. Limestone concretions are absent, but there is substantial dolomite in many horizons. Total clay contents are broadly similar. There is more bioturbation than in the FWB. Agglutinated forams, Tasmanites, radiolarians, conodonts and echinoid spines are present. The depositional environment is a euxinic basin with a more distal setting than has been reported for the Barnett Shale in the FWB producing area. The transition zone between the Barnett Shale and the Woodford Formation is a chert rather than a carbonate, as reported in the northern part of the Delaware Basin in some locations and a mix of chert and lime in the rest of the basin. This transition zone is regionally referred to as the "Mississippian Limestone". Recognizing this, cross-sections and isopach maps for the transition zone between Barnett Shale and Woodford Formation have been constructed based on well-log correlations penetrating the Mississippian section in Pecos, Reeves, and Culberson counties. Additionally, core from the Hamon Regan #1 well has been examined to investigate the lithology and mineralogy for the transition zone and to interpret the origin of chert in the transition zone, between the Barnett Shale and Woodford Formation, and has been compared to the RTC#1 well in Pecos County. Moreover, gas content for the Barnett Shale interval has been estimated based on calculating the original TOC and original hydrocarbon potential. A published method to calculate organic richness from wireline logs has been tested for the Barnett Shale in the RTC#1 well and it gives fair correlation with measurements of TOC in cored samples. A 1-D burial history model was constructed for the Delaware Basin at the location of the RTC#1 well making use of vitrinite reflectance data from the Barnett Shale and Woodford Formation. Constructing the burial history is crucial for tracking likely diagenetic changes in the shale over time. These diagenetic changes in turn control hydrocarbon generation, overpressuring, natural fracturing, petrology and petrophysics, and present-day mechanical rock properties, all of which are important factors in determining whether production of gas from the Barnett Shale in the Delaware Basin will be economic.
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CONSTRAINING FRACTURE PERMEABILITY BY CHARACTERIZING FRACTURE SURFACE ROUGHNESS
Mishal Mansour Al-Johar, M.S.Geo.Sci.
University of Texas at Austin, December 2010
Supervisor: John M. Sharp, Jr.
193 pages, 69 references
Open and connected fractures, where present, control fluid flow and dominate solute transport. Flow through fractures has major implications for water resource management, underground waste repositories, contaminant remediation, and hydrocarbon exploitation. Complex fracture morphology makes it difficult to quantify and predict flow and transport accurately. The difficulty in usefully describing the complex morphology of a real fracture from a small 3-D volume or 2-D profile sample remains unresolved. Furthermore, even when complex fracture morphology is measured across three-dimensions, accurate prediction of discharge remains difficult. High resolution x-ray computed tomography (HXRCT) data collected for over 20 rock surfaces and fractures provide a useful dataset to study fracture morphology across scales of several orders of magnitude. Samples include fractured rock of varying lithology, including sandstone, volcanic tuffs and crystalline igneous and metamorphic rocks. Results suggest that the influence of grain size on surface roughness is not readily apparent due to other competing variables such as mechanics, skins and coatings, and weathering and erosion. Flow tests of HXRCT-scanned fractures provide real discharge data allowing the hydraulic aperture to be directly measured. Scale-invariant descriptions of surface roughness can produce constrained estimates of aperture variability and possibly yield better predictions of fluid flow through fractures. Often, a distinction is not made between the apparent and true fracture apertures for rough fractures measured on a 2-D topographic grid. I compare a variety of local aperture measurements, including the apparent aperture, two-dimensional circular tangential aperture, and three-dimensional spherical tangential aperture. The mechanical aperture, the arithmetic mean of the apparent local aperture, is always the largest aperture. The other aperture metrics vary in their ranking, but remain similar. Results suggest that it may not be necessary to differentiate between the apparent and true apertures. Rock fracture aperture is the predominant control on permeability, and surface roughness controls fracture aperture. A variety of surface roughness characterizations using statistical and fractal methods are compared. A combination of the root-mean-square roughness and the surface-to-footprint ratio are found to be the most useful descriptors of rock fracture roughness. Mated fracture surfaces are observed to have nearly identical characterizations of fracture surface roughness, suggesting that rock fractures can be sampled by using only one surface, resulting in a significantly easier sampling requirement. For mated fractures that have at least one point in contact, a maximum potential aperture can be constrained by reflecting and translating a single surface. The maximized aperture has a nearly perfect correlation with the RMS roughness of the surface. These results may allow better predictions of fracture permeability thereby providing a better understanding of subsurface fracture flow for applications to contaminant remediation and water and hydrocarbon management. Further research must address upscaling fracture morphology from hand samples to outcrops and characterizing entire fracture networks from samples of single fractures.
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COMPARISON OF REGULARIZATION TECHNIQUES FOR THE RECOVERY OF BLOCKY STRUCTURES
Adam Mark Allan, BS, Department of Geological Sciences
University of Texas at Austin, December 2009
Supervisor: Mrinal K. Sen
56 pages, 18 references
Acoustic impedance models of the Earth are inherently discontinuous, with sharp jumps separating layers with a velocity and/or density contrast. Any seismic inversion designed to recover acoustic impedance must faithfully reproduce these discontinuities from noisy seismograms. However, quadratic penalty terms and the band-limited nature of seismic wavelets smooth the solutions generated by current methods such as Tikhonov regularization, conjugate gradient least squares (CGLS), and total variation (TV) regularization.
Calvetti and Somersalo (2007) suggest a sequential iterative method for regularizing the inversion in a Bayesian framework [2]. This study applies the Gaussian hyperprior method from Calvetti and Somersalo, used in image processing, to a geophysical problem as a means to better reproduce the discontinuities in the model and bypass the smoothing generated by the band-limited wavelet. Solutions to the hyperprior method and, previously mentioned, current methods are generated for two synthetic seismograms created from the same geologic model and corrupted with 5% and 10% Gaussian white noise respectively.
The smoothing generated by the lack of high frequencies in the wavelet is clearly demonstrated in the Tikhonov regularization and CGLS results, while the missing low frequencies in the wavelet clearly inhibit the recovery of exact impedance magnitudes in the three current techniques. The Gaussian hyperprior solution shows great promise in its ability to recover the blockiness of the impedance solution despite the band-limited nature of the wavelet; however, the inversion stretches the first ~ 0.6 seconds of the solution resulting in a time shift of the interfaces after ~ 0.6 seconds of the log. Additional investigation must be conducted into the source and development of the time expansion before a complete comparison can be made.
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THE SEDIMENTOLOGY AND STRATIGRAPHY OF THE ARAB D RESERVOIR, QATIF FIELD
Mahmoud Hasan Alnazghah, MSGeoSci
University of Texas at Austin, August 2011
Supervisor: Charles Kerans
174 pages, 165 references, 3 tables
The Late Jurassic Arab D Formation in Saudi Arabia hosts the some of the world's largest hydrocarbon reservoirs including Ghawar, the world's largest oil field, and Khurais, the world's largest supergiant to come into production in the last 5 years. Despite the vast oil reserves within the Arab D, and the central role of this reservoir at Ghawar in making up short-falls in global production, our understanding of the much fundamental characterization work both in terms of modern sequence stratigraphic reservoir frameworks and linked structural/fracture characterization. This study of Arab D reservoir at Qatif, immediately to the north of Ghawar, provides one of the first looks at a modern sequence analysis of this producing interval and illustrates that porosity zonations, and ultimately flow unit architecture may be substantially different than currently in use. The Arab D of the Arabian Plate is a carbonate ramp system of exceedingly low angle (‹1°) developed during a low-eustatic-amplitude greenhouse Milankovitch setting.
Combined macroscopic and petrographic data analysis allowed recognition of nine depositional facies: 1) spiculitic wackestone, 2) Planolites-burrowed wackestone, 3) bioturbated skeletal-peloidal packstone, 4) pelletal packstone, 5) peloidal-skeletal grain dominated packstone, 6) peloidal-skeletal grainstone, 7) skeletal-ooids grainstone, 8) cryptalgal laminites and 9) anhydrite. The depositional facies defined are used to interpret three facies tracts from deep to shallow across the ramp profile: 1) low energy sub-storm wave base (SWB) dominated facies that may illustrate disaerobic tendencies, 2) high energy within-fair-weather-wave-base ramp-crest or mid-ramp facies including foreshore and upper shoreface oolitic and skeletal grainstones that define one of the key reservoir pay zones and 3) back-barrier tidal flats consisting of cryptalgal laminites, sabkha-type anhydrites, and salina-type anhydrites.
Three high frequency sequences are defined: QSEQ 1 is asymmetrical, dominated by subtidal lithofacies; and QSEQ 2 and QSEQ 3 are symmetrical and record a complex history of the fill on an intrashelf basin. Detailed cycle-scale correlations using core-based cycles and wireline log patterns allowed a cycle-scale correlation framework to be established that illustrates a north to south progradation of the Arab D reservoir strata, building landward from the Rimthan Arch.
Diagenetic features observed in the Arab D reservoir include fitted fabric (chemical compaction), dolomitization, and cementation. These features play a major role altering reservoir quality properties as they essentially control fluid flow pathways which ultimately alter primary porosity and permeability.
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HYDRATION AND TEXTURAL PATTERNS IN BALMORHEA BLUE AGATE
Martha C. Altobelli, BS, Department of Geological Sciences
University of Texas at Austin, May 2011
Supervisor: Mark Helper
78 pages, 36 references, 2 tables
Five agate specimens from near Balmorhea, Texas have similar patterns in mineralogical texture, cathodoluminescent (CL) response, and total hydration properties. Field investigations suggest the agates were derived from a single Tertiary trachyte lava flow in the Huelster Formation exposed in the low hills immediately north of Balmorhea Lake. Results of transmitted polarizing light microscopy, CL, and Fourier Transform Infrared (FTIR) spectroscopy support the idealized model of Wang and Merino (1995) for wall-banded agates. All show a decrease in total water content from agate rim to center. Texturally coarsely crystalline chalcedony and mega-quartz crystals have lower total water contents than finely crystalline zebraic chalcedony bands. The agates observed in this study display a narrow range of blue and orange to red color in CL response, and the overall CL intensity is low. The variations in textural properties, both macro- and microscopically, indicate an agate origin dominated by self-organizational processes without extensive external control.
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RECHARGE, DECOMPRESSION, AND COLLAPSE: DYNAMICS OF VOLCANIC PROCESSES
Benjamin James Andrews, Ph.D.
University of Texas at Austin, May 2009
Supervisor: James E. Gardner
264 pages, 100 references
Non-linear volcanic and magmatic processes control the occurrence and behavior of volcanic eruptions. Consequently, understanding the responses of volcanic systems to processes of different length scales, timescales, and magnitudes is critical to interpreting ancient deposits, understanding current eruption dynamics, and predicting future activity. Here I present the results of three studies wherein analytical geochemistry, experimental petrology, and turbulent flow analysis describe otherwise obscured volcanic processes.
Injections of new magma are common events in magma chambers. Recharging magma can change the chamber composition and temperature and may facilitate assimilation of country rock. Plagioclase phenocrysts provide an opportunity to examine recharge and assimilation processes, because their compositions are sensitive to temperature and their Sr isotopic ratios can record compositional variations in the chamber. Chemical and isotopic microanalyses of crystals from 7 eruptions of El Chichón Volcano, Mexico, reveal that recharge and assimilation events are very common and mixing is efficient, but individual events seldom affect the entire chamber.
During every eruption, magma decompresses and ascends through a conduit from a chamber at depth to a vent at the surface. Changes in pumice textures during the 1800 14C yr BP eruption of Ksudach Volcano, Kamchatka, suggest that conduit structure changed following caldera collapse. Decompression experiments show that the post-collapse pumice decompressed at ~0.0025 MPa/s, compared to pre-collapse decompression rates of >0.01 MPa/s. By balancing those results with eruptive mass fluxes I quantify the effects of caldera collapse on a conduit, and show that collapse resulted in a conduit with a very broad base and narrow vent.
Turbulent air entrainment controls whether an eruption column rises buoyantly or collapses to generate pyroclastic flows. Through extensive re-evaluation of video and photographs of the 18 May 1980 eruption of Mount St. Helens, I report the first measurements of the turbulent velocity field of a volcanic column and show that changes in its turbulence reflect changes in eruption behavior. Those results indicate collapse was caused by a reduction in eddy size and turbulent air entrainment initiated by an increased vent size and the development of a buoyant annulus surrounding a dense, collapsing core.
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HYDROGEOLOGICAL ANALYSIS OF GROUNDWATER CHEMISTRY AND SULFATE DISTRIBUTION, BLANCO AND HAYS COUNTIES, TEXAS
Megan J. Andring, M.S.Geo.Sci.
University of Texas at Austin, May 2010
Supervisor: John M. Sharp, Jr.
152 pages, 66 references, 7 tables
High concentrations of sulfate in groundwater, up to ten times the amount recommended by the EPA, in Blanco and Hays Counties, Texas, are of concern as groundwater pumping and population increase. The goals of this study are to characterize the chemistry of groundwaters in Blanco and Hays Counties within the context of Texas Groundwater Management Area-9 and to determine chemically and hydrogeologically the explanation for the spatial distribution of sulfate between the Pedernales River, the Blanco River, and Onion Creek. Insights gained by examining sulfate distribution in Blanco and Hays Counties can be applied to the other counties on the Edwards-Trinity Plateau with similarly high concentrations of sulfate in groundwater.
Hydrochemical data from the Cretaceous Edwards and Trinity Groups and water level measurements were used to analyze groundwater chemistry and flow. PHREEQC was used to examine whether phase changes in aquifer minerals could explain the observed geochemical patterns. COMSOL was used to develop a simplified groundwater flow model for a cross-sectional area between the Pedernales River and Onion Creek in Hays County.
Water levels indicate that groundwater generally flows southeast in the study area and most streams are gaining. The groundwater flow model indicates a zone of slow-moving groundwater beneath the topographic high between the Pedernales River, the Blanco River, and Onion Creek. Chemical analyses of well data show the presence of four groundwater chemical endmembers in Groundwater Management Area-9; a Ca-Mg-HCO3 fresh endmember, a Ca-Mg-SO4 endmember, a Ca-Mg-SO4-Na-Cl endmember, and a Na-Cl endmember. High sulfate waters generally come from the Upper and Middle Trinity aquifers while fresher waters are from the Edwards aquifer.
Physical and chemical analyses indicate that the zone of high sulfate in Blanco and Hays Counties may be the result of gypsum dissolution and dedolomitization in the Upper and Middle Trinity aquifers combined with low rates of groundwater flow beneath the topographic high. Groundwater flow analyses are consistent with those for the Groundwater Availability Models published for the region. Chemical analyses, specifically SO4 distributions and Ca/Mg ratios, are consistent with those found by Nance (2010) on the Edwards Plateau, farther west of the study area.
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RARE-EARTH-ELEMENT UPTAKE IN GARNET: TESTING COMPETING MODELS
Steven Joseph Arauza, B.S.
University of Texas at Austin, May 2009
Supervisor: William D. Carlson
51 pages, 11 references
Current models of REE uptake in garnet invoke either diffusion-limited (Skora et al. 2006) or reaction-controlled processes (Konrad-Schmolke et al. 2008) but are based on similar observations and samples. However, in some circumstances these models should result in different chemical zoning patterns. This study measured patterns of rare-earth-element (REE) concentrations in samples with bulk compositions and P-T conditions different from previous studies, in order to test the applicability of both models and to expand our understanding of this process. It documents previously undescribed patterns of REE zoning in garnet that testify to an unrecognized diversity and complexity in the process of REE uptake in garnet.
Seven garnets were analyzed from three localities representing different metamorphic facies and bulk compositions. Two large garnets from the Picuris Mountains, New Mexico, featured a pattern of HREE maxima and MREE minima in their cores. MREEs in these samples were localized in secondary peaks toward the rims. The smallest garnet from this locality featured maxima of all measured REE in the core of the crystal, with progressively wider peaks for lighter REEs. Two garnets from Passo del Sole, Switzerland featured similar patterns of single maxima in their cores for all REEs. Two garnets from the Franciscan Complex, California, showed irregular REE concentration patterns that were non-concentric.
Samples from the Picuris Mountains and Passo del Sole are interpreted as recording diffusion-controlled REE uptake in garnet. The consistent trend of wider peaks for MREEs in these samples implies slower rates of intergranular diffusion for MREEs than HREEs. In larger Picuris samples, spikes for all REEs in garnet interiors represent shifts in the garnet-forming reaction as had been identified in work by Crawford (2008). At these spikes, HREEs peak at the same point in the traverse while MREEs peak progressively further toward the rim due to slower rates of diffusion, recording the superposition of diffusional processes on a reaction event. Irregular patterns of REE concentration in Franciscan samples are representative of a completely different process of REE uptake from previous studies. The diversity of patterns uncovered in this study emphasizes the need for thorough characterization of REE patterns in garnet as a basis for proper geochronologic interpretation of Lu-Hf and Sm-Nd ages.
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CLIMATE VARIABILITY OVER THE AMERICAN MONSOON AND AMAZONIAN REGIONS DURING THE LAST DECADES
Paola Andrea Arias Gomez, PhD
University of Texas at Austin, August 2011
Supervisor: Rong Fu
144 pages, 148 references, 3 tables
This dissertation aims to identify the main changes in monsoon activity observed over the American monsoon and Amazonian regions during the last decades and the possible links between such changes. To address this, several observational and reanalysis datasets were used. The results suggest the occurrence of two regime types of the North American monsoon during 1948-2009: two dry regimes during 1948-1959 and 1990-2009 and one wet regime during 1960-1989. The occurrence of such regimes is modulated by the Atlantic Multidecadal Oscillation. However, the two dry regimes have different causes. In particular, the more recent dry regime is mainly due to both an anomalous westward expansion of the North Atlantic Subtropical High and a northward displacement of the subtropical jet stream over the United States. The former enhances the low-level flow from the Gulf of Mexico to the Great Plains and weakens moisture transport to Mexico and the southwestern US.
In addition to such a weakening of the North American monsoon during the last two decades, this research shows that the American monsoon systems have shortened after 1978 due to a trend toward earlier retreats of the North American monsoon and delayed onsets of the southern Amazon wet season. These changes produce a longer transition season between both monsoon systems. Whether these changes are caused by a common factor or they are the consequence of independent and unrelated causes was not clear previously. The results discussed here indicate that the observed changes in the American monsoons are partially a consequence of the westward expansion of the North Atlantic surface high observed since 1978. Such a westward expansion enhances the activity of easterly waves over the southern Caribbean Sea and northern South America, producing a dominant easterly flow over the region, which in turn prevents the reversal of the cross-equatorial flow necessary to transport moisture to the southern Amazon and the South American monsoon domain and contributes to its delayed onset.
This investigation provides evidence that the shortening and weakening of the American monsoons and the lengthening of the transition season between them are associated with the same large-scale forcing, which may be caused by anthropogenic influence.
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COPPER ISOTOPE ANALYSIS OF VEINS IN THE GRASBERG PORPHYRY CU-AU DEPOSIT PAPUA, INDONESIA: A PRELIMINARY STUDY
Sean Andrew Avitt, B.S.
University of Texas at Austin, May 2009
Supervisor: Mark Cloos
64 pages, 23 references
A 500 m long horizontal drill core (AM96-35-1) transects the three major intrusions and high grade Cu-Au mineralization in the Grasberg Igneous Complex (GIC). The mineralogy of veins was analyzed to select samples of chalcopyrite, bornite and covellite for Cu isotope analysis. About 53 % of veins sampled are Ccp+Qtz, Ccp+Anh, Ccp-only, Ccp+Qtz+Anh, or Ccp+Bnt+Anh mineral assemblages. Chalcopyrites from 19 veins from locations scattered along the length of the core have a range of δ65Cu ([(65Cu/63Cusample) / (65Cu/63Custandard) - 1] * 1,000) = -1.32 to 1.04 ‰ with an average of -0.15 ‰. The δ65Cu values obtained from analyses presented by Graham et al. (2004), and previous work by Dr. Todd B. Housh at the University of Texas at Austin are very similar to the data presented here.
The data set obtained to date at the UT-Austin consists of 37 samples and is considered a preliminary study. No correlation of δ65Cu is evident with coexisting minerals, intrusive unit, or distance from the center of the ore body. Graham et al. (2004) report a range of δ65Cu values for each of the three intrusive phases which they believe is evidence for three episodes of copper mineralization. However, the comparison of the data obtained in this study with Graham et al. (2004) is problematic because the analytical methodology used is different and they failed to consistently characterize their samples as grains within veins or disseminated in the host rock.
The δ65Cu values obtained in this study are within the range reported for copper minerals analyzed from chondritic meteorites and copper sulfides from black smoker deposits, suggesting a source that was mantle-derived. Further copper isotope evaluation of the AM96-35-1 core must be carried out to characterize disseminated copper mineralization, test for variability within veins, and to evaluate the effects of fractionation between coexisting copper sulfides. In addition, the Grasberg system must be evalutated at different levels to gain a fuller knowledge of copper isotope systematics within this hydrothermal ore deposit.
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PATTERNS AND PALEOSHORELINES OF WHITE SANDS DUNE FIELD, NEW MEXICO
Elke Elise Baitis, M.S. Geo. Sci.
University of Texas at Austin, May 2011
Supervisor: Gary Kocurek
52 pages, 16 references, 9 tables
The dune field at White Sands, New Mexico, shows a well-defined pattern of dunes and interdune areas, as well as spatial variations in this pattern. The purpose of this research is to determine which measured pattern parameters are most consistent across the dune field and to determine the cause of depositional spatial variability. This was accomplished using an airborne LiDAR generated digital-elevation model (DEM) collected in June 2007 and covering 39 km2 of the dune field. Properties of the dune field are defined by measurements from three dune populations: 1) 110 randomly selected dunes, 2) 247 dunes along transects oriented in the net transport direction, and 3) 171 dunes from three zones within the field where differences in pattern are visible. Measurements of eight common dune parameters show that the lowest coefficients of variation occur with dune orientation and crestline sinuosity, which largely define the field pattern. Cross-plotting of parameters shows generally poor correlations, which is thought to reflect variation around field-scale means that are comparable to other dune fields globally. Removing the dunes from the LiDAR DEM reveals a depositional substrate with breaks in slope interpreted as three paleoshorelines associated with Pleistocene Lake Otero. The paleoshorelines are antecedent boundary conditions that exert the primary control on spatial variability within the dune pattern.
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FORELAND BASIN EVOLUTION AND EXHUMATION ALONG THE DEFORMATION FRONT OF THE EASTERN CORDILLERA, NORTHERN ANDES, COLOMBIA
Alejandro Ezequiel Bande, MSGeo
University of Texas at Austin, August 2010
Supervisor: Brian K. Horton
106 pages, 90 references, 1 table
Tracking the phases of Cenozoic deformation in the Eastern Cordillera of Colombia has proven to be a challenging task. Clear disagreements remain in interpretations of the timing of uplift of the Eastern Cordillera, possibly based on difficulties in distinguishing first-cycle Central Cordillera grains from recycled Eastern Cordillera clasts. This thesis focuses on the Eocene–Pliocene sedimentary record of the eastern foothills of the Eastern Cordillera at a latitude of 6°N, integrating basin analysis with several provenance techniques in order to date the activation of several thrust systems.
Based on assessments of depositional environments and sediment dispersal patterns together with mineralogical and geochronological provenance, the onset of uplift in the axial zone of the Eastern Cordillera is constrained to be Oligocene. Prior to uplift, deposition in the eastern foothills was sourced from the eastern craton. Following the Oligocene episode, a continuous eastward advance of deformation is documented. An early Miocene episode probably reactivated the easternmost Cretaceous rift boundary along the eastern side of the Eastern Cordillera. Subsequent footwall shortcuts of those faults initiated activity in the middle to late Miocene, creating an intermontane (piggyback) basin in the eastern foothills at that time. In the preferred interpretation, this in-sequence history of thrust activation represents the main phases of deformation in the Eastern Cordillera from Eocene to Pliocene time, with neotectonic activity recording continued shortening.
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NATURAL FRACTURE CHARACTERIZATION, FRONTIER FORMATION, WYOMING
Brandon Louis Barber, MSGeoSci
University of Texas at Austin, May 2010
Supervisor: Stephen E. Laubach
251 pages, 175 references
Fractures can increase the permeability and producability of reservoirs by acting as fluid and gas conduits to wells. Networks of fractures are most important in reservoirs where little to no matrix permeability exists such as tight gas sandstones. Two significant variables, fracture length and the abundance of fractures, are not readily measurable from subsurface observations such as those obtained from cores or well logs. Numerical models suggest natural fracture apertures and lengths follow systematic power-law (Marrett, 1996; Olson, 2007) and negative exponential distributions (Olson, 2004); fracture trace lengths are interrogated. This study tests those propositions through study of fractures in outcrop.
Outcrops of the Cretaceous Frontier Formation at Oyster Ridge in southwest Wyoming and Oil Mountain near Casper, in central Wyoming provide evidence of reservoir scale fracture networks in sandstones. In the subsurface the Frontier Formation sandstones are reservoirs that produce gas and oil in several Wyoming basins. I mapped fracture patterns at twenty locations at Oyster Ridge and Oil Mountain and measured fracture trace length distributions and abundance (intensity). Fracture cumulative length distribution plots illustrate systematic length distributions.
Trace length distributions of every fracture network follow negative exponential distributions regardless of the number of fractures (N = 39 to N = 394) or the size of the outcrop (1.3 to 710 m2). Results show that the fractures follow a negative exponential distribution over a range of lengths of a few centimeters to tens of meters. These trace length distributions are consistent with geomechanical model fracture pattern simulation results by Olson (2004) that suggests negative exponential trace length distribution result from fracture to fracture interaction during fracture formation. Length distributions from my field study are inconsistent with pattern simulation results by Marrett (1996) and Olson (2007) and others that produce power-law length distributions. This inconsistency suggests that the model assumptions of Olson (2004) best account for the patterns I observed.
Two dimensional fracture intensity, defined as the total fracture trace length divided by the map area, was measured for each outcrop to determine how structural position affects fracture abundance patterns. Two-dimensional fracture intensity measurements collected at thirteen structural locations around Oil Mountain show higher values of fracture intensity near the fold-axial-trace compared to fold limbs. The difference is as much as 7.4 fractures per meter near fold hinges compared to 0.63 fractures per meter in fold limbs. Outcrops near small faults, with displacement of a few meters, show an increase in fracture intensity from background values around 4.8 fractures per meter to values nearly three times as high (13 fractures per meter) near faults. Values of fracture intensity that are more elevated near small tear faults imply that faulting has a greater influence on fracture intensity than folding.
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KINEMATICS OF BIDIRECTIONAL EXTENSION AND COEVAL NW-DIRECTED CONTRACTION IN ORTHOGNEISSES OF THE BIRANUP COMPLEX, ALBANY FRASER OROGEN, SOUTHWESTERN AUSTRALIA
Miriam Barquero-Molina, Ph.D.
University of Texas at Austin, May 2009
Supervisor: Sharon Mosher
205 pages, 124 references, 3 tables, 13 maps
Granulite-facies orthogneisses of the Mesoproterozoic Albany-Fraser Orogen from the locality of Bremer Bay, in southwestern Australia, record at least three phases of widespread, pervasive NW- and NE-trending bidirectional extension that alternate with shortening and/or shear related structures. Crustal extension occurred ca. 1180 Ma, based on SHRIMP U–Pb zircon geochronology of melts generated during deformation, which coincided with Stage II (1215-1140 Ma) of the Albany-Fraser Orogeny, a period of NW-directed contraction.
Eight different deformation phases can be recognized in the Bremer Bay area: (1) formation of a pervasive migmatitic fabric, defined by alternating leucosomes and melanosomes, parallel to the main compositional layering, and axial planar to localized isoclinal folds of cm-wide melt bands; (2) first bidirectional extension phase, which formed cm-scale square boudins of mafic layers parallel to the main migmatitic fabric; (3) formation of open to isoclinal, upright to overturned, SW-plunging, NW-verging m-scale folds of early square and rectangular boudins and dominant migmatitic foliation; (4) renewed coeval NE- and NW-directed extension that produced intermediate (< 1 meter to a few meters) boudins of the migmatitic fabric and compositional layering; (5) formation of regional-scale, NW-verging, SW-plunging overturned folds of all previous structures; (6) third phase of bidirectional extension that formed large, decameter-scale boudins of the migmatitic fabric; (7) late folding phase that resulted in the formation of m-scale open to tight, SW-plunging, upright to moderately overturned, NW-verging folds; and (8) fracturing related to the intrusion of dominantly N-NW- and N-NE-trending intermediate and felsic few cm- to few dm-wide pegmatite veins. Melt generation was concurrent with all stages of deformation.
The Albany-Fraser Orogen is reinterpreted as a diachronous orogen, resulting from the closure of the asymmetrically shaped ocean basin between the West Australian and Mawson cratons, which widens considerably from NE to SW along the length of the orogenic front. Subduction on the western side of the orogen was the driving force for NW-directed collision during Stage II of the orogeny.
Slab breakoff and orogenic collapse following closure of an intracratonic ocean basin could account for the multiple phases of bidirectional extension, granulite facies metamorphism and pervasive partial melting throughout deformation.
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SEASONAL SOIL MOISTURE DYNAMICS THROUGHOUT A SEMIARID VALLEY ECOTONE USING QUASI-3D TIME-LAPSE ELECTRICAL RESISTIVITY IMAGING
Benjamin Jacob Bass, BS
University of Texas at Austin, December 2011
Supervisor: M. Bayard Cardenas
92 pages, 110 references, 5 tables
This study investigates the spatial distribution and seasonal variation of soil moisture conditions throughout a first-order drainage basin characterized by opposing hillslopes with distinct vegetation types and soil properties. The study site, located 75 km south of Albuquerque, NM in the Sevilleta National Wildlife Refuge, hosts a pronounced ecotone (ecosystem boundary), but is representative of the hillslopes in the region. The north-facing slope of the valley is characterized by deep rooted juniper trees and finer soils, while desert-adapted creosote bushes are the dominant vegetation on the south-facing slope as a result of the roughly 20% greater annual solar radiation received on this slope in comparison to the north-facing slope. A series of multiple time-lapse, quasi-3D electrical resistivity (ER) measurements were made using 56 electrodes with a 1.5 m electrode spacing for four seasons from November 26th, 2010 to August 11th, 2011 to capture seasonal soil moisture changes down to a depth of 21 m throughout the 300 x 125 m study valley site. An extensive prolonged drought associated with La Nina Southern Oscillation resulted in time-lapse ER profiles that demonstrate the spatial and temporal water uptake strategies of the desert-perennials found at the study site. Results indicate that both juniper and creosote bushes utilize their maximum rooting depths to uptake water stored at deeper horizons during prolonged drought conditions when shallower soil moisture is not available. Furthermore, results suggest that no water is capable of draining past the root zone of either type of vegetation to result in recharge, explained hydrologically by evapotranspiration rates on both hillslopes that are greater than the mean annual precipitation. The different vegetation types in the study area affect surface-atmosphere fluxes as well as the potential for recharge even during the La Nina drought when soil moisture conditions in the vadose zone are expected to be static; findings from this project have important implications for climatic and hydrological conditions in semiarid basins found in the southwestern U.S.A.
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LASER-MAPPING AND 3D RECONSTRUCTION OF THE LOWER ORDOVICIAN EL PASO GROUP BRECCIA COLLAPSE BRECCIAS, FRANKLIN MOUNTAINS, TEXAS
Jerome Anthony Bellian, Ph.D.
University of Texas at Austin, August 2009
Supervisor: Charles Kerans
211 pages, 158 references, 7 tables, 4 plates
The Lower Ordovician El Paso Group is a >400-m-thick carbonate succession exposed in the Franklin Mountains, El Paso, Texas. The El Paso Group contains multiple breccias related to collapsed-paleocave systems. These breccias have been documented as having formed during the top-Lower Ordovician Sauk depositional supersequence lowstand. Evidence presented in this study suggests that cave formation may have been as much as 350 millions years younger and related to Laramide oblique right lateral compression. Regardless of the timing of formation, the breccias mapped in this study are of collapsed paleocave origin based on breccia clast organization and matrix content.
Speleogenetic models are compared against observations of breccia distribution by direct field observations and mapping on sub-meter airborne light detection and ranging or lidar data. Point vectors were defined for every point within study area to highlight subtle changes in outcrop erosional profile for mapping geological features directly on the lidar point cloud. In addition, spectral data from airborne photography and hyperspectral image analysis were used assist in geological contact definition.
A digital outcrop model was constructed from 3D geologic mapping results from which spatial statistic were extracted and used to reconstruct collapsed paleocave breccia bodies. The resultant breccia geometries were compared against laser-scanned modern cave dimensions, from Devil's Sinkhole, Rocksprings, Texas, and used in analysis of conceptual models for cave formation.
The breccias of the southern Franklin Mountains follow linear trends that closely match Riedel shear fracture patterns predicted from right-lateral oblique compression. Stress orientations that match right-lateral oblique compression in the Phanerozoic of the El Paso region are related to the Laramide orogeny. The relationship of observed structures and the orientation of collapse breccias may indicate that southern Franklin Mountain breccia bodies are the result of a solution-enhanced tectonic karst system.
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ARCHITECTURE OF DEPOSITS FORMED IN A TECTONICALLY GENERATED TIDAL STRAIT, UPPER BARONIA FM., AGER BASIN, SOUTH CENTRAL PYRENEES, SPAIN
Ashley Elizabeth Bens, MSGeoSci
University of Texas at Austin, May 2011
Supervisor: Ronald J. Steel
86 pages, 75 references, 1 table
The upper Baronia Fm. of the Ager Basin, Spain, is composed of a hierarchy of prominently stacked sets of primarily unidirectional cross-strata in units up to 40m thick. These large sets of cross-strata are interpreted as deposits of migrating subaqueous tidal simple dunes, compound dunes, and compound dune complexes within an approximately 10km wide north-east to south-west oriented seaway with water depths of a calculated 60-90m. These interpretations are opposed to prior interpretations of the upper Baronia Fm. which suggests deposits were formed by tidal bars within a deltaic environment (Mutti et al., 1985). Dunes developed due to dominantly north-east directed tidal currents driven through the strait by tidal phase differences between the two bodies of water (Mediterranean and Atlantic basins) connected by the seaway. Evidence for syn-tectonic deposition further constrains timing of movement of the northern basin bounding Montsec thrust to the early Eocene. Indicators for movement on the Montsec thrust include the development of the Ager Basin elongate to the thrust front, and syn-tectonic signals in the fill of the basin such as local conglomerate wedges and emplacement of olistoliths.
Individual cross-stratified successions are interpreted to have formed with variable flow velocity and orientation, resulting in a basin wide stacking of compound dune complexes. These compound dune complexes form cross stratified successions which are distributed throughout the basin according to the variable current speeds, dune size which impacts migration, and sediment availability during deposition. This results in the observed distributions of muddy and sandy sediments, where finer grained materials accumulate preferentially in the low energy troughs of the hierarchy of compound dunes.
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PALEOCAVES AND ASSOCIATED FEATURES IN THE LOWER CRETACEOUS SEGOVIA FORMATION, WESTERN EDWARDS PLATEAU, WEST TEXAS
Randy Howard Caber Jr., M.S.Geo.Sci.
University of Texas at Austin, May 2010
Co-Supervisors: Robert G. Loucks and Xavier Janson
164 pages, 100 references, 9 tables
Paleocaves in carbonates within Middle Cretaceous Segovia Formation of the western Edwards Plateau suggest a history of development beginning as ellipsoid phreatic passages that evolved into vadose passages as regional groundwater base level dropped. Composite caves range in size from over 20 meters high to less than a 1 meter high and 15 meters wide to less than 1 meter wide. Paleocave morphology and sediment patterns provide insight into the long-term morphological evolution of the Western Edwards Plateau in West Texas.
Stratigraphic locations of the paleocaves across the western Edwards Plateau were compared to a 10 to 30 cm regional clay-marker bed that can be mapped for over a distance of 100 km. The regional clay-marker bed is associated with a high-frequency-sequence boundary (Zahm, 1997) interpreted to have formed during a sea-level lowstand, which produced a platform exposure event. The location of paleocaves in the western Edwards Plateau are controlled by numerous factors, but the dominating factors are the stratigraphic position of the paleocaves in relation to the bedding planes and fractures in the host rock.
The cave sediments display a range of sedimentologic structures from erosional channels and mud cracks, and highly ordered laminated textures to chaotic conglomerates. The preponderance of carbonate mud, silt, sand, and other grain sizes reflect the erosion of a carbonate terrain; sedimentary structures found include ripple laminations, upward fining sequences, erosional events, chaotic deposits, and desiccation of sediment. The mineralogy of the sediments found within the paleocaves includes calcite, quartz, minor amounts of lithics, and various clays. Detrital grains eroded from superjacent strata and identified by allochems and textures are also incorporated in the cave sediment.
Speleothems, including stalagmites, stalactites, and flowstones are found on the paleocave walls and interbedded within the sediment fill. Flowstones excavated from the paleocaves display sharp bands of alternating light and dark calcite. Speleothem growth is evidence for the caves being open and for the presence of meteoric waters flowing though the voids. Uranium-series analysis of speleothem material provides minimum paleocave-age estimates, which indicate the paleokarst to be older than 500 ka. The occurrence of Upper Cretaceous rock fragments within the sediment fill of the caves that occur in Lower Cretaceous strata, offers a possible upper age of Late Eocene speleogenesis. This is based upon when the Upper Cretaceous strata were available for erosion.
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TECTONOSTRATIGRAPHIC AND SUBSIDENCE HISTORY OF THE NORTHERN LLANOS FORELAND BASIN OF COLOMBIA
Henry Miguel Campos, M.S. Geo. Sci.
University of Texas at Austin, August 2011
Supervisor: Paul Mann
109 pages, 145 references, 2 tables
The Llanos foreland basin of Colombia is located along the eastern margin of the northern Andes. The Llanos basin is bounded to the north by the Mérida Andes, to the east by the Guiana shield, to the south by the Serrania de la Macarena, and to the west by the frontal foothills thrust system of the Andes (the Cordillera Oriental). The Llanos foreland basin originated in the Maastrichtian, after a post-rift period during the Mesozoic, and recorded an abrupt pulse of middle Miocene subsidence possibly in response to subduction and collision events along the Pacific margin of northwestern South America. Regional east-west shortening, driven in part by collision of the Panama arc along the Pacific margin of Colombia, has built the widest part of the northern Andes. This wide area (~600 km) includes a prominent arcuate thrust salient, the Cordillera Oriental, which overthrusts the Llanos foreland along a broad V-shaped salient that projects 40 km over the northern Llanos foreland basin. In this study, I interpret 1200 km of 2D seismic data tied to 18 wells and regional potential fields (gravity and magnetic) data. Interpreted seismic data are organized into four regional (300 to 400-km-long) transects spanning the thrust salient area of the northern Llanos basin.
I performed 2D flexural modeling on the four transects in order to understand the relative contributions of flexural subsidence due to tectonic and sedimentary loading. Sedimentary backstripping was applied to the observed structure maps of six Eocene to Pleistocene interpreted horizons in the foreland basin in order to remove the effects of sedimentary and water loading. Regional subsidence curves show an increase in the rate of tectonic subsidence in the thrust salient sector of the foreland basin during the middle to late Miocene. The flexural models predict changes in the middle Miocene to recent position of the eastern limit of foreland basin sediments as well as the changing location and vertical relief of the flexurally controlled forebulge. Production areas of light oil in the thrust belt and foreland basin are located either south of the thrust salient (Cusiana, Castilla, Rubiales oilfields) or north of the salient (Guafita-Caño Limon, Arauca oilfields) but not directly adjacent to the salient apex where subsidence, source rock thicknesses, and fracturing were predicted by a previous study to be most favorable for hydrocarbons. There are no reported light oil accumulations focused on the predicted present or past positions of the forebulge, but detailed comparisons of seismic reflection data with model predictions may reveal stratigraphic onlap and/or wedging relationships that could provide possible traps for hydrocarbons.
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ABSTRACT MONETIZING STRANDED GAS: ECONOMIC VALUATION OF GTL AND LNG PROJECTS
Brodie Gene Black, M.A.
University of Texas at Austin, May 2010
Supervisor: Christopher J. Jablonowski
77 pages, 39 references
Globally, there are significant quantities of natural gas reserves that lie economically or physically stranded from markets. Options to monetize such reserves include Gas to Liquids (GTL) and Liquefied Natural Gas (LNG) technologies. GTL is a unique monetization option that brings natural gas products to crude oil markets. This technology is commercially immature, appears to have attractive market potential, requires substantial capital investments, and has uncertain operating costs and revenue generation. LNG is a more established monetization option. Project economics for the two technologies are reviewed, as well as literature evaluating such for either or both. Discounted cash flow models are studied for two project scenarios, and results are discussed and compared. The modeling effort seeks to inform the decision to invest in GTL or LNG for the monetization of a stranded gas reserve.
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THE INFLUENCE OF SEA SURFACE TEMPERATURE AND VARIABILITY OF THE NORTH ATLANTIC SUBTROPICAL HIGH ON MULTIDECADAL DROUGHT IN TEXAS.
Adam R. Bowerman, B.S. General Geology
University of Texas at Austin, December 2011
Supervisor: Rong Fu
68 pages, 18 references, 3 tables
Intense drought is of great concern to the state of Texas, as well as the rest of the American Southwest. Although droughts in Texas is linked to La Niña events, the relationship between the strength of the drought and that of La Niña is complex. This study explores how other factors, in particular sea surface temperature and pressure variability in the Atlantic and Pacific, influence the hydrology of the ten individual climate divisions of Texas. In an effort to understand the mechanism of Pacific subtropical sea surface temperature forcing on atmospheric circulation in the Atlantic Basin, a detailed look at the relationship between the Pacific Decadal Oscillation and the North Atlantic Subtropical High provides insights into the role of the subtropical high in drought occurrence and severity. It is found that during positive (negative) events of the Pacific Decadal Oscillation, the North Atlantic Subtropical High migrates equatorward (poleward) and westward (eastward) by 1.5° - 3.0° latitude, with similar motion seen in the 200 hPa Northern Hemisphere subtropical jet.
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MULTIAZIMUTH VELOCITY ANALYSIS USING VELOCITY-INDEPENDENT SEISMIC IMAGING
William Andrew Burnett, Ph.D.
University of Texas at Austin, May 2011
Supervisors: Sergey Fomel and Paul Stoffa
136 pages, 111 references, 1 table
Multiazimuth seismic data contains information about how the Earth's seismic response changes with azimuthal direction. Directional-dependence of the seismic response can be caused by anisotropy or heterogeneity, associated with subsurface features such as fractures, stresses, or structure. Characterizing azimuthal variations is done through velocity analysis, which provides a link between an acquired data set and its image, as well as between the image and subsurface geology. At the stage which conventional velocity analysis is applied, it is difficult to distinguish the geologic cause of observed azimuthal velocity variations. The inability to distinguish the similar effects of anisotropy and heterogeneity leads to positioning errors in the final image and velocity estimates. Regardless of the cause, azimuthally variable velocities require at least three parameters to characterize, as opposed to the conventional single-parameter isotropic velocity. The semblance scan is the conventional tool for seismic velocity analysis, but it was designed for the isotropic case. For multiple parameters, the semblance scan becomes computationally impractical. In order to help address the issues of geologic ambiguity and computational efficiency, I develop three methods for multiazimuth seismic velocity analysis based on "velocity-independent" imaging techniques. I call this approach, velocity analysis by velocity-independent imaging, where I reverse the conventional order of velocity estimation followed by image estimation. All three methods measure time-domain effective-velocity parameters. The first method, 3D azimuthally anisotropic velocity-independent NMO, replaces the explicit measurement of velocity with local slope detection. The second method, time-warping, uses local slope information to predict traveltime surfaces without any moveout assumption beforehand, and then fit them with a multiparameter velocity model. The third method, azimuthal velocity continuation, uses diffraction image focusing as a velocity analysis criterion, thereby performing imaging and velocity analysis simultaneously. The first two methods are superior to the semblance scan in terms of computational efficiency and their ability to handle multi-parameter models. The third method is similar to a single multi-parameter semblance scan in computational cost, but it helps handle the ambiguity between structural heterogeneity and anisotropy, which leads to better positioned images and velocity estimates.
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GEOLOGICALLY-BASED PERMEABILITY ANISOTROPY ESTIMATES FOR TIDALLY-INFLUENCED RESERVOIR ANALOGS USING LIDAR-DERIVED QUANTITATIVE SHALE CHARACTER DATA
Darrin Burton, PhD
University of Texas at Austin, May 2011
Supervisor: Lesli Wood
220 pages, 210 references, 3 tables
The principle source of heterogeneity affecting flow behavior in conventional clastic reservoirs is discontinuous, low-permeability mudstone beds and laminae (shales). Simple 'streamline' models have been developed which relate permeability anisotropy (kv/kh) at the reservoir scale to shale geometry, fraction, and vertical frequency. A limitation of these models, especially for tidally-influenced reservoirs, is the lack of quantitative geologic inputs. While qualitative models exist that predict shale character in tidally-influenced environments (with the largest shales being deposited near the turbidity maximum in estuaries, and in the prodelta-delta front), little quantitative shale character data is available. The purpose of this dissertation is to collect quantitative data to test hypothetical relationships between depositional environment and shale character and to use this data to make geologically-based estimates of kv/kh for different reservoir elements.
For this study, high-resolution, lidar point-clouds were used to measure shale length, thickness, and frequency. This dissertation reports a novel method for using distance-corrected lidar intensity returns to distinguish sandstone and mudstone lithology. Lidar spectral and spatial data, photo panels, and outcrop measurements were used to map and quantify shale character.
Detailed shale characteristics were measured from four different tidally-influenced reservoir analogs: estuarine point bar (McMurray Formation, Alberta, Canada), tidal sand ridge (Tocito Sandstone, New Mexico), and unconfined and confined tidal bars (Sego Sandstone, Utah). Estuarine point bars have long (l =67.8 m) shales that are thick and frequent relative to the other units. Tidal sand ridges have short (l =8.6 m dip orientation) shales that are thin and frequent. Confined tidal bars contain shales that are thin, infrequent, and anisotropic, averaging 16.3 m in length (dip orientation). Unconfined tidal bars contain nearly equidimensional (l =18.6 m dip orientation) shales with moderate thicknesses and vertical frequency. The observed shale geometries agree well with conceptual models for tidal environments.
The unique shale character of each unit results in a different distribution of estimated kv/kh. The average estimated kv/kh values for each reservoir element are: 8.2x10-4 for estuarine point bars, 0.038 for confined tidal bars, 0.004 for unconfined tidal bars, and .011 for tidal sand ridges.
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DEPOSITIONAL HISTORY OF THE TARANAKI BASIN, NEW ZEALAND: LINKING SEDIMENT ACCUMULATION AND SUBSIDENCE RATES TO TECTONIC PROCESSES
Paola Cardona, MSGeoSci
University of Texas at Austin, May 2009
Supervisor: William L. Fisher
Co-supervisor: Brian Horton
106 pages, 78 references, 8 tables
Geohistory (subsidence) analysis was performed in the Northern Graben of the offshore Taranaki Basin, located along the western coast of New Zealand’s North Island. The Taranaki Basin has a complex tectonic history, which is reflected in changes in Late Cretaceous-Cenozoic depositional patterns. Understanding the subsidence history and how it affected basin development is crucial to defining the structural and stratigraphic changes that took place during its evolution.
A reconstruction of the depositional history of the basin through seismic interpretation of about 630 km2 of the Parihaka 3D seismic volume and mapping of several horizons within the stratigraphic succession allowed identification of depocenters and spatial changes in thickness. This analysis is complemented by subsequent measurement of sediment accumulation based on amount of sediment preserved, and a general description of the main structural and stratigraphic features observed during 3D seismic volume interpretation. Backstripping techniques were used to determine the tectonic subsidence after isolating the subsidence due to water and sediment load.
The Taranaki Basin was formed by extension associated with Tasman Sea spreading during the Late Cretaceous to early Oligocene. The basin was initially a rift basin, in which Late Cretaceous to Paleozoic deposition was confined to half grabens and sediments were predominantly fluvial and shallow marine. During a subsequent period of drift and quiescence, that started at late Paleocene a carbonate platform developed for most of the Oligocene. This was followed by a Miocene compressional regime creating a deep basin filled with a thick and complex succession of deep marine sediments in a back-arc foreland basin related to the convergent plate boundary between the Australian and Pacific plates. Different types of subsidence (fault-controlled subsidence, thermal, and subsidence related to sediment load) are recognizable, as are periods of non-deposition.
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VOLUMETRIC ANALYSIS OF THE BONY LABYRINTH OF BATS: APPARENT REDUCTION IN THE EVOLUTION OF THE VESTIBULAR APPARATUS
Joey Carlin, BS
University of Texas at Austin, May 2009
Supervisor: Christopher J. Bell
I used high-resolution x-ray computed tomography to investigate the hollow space within the petrosal bone of 23 different species of bat. I segmented the inner ear cavity into recognizable structures that correspond to soft tissues of the cochlea and semicircular canals (vestibular apparatus). I calculated the volume of each structure and its percent contribution to the total volume of the petrosal cavity. A comparable data set was used to generate a baseline condition for terrestrial (non-volant) mammals.
The vestibular apparatus in bats occupies a significantly lower percentage of the petrosal cavity compared to terrestrial mammals (the mean percentage for bats is 29.9% compared to a mean percentage of 43.7% for terrestrial mammals). This finding is analogous to the reduction of the vestibular apparatus observed in cetaceans and supports the hypothesis that moving in a three-dimensional fluid media introduces selective pressure favoring smaller vestibular structures.
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THE MODERN ASSESSMENT OF CLIMATE, CALCITE GROWTH, AND THE GEOCHEMISTRY OF CAVE DRIP WATERS AS A PRECURSOR TO PALEOCLIMATE STUDY
Richard Cain Casteel, M.S. Geo. Sci.
University of Texas at Austin, August 2011
Supervisor: Jay L. Banner
165 pages, 92 references, 6 tables
The overall goal of this study is to determine the resolution and type of proxy that any one drip site can provide for the determination of past climate. The study examines surface conditions (effective rainfall, temperature, PDSI), cave characteristics (cave geometry, cave air CO2, location), drip site characteristics (drip rate, drip rate response to rainfall), and drip water characteristics (pH, trace element ratios, alkalinity, temperature). The study encompasses two distinctly different caves, Inner Space Cavern (Chapter 2) and Westcave (Chapter 3).
A goal of Chapter 2 is to identify drip sites where there is an intra-annual climate signal, which can assist with high resolution paleo-drought reconstructions when extended to speleothem studies. To be considered an intra-annual climate sensitive drip site, a site should display statistically significant correlations between (1) effective rainfall and drip rate; (2) effective rainfall and Mg/Ca; (3) drip rate and Mg/Ca; (4) Palmer Drought Severity Index (PDSI) and drip rate; and (5) PDSI and Mg/Ca. These relationships can be explained by the extent to which water flux in the karst overburden influences flow path characteristics, water residence time, and water-rock interactions.
The data in Chapter 3 will indicate that (1) variations in trace element/Ca values in cave drip waters are temperature dependent and vary on a seasonal time scale, (2) the standardization of trace element/Ca values allows for between drip site comparisons, (3) the standardization of trace element/Ca values can add statistical power to statistical analyses by increasing the sample size, (4) calcite growth rates follow a seasonal pattern based on variations in surface temperature, (5) a regional drought indicator provides correlation with trace element/Ca values at some drip sites and this relationship is most likely dependent upon temperature.
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INTEGRATED ANALYSIS TO OPTIMIZE HYDRAULIC FRACTURING TREATMENT DESIGN IN A CLASTIC AND CARBONATE FORMATION IN TORUNOS HYDROCARBON FIELD, BARINAS - APURE BASIN, SOUTHWEST VENEZUELA
Libsen Marelis Castillo, M.A.
University of Texas at Austin, May 2009
Supervisor: Jon E. Olson
120 pages, 70 references, 16 tables
Hydraulic fracturing treatments are a common practice in a variety of hydrocarbon fields around the world. Three of these treatments have been performed in the Torunos field of southwest Venezuela. One was executed in the Gobernador “A/B” formation in which the fracture reached a water zone located nearby. The other two treatments were performed in the Escandalosa “O” formation. Placing the proppant into the formation was problematic owing to propagation of multiple hydraulic fractures and excessive leak-off. Today, several wells are inactive because of low productivity. Such wells could be potential candidates for reactivation by hydraulic fracturing if the problems encountered in previous treatments can be avoided. Therefore, the purpose of this study is to optimize the design of hydraulic fracturing treatments in the formations under consideration while avoiding the problems encountered in the previous attempts.
Experimental design and response surface methods were used to perform sensitivity analyses and to evaluate uncertainty to optimize the design of hydraulic fracturing treatments. Experimental design was used to generate a reduced number of cases with simultaneous combinations of uncertain variables. Simulation of the cases generated was then performed, assisted by a commercial simulator. Response surface method was used to develop surrogate equation models that fit the simulation responses. Monte Carlos analysis was performed to estimate the probability distribution function of the propped fracture length, propped fracture height, depth to the fracture bottom, and net present value (NPV) to select the optimum designs based on technical, economical, and risk analyses.
The results show that the optimum hydraulic fracturing treatment design for the Gobernador “A/B” formation should involve small slurry volume (around 300 bbl), a low injection rate (between 6 bbl/min and 8 bbl/min), and low viscosity crosslinked fluid (50 cp). This will control the fracture height and avoid fracturing the water zone. Moreover, reducing the perforated interval to around 20 ft and using low density shot (1 SPF) will help to minimize the propagation of multiple hydraulic fractures in the Escandalosa “O” formation. Finally, the optimum injection rate and slurry volume in this formation are 20 bbl/min and 800 bbl respectively.
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FORMATION OF MINERALOGICAL ZONATIONS IN OPHIOLITES THROUGH REACTIVE POROUS FLOW: A MODELING STUDY
Jennifer Lynn Cessna, MS GeoSci
University of Texas at Austin, May 2011
Supervisor: Marc Hesse
75 pages, 30 references, 3 tables
In the mantle section of many ophiolite sequences, dunite dikes are present. Around dunite dikes at the Josephine and Trinity ophiolite, a sequence of lithologies consisting of plagioclase lherzolite, lherzolite, and harzburgite is present. This sequence of rocks has been interpreted to be the result of reactive porous flow. From trace element data, the mafic melt has been interpreted to flow both into and out of the dunite dikes. Whether the melt emanates from the dunite bodies or is collected by them has implications for the mechanisms of melt extraction beneath ridge systems. The determination of the flow direction based on tracer distributions is difficult and therefore additional constraints are important. Reactive transport theory predicts that lithological zonations around dunite bodies can indicate the direction of flow.
To date no reactive transport model has been developed to test these hypotheses, and therefore I have built a reactive transport model using COMSOL v. 4.1. I developed a model for an orthopyroxene dissolution front based on the model of Chadam et al. (1986, Reactive infiltration instabilities, IMA Journal of Applied Mathematics, v. 36, p.207-221). This model includes the strong nonlinearity feedback that has been invoked to lead to the channelization of melt flow. The instability leads to the formation of elongated regions where orthopyroxene is depleted. This model predicts that the melt is focused into the dunite bodies, most flow is parallel to the dunite boundaries, and exits the fingers at the tip of the column.
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INTEGRATION OF FACIES MODELS IN RESERVOIR SIMULATION
Lin Chang, M.A.
University of Texas at Austin, December 2010
Supervisor: William L. Fisher
97 pages, 71 references, 8 tables
The primary controls on subsurface reservoir heterogeneities and fluid flow characteristics are sedimentary facies architecture and petrophysical rock fabric distribution in clastic reservoirs and in carbonate reservoirs, respectively. Facies models are critical and fundamental for summarizing facies and facies architecture in data-rich areas. Facies models also assist in predicting the spatial architectural trend of sedimentary facies in other areas where subsurface information is lacking.
The method for transferring geological information from different facies models into digital data and then generating associated numerical models is called facies modeling or geological modeling. Facies modeling is also vital to reservoir simulation and reservoir characterization analysis. By extensively studying and reviewing the relevant research in the published literature, this report identifies and analyzes the best and most detailed geologic data that can be used in facies modeling, and the most current geostatistical and stochastic methods applicable to facies modeling.
Through intensive study of recent literature, the author (1) summarizes the basic concepts and their applications to facies and facies models, and discusses a variety of numerical modeling methods, including geostatistics and stochastic facies modeling, such as variogram-based geostatistics modeling, object-based stochastic modeling, and multiple-point geostatistics modeling; and (2) recognizes that the most effective way to characterize reservoir is to integrate data from multiple sources, such as well data, outcrop data, modern analogs, and seismic interpretation. Detailed and more accurate parameters using in facies modeling, including grain size, grain type, grain sorting, sedimentary structures, and diagenesis, are gained through this multidisciplinary analysis. The report concludes that facies and facies models are scale dependent, and that attention should be paid to scale-related issues in order to choose appropriate methods and parameters to meet facies modeling requirements.
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UNCONVENTIONAL RESOURCES: ECONOMIC ANALYSIS AND TECHNOLOGY TO PRODUCE SYNTHETIC CRUDE OIL
Jose E. Chavez, M.A.
University of Texas at Austin, May 2009
Supervisor: Charles G. Groat
202 pages, 136 references, 17 tables
As global demand for energy increases and conventional oil and natural gas production seems insufficient at keeping up with the pace of today’s demand growth projections, more attention is being paid to unconventional and alternative sources of energy. Renewable energy should be considered as a major contributing factor to the solution. However, it will take decades to obtain a significant share in the energy mix of both developed and developing countries, while the world continues to use hydrocarbons, particularly for transportation.
An important component of this new energy supply will come from unconventional sources, especially those consistent with the existing infrastructure for producing, refining, distributing and consuming petroleum-based fuels.
This thesis scrutinizes the potential contributions of unconventional sources to future world energy supplies, in particular North and Latin America. It also analyzes the current production of unconventional oil and reviews some of the costs, technologies and environmental challenges currently associated with the extraction of this resource and its conversion into synthetic crude oil.
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SEISMIC MODELING AND IMAGING WITH THE FOURIER METHOD: NUMERICAL ANALYSES AND PARALLEL IMPLEMENTATION STRATEGIES
Chunlei Chu, Ph.D.
University of Texas at Austin, December 2009
Supervisor: Paul L. Stoffa
367 pages, 249 references, 2 tables
Our knowledge of elastic wave propagation in general heterogeneous media with complex geological structures comes principally from numerical simulations. In this dissertation, I demonstrate through rigorous theoretical analyses and comprehensive numerical experiments that the Fourier method is a suitable method of choice for large scale 3D seismic modeling and imaging problems, due to its high accuracy and computational efficiency. The most attractive feature of the Fourier method is its ability to produce highly accurate solutions on relatively coarser grids, compared with other numerical methods for solving wave equations. To further advance the Fourier method, I identify two aspects of the method to focus on in this work, i.e., its implementation on modern clusters of computers and efficient high-order time stepping schemes.
I propose two new parallel algorithms to improve the efficiency of the Fourier method on distributed memory systems using MPI. The first algorithm employs non-blocking all-to-all communications to optimize the conventional parallel Fourier modeling workflows by overlapping communication with computation. With a carefully designed communication-computation overlapping mechanism, a large amount of communication overhead can be concealed when implementing different kinds of wave equations. The second algorithm combines the advantages of both the Fourier method and the finite difference method by using convolutional high-order finite difference operators to evaluate the spatial derivatives in the decomposed direction. The high-order convolutional finite difference method guarantees a satisfactory accuracy and provides the flexibility of using non-blocking point-to-point communications for efficient inter-processor data exchange and the possibility of overlapping communication and computation. As a result, this hybrid method achieves an optimized balance between numerical accuracy and computational efficiency.
To improve the overall accuracy of time domain Fourier simulations, I propose a family of new high-order time stepping schemes, based on a novel algorithm for designing time integration operators, to reduce temporal derivative discretization errors in a cost-effective fashion. I explore the pseudo-analytical method and propose high-order formulations to further improve its accuracy and ability to deal with spatial heterogeneities. I also extend the pseudo-analytical method to solve the variable-density acoustic and elastic wave equations.
I thoroughly examine the finite difference method by conducting complete numerical dispersion and stability analyses. I comprehensively compare the finite difference method with the Fourier method and provide a series of detailed benchmarking tests of these two methods under a number of different simulation configurations. The Fourier method outperforms the finite difference method, in terms of both accuracy and efficiency, for both the theoretical studies and the numerical experiments, which provides solid evidence that the Fourier method is a superior scheme for large scale seismic modeling and imaging problems.
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TRENDS IN EVOLUTIONARY MORPHOLOGY: A CASE STUDY IN THE RELATIONSHIPS OF ANGEL SHARKS AND BATOID FISHES
Kerin Michele Claeson, PhD
University of Texas at Austin, May 2010
Supervisor: Christopher J. Bell
254 pages, 142 references, 4 tables
Chondrichthyans are cartilaginous fishes that include the extant chimaeras, sharks, and batoids, and their extinct relatives. In this dissertation, I examined the growth, development, and relationships of extinct and extant chondrichthyans. I reexamined the skeleton of fossil and fetal specimens of the angel sharks (Squatiniformes) and reanalyzed the current morphologically based hypothesis of chondrichthyan evolution, which conflicts with the current molecular based hypothesis. I did this by including extinct taxa and new characters based on dentition, and the ethmoid, occipital, pectoral, and vertebral skeleton. My results supported the pre-existing morphological hypothesis that angel sharks, saw sharks, and batoids form a clade. However, some of my new characters, particularly those based on the vertebral morphology, indicate that fetal and juvenile angel sharks do not share as many apomorphies with batoids as previously hypothesized from the examination of adults.
I also examine the relationships of major groups within batoids, beginning with the construction of a hypothesis of the evolutionary history of electric rays (Torpediniformes). My results are consistent with previous rank-based classi?cations. However, they deviate from previous classifications depending on the criteria used to generate the hypothesis and on which taxon, or combination of taxa, were used to root the ingroup phylogeny.
Because pectoral and vertebral morphology are so critical to morphological hypotheses, I also examined the growth and development of the synarcual cartilage in batoid fishes, with particular emphasis on the synarcual of skates (Rajiformes). My results demonstrate that calcification and chondrification do not proceed in the same order, temporally and spatially. Finally, I redescribe the extinct batoid †Cyclobatis, known only from the Cretaceous, and evaluate its phylogenetic position. My results indicate that †Cyclobatis, the oldest known rajid, is also the sister taxon to a clade of all known extant members of Rajidae. Furthermore, the inclusion of new characters, mainly derived from the synarcual, help to resolve the interrelationships of Rajidae.
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STRATIGRAPHY AND RESERVOIR ARCHITECTURE OF A PERMIAN TOE-OF-SLOPE OOID FAN, HAPPY (SPRABERRY) FIELD, GARZA CO., TEXAS
Jason L. Clayton, M.S.Geo.Sci.
University of Texas at Austin, May 2011
Supervisor: Charles Kerans
90 pages, 57 references, 3 tables
The Permian (Leonardian) aged Upper Spraberry Formation found in the Happy Field of Garza Co. TX, contains one of the best examples of a reservoir composed of resedimented carbonates in a deep-water slope-basin setting, with numerous whole core of wells with full suites of electric logs, high resolution 3D seismic coverage, and 20+ years worth of production data. Sequence stratrigraphic analysis from seismic data combined the lithologic analysis from outcrop analog, core, and well log data helps identify that the Happy Field is located within the transgressive systems tract of the fifth composite sequence in the Leonardian. The reservoir is composed of discrete allochthonous ooid and skeletal grains transported downslope via hyperconcentrated density flows sourced from a re-entrant in the shelf margin and deposited in a long-lived topographic depression at the toe-of-slope. Vertical heterogeneity due to layers of shaley silt punctuated by successive flows of oolitic and skeletal grains along with lateral heterogeneity created by younger flows of material create reservoir compartmentalization which can impede efficient development. Core-calibrated electric log correlations aids in the mapping of isolated compartments which helps with efficient development planning for the field.
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BLACK MANGROVE (AVICENNIA SP.) COLONY EXPANSION IN THE GULF OF MEXICO WITH CLIMATE CHANGE: IMPLICATIONS FOR WETLAND HEALTH AND RESISTANCE TO RISING SEA LEVELS
Rebecca Suzanne Comeaux, M.S. Geo. Sci.
University of Texas at Austin, December 2010
Supervisor: Mead A. Allison
132 pages, 99 references, 6 tables
Populations of black mangroves (Avicennia sp.) are hypothesized to expand their latitudinal range with global climate change in the 21st century, induced by a reduction in the frequency and severity of coastal freezes, which are known to limit mangrove colony extent and individual tree size, as well as an overall warmer climate. The Gulf of Mexico is located at the northward limit of black mangrove habitat and is therefore a prime candidate for population expansion with global warming. This expansion may come at the expense of existing Gulf coastal saline wetlands that are dominantly Spartina spp. marsh grasses. The present study was conducted to focus, not on the extent to date of this replacement, but to examine the potential implications of a marsh to mangrove transition in Gulf wetlands, specifically 1) resistance to accelerating eustatic sea level rise (ESLR) rates, 2) wetland resistance to wave attack in large storms (increased cyclonic storm frequency/intensity is predicted with future climate warming), and 3) organic carbon sequestration and wetland soil geochemistry.
Field sites of adjacent and intergrown Avicennia mangrove and Spartina marsh populations in similar geomorphological setting were selected in back-barrier areas near Port Aransas and Galveston, TX (two sites each) as part of a larger-scale planned study of the full latitudinal transition of the western Gulf funded by the National Institute for Climate Change Research (U.S. Department of Energy). The reconnaissance conducted for site surveys show that black mangrove populations in this part of Texas are clustered near inlet areas, suggesting seed transport vectors are a major control on colony establishment, and likely, on the potential rapidity of wetland habitat replacement. Resistance to ESLR was tested by 1) creating high-accuracy (±1 cm) elevation maps over ~5,000 m2 areas of adjacent mangrove and marsh areas, and 2) measuring mineral and organic matter accumulation rates (Pb/Cs radiotracer geochronology, loss on ignition) from auger cores. Elevation surveys in Port Aransas indicate mangrove vegetated areas are 4 cm higher in elevation than surrounding marsh on an average regional scale, and 1 to 2 cm higher at the individual mangrove scale: at the Galveston sites, any trend is complicated by the area's pre-existing geomorphology and the relative youth of the mangrove colonies. 137Cs accumulation rates and loss on ignition data indicate that mineral trapping is 4.1 times higher and sediment organics are 1.7 times lower in mangroves at Port Aransas; no such definable trends exist at the Galveston sites or in calculated 210Pb sediment accumulation rates. This additional mineral particle trapping in mangroves does not differ in grain size character from marsh mineral accumulation. Elevation change may also be effected by root volume displacement: live root weight measurements in the rooted horizon (~0 to 20 cm depth) are consistently higher in mangrove cores from Port Aransas and the site at the west end of Galveston Island. Port Aransas porosities are lower in mangrove rooted horizons, with a corresponding increase in sediment strength (measured by shear vane in the cores), suggesting mangrove intervals may be more resistant to wave-induced erosion during storm events. Port Aransas mangroves exhibit higher pore water redox potentials and salinities over entire core depths and depressed pH over rooted intervals, suggesting a distinct diagenetic environment exists relative to marsh sites. Increased salinities and higher redox potentials may be a function of the rooting network, which introduces oxygen into the sediment and focuses evapo-transpiration and salt exclusion within this zone: this may prove advantageous when competing with marsh grasses by elevating salinities to levels that are toxic for Spartina. Trends observed in the more mature systems of Port Aransas are generally absent at the Galveston sites, suggesting the youth and physically shorter stature of these systems means they have not yet established a unique sediment signature.
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GEOBAROMETRY FROM RAMAN MICROSPECTROMETRY OF QUARTZ INCLUSIONS IN GARNET: AN EVALUATION
Casey Leigh Corbin, B.S.
University of Texas at Austin, May 2010
Supervisor: William D. Carlson
110 pages, 14 references, 3 tables
Laser Raman microspectrometry was applied to metamorphic quartz inclusions in garnet from three localities, the Picuris Mountains, New Mexico (550 °C, 0.45 GPa); Passo del Sole, central Swiss Alps (560 ± 30 °C, 0.85 ± 0.05 GPa); and the aureole of the Makhavinekh Lake Pluton, Labrador (825 °C, 0.8-1.0 GPa), in order to determine the precision and accuracy of Raman microspectrometry as a geobarometer and its applicability over a wide range of metamorphic conditions. The three main Raman peaks of a quartz inclusion, which is completely enclosed in garnet, shift relative to a quartz standard when a residual pressure on the inclusion is present. This residual pressure is a result of the changes in volume of both the quartz inclusion and the garnet during the exhumation and cooling of the metamorphic rock. This residual pressure can be quantified using a calibration of its relationship to the peak shift and then, using an elastic strain model, the entrapment pressure can be calculated.
Each of the localities that were analyzed in this study has metamorphic conditions that are well-constrained by conventional barometry and thermometry. The data collected in this study were compared to the previously determined values. Additionally, a single quartz inclusion was measured repeatedly to determine the internal precision of this technique.
A set of 17 measurements on a single inclusion produced entrapment pressures for which the standard deviation is 0.20 GPa, indicating limited precision for this technique. Nine quartz inclusions were measured from the Picuris Mountains and have calculated entrapment pressures that range from 0.06 to 0.80 GPa. Eight quartz inclusions were measured from Passo del Sole and have calculated entrapment pressures that range from 0.55 to 1.06 GPa. Eleven quartz inclusions were measured from the aureole of the Makhavinekh Lake Pluton and have calculated entrapment pressures that range from -2.39 to 0.75 GPa.
The spread of values above and below the expected entrapment pressures for measured quartz inclusions from the Picuris Mountains and Passo del Sole may be due to factors that are unaccounted for by this technique, in addition to the quantified imprecision of the technique of 0.20 GPa. Such deviations from the expected values for entrapment pressure might be due to partial release of compressional stress that occurred during cutting of the thin section, or to inclusions whose shape is different from the spherical shape assumed by the elastic-strain model. In the samples from the aureole of the Makhavinekh Lake Pluton, the highly scattered distribution and negative values can be interpreted as evidence that some quartz inclusions from this locality were entrapped by garnet as a-quartz. This finding identifies a limitation to the applicability of this technique: it appears to be inapplicable to rocks that experienced metamorphism at or above the a-ß-quartz transition.
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TEMPORAL AND SPATIAL VARIABILITY OF CAVE-AIR CARBON DIOXIDE IN CENTRAL TEXAS, USA
Brian Davis Cowan, M.S. Geo. Sci.
University of Texas at Austin, May 2010
Supervisor: Jay L. Banner
113 pages, 64 references, 9 tables
There is the potential for bias in the speleothem paleoclimate record due to fluctuations in speleothem growth. A previous study in three central Texas tourist caves has shown that speleothem calcite growth rates vary seasonally in response to density-driven fluctuations in cave-air CO2. Three undeveloped caves and three tourist caves in central Texas were monitored to determine 1) if seasonal CO2 fluctuations are unique to the tourist caves that have been impacted by anthropogenic activity, 2) the extent to which cave-air CO2 concentrations are controlled by natural variations in cave geometry, host rocks, cave volume and overlying soils and 3) how variable cave-air CO2 concentrations are on shorter timescales such as diurnal timescales or in response to storm events. Nearly 150 lateral transects into six caves (three tourist caves and three undeveloped caves) over three years show that CO2 concentrations vary seasonally in five of the caves with peak concentrations in the warmer months and lower concentrations in the cooler months. These seasonal CO2 fluctuations occurred independent of cave volume, geometry, the amount of visitation, and overlying soil thickness.
Nearly 30,000 measurements taken using logging CO2 meters over two years reveal that all caves monitored experienced large diurnal cave-air CO2 fluctuations that can be accounted for by diurnally fluctuating barometric pressure. Typical diurnal CO2 fluctuations in the undeveloped caves were 10,000-15,000 ppm and in the tourist caves 500-1,500 ppm. Air speed measurements taken at two caves confirm that large volumes of air flow into and out of the caves in response to diurnal barometric pressure fluctuations. At one cave 0.95 cave volumes exited the cave during one “exhalation” lasting 7.75 hours and at the other over 15 cave volumes during one “exhalation” lasting 8.83 hours.
Previous cave ventilation studies have treated caves as independent systems that do not exchange gases with the surrounding epikarst; however, we present a conceptual model of airflow through epikarst in which significant subsurface airflow occurs not only in caves, but also through the fractures and dissolution cavities that are typically connected to the caves. This is the only mechanism that can account for the large volume of air flowing into and out of the caves on a diurnal basis and the magnitude and timing of cave air CO2 fluctuations in response to changes in barometric pressure. These results suggest that some speleothem records might be biased due to cave ventilation. This is a serious and poorly recognized source of error in many speleothem paleoclimate records. Diurnal and seasonal cave ventilation may also lead to increased temporal resolution in the speleothem record if diurnal or seasonal layers of calcite are deposited.
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THE COMPARATIVE OSTEOLOGY AND PHYLOGENETIC RELATIONSHIPS OF LEPIDOSIRENID LUNGFISHES
Katharine Elizabeth Criswell, M.S.Geo.Sci.
University of Texas at Austin, May 2011
Supervisor: Christopher J. Bell
250 pages, 101 references, 4 tables
Lepidosirenidae is a clade of freshwater lungfishes that comprise the South American Lepidosiren paradoxa and four African species of the genus Protopterus. These two genera have been geographically separated since the Early Cretaceous break-up of Gondwana, but they share similar biology and skeletal morphology. The lepidosirenid species traditionally were distinguished by a combination of features such as head-to-body ratios, the number of pairs of vertebral ribs, and the presence or absence of external gills, but there are no published discrete skeletal characteristics and no published comparative studies including all extant species.
I used High Resolution X-Ray Computed Tomography (CT), X-Ray photography, and alcohol-preserved, cleared-and-stained, and dry skeletal specimens from museum collections to describe the skeletal morphology of all species of lepidosirenid lungfishes in a comparative context. I digitally disarticulated the bones in each CT scan to compile a comprehensive comparative atlas of the cranial and pectoral elements of all extant lungfish. I discovered that the anocleithrum in Lepidosiren paradoxa, which was previously thought to be lacking, is actually present. I also identified skeletal differences between species in the frontoparietal, parasphenoid, supraorbital, and suboperculum. I incorporated those characters into the first morphological phylogenetic analysis to determine the interrelationships of the lepidosirenids. I also used previously published molecular sequence data from the ribosomal RNA gene 16s to run combined morphological and molecular phylogenetic analyses. To generate phylogenetic hypotheses using different types of data and different methods of determining phylogeny, I employed the maximum parsimony, maximum likelihood, and Bayesian inference methods.
Lepidosirenidae is monophyletic in almost all analyses, Protopterus is monophyletic in each analysis, and Protopterus annectens and Protopterus aethiopicus are sister taxa in every analysis. The phylogenetic positions of Protopterus dolloi and Protopterus amphibius are incongruent in many of the analyses, which indicates that further examination of the skeletal variation and addition of molecular sequences of different genes is needed. Based on the comparative morphological atlas and the phylogenetic analyses, questions of lepidosirenid biogeography, morphological variation within lungfish, and better identification of lungfish fossils can now be investigated in a more rigorous context.
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EPITAXIAL NUCLEATION OF GARNET IN CORONAL METAGABBROS FROM THE ADIRONDACK MOUNTAINS, NEW YORK
Edward A. Cross III, B.S.
University of Texas at Austin, May 2011
Supervisor: William Carlson
56 pages, 38 references, 2 0tables
In granulite-facies metagabbros of the Adirondack Mountains, New York, olivine and plagioclase reacted to form coronas of garnet, plagioclase, clinopyroxene, and orthopyroxene, in which both reactant and product minerals are preserved. Electron backscatter diffraction analysis reveals a systematic crystallographic relationship between the garnet and the precursor plagioclase from 50 different coronas. One single orientation of garnet in relationship to plagioclase predominates. These data provide direct evidence for epitaxial nucleation of garnet on plagioclase. Four crystallographic relationships occur: (011)Grt || (001)Pl , (101)Grt || (110)Pl, [lll]Grt || [lll]Pl , and (100)Grt 15° subparallel to (010)Pl. Comparing unit-cell misfits at these garnet-plagioclase interfaces sets a minimum lattice misfit of 25%, but domain-matching epitaxy can explain this relationship: periodic displacements at the interface, which die out within a distance of only a few atomic layers from the interface itself, may allow this garnet-plagioclase relationship to produce a low-energy interface, and permit epitaxy to govern the nucleation of garnet in these rocks.
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SAND DISTRIBUTION ALONG SHELF-EDGE DELTAIC SYSTEMS: A CASE STUDY FROM EASTERN OFFSHORE TRINIDAD
Anmar Carolina Davila-Chacon, M.Sc.Geo.Sci
University of Texas at Austin, December 2010
Supervisors: Lesli Wood and Lorena Moscardelli
133 pages, 37 references, 6 tables
The study area is situated along the obliquely converging boundary of the Caribbean and South American plates offshore eastern offshore Trinidad. Major structural elements in the shelf break and deep-water slope regions include normal and counter-normal faults to the south and large transpressional fault zones to the north.
Well logs and biostratigraphic information were analyzed for twenty-four wells in the study area to refine previous depositional environment interpretations.
For purposes of this net sand distribution analysis it was decided to consider the deltaic portion of the shelf transit cycle, against the marine portion of the shelf transit cycle and were named T and R cycles, respectively.
T and R cycles were interpreted based on well log patterns and depositional facies shifts. Six T/R cycles were interpreted within the Pliocene to recent stratigraphic succession and shelf edge trajectories were also mapped for each of these cycles based on earlier stratigraphic correlations. Net-to-gross (NTG) ratios were calculated for each component of the T/R cycles and plotted against total thicknesses and net sand values. In addition, NTG trends were mapped for each interval and analyzed based on their proximity to the corresponding shelf edge.
Mapping of the shelf edge trajectories (SET) revealed that (1) SET migrate northeasterly across the Columbus Basin through time and (2) shelf edge orientations are parallel to the strike of growth faults in the south but deflect to the northeast near the Darien Ridge indicating a strong underlying structural control. The NTG plots and maps also revealed that (1) For T cycles, NTG values never exceed 60% and are inversely proportional to total thickness, (2) For R cycles, NTG values are highly variably ranging from 35% to 90%, (3) NTG values increase as the shelf break is approached and (4) The distribution of NTG ratios is also controlled by accommodation space created by local structures.
The Guiana current is believed to play an important role in the redistribution and reworking of sand in the Columbus Basin.
Aggradation and progradation distances were computed for each interval and the results suggest that the younger Sequences C2 (T-R cycle E) and C3 (T-R cycle F) show a stronger progradational trend than the older C4, C5 and C6. This strong progradational trend might indicate delivery of sand basinwards, while for the older intervals; the aggradational trend suggests an increase in sediment storage.
In long-term scale (1-2 m.y.) the Orinoco Delta seems to behave as an aggradational delta that increases sediment storage due to growth fault and high subsidence rates. However, in the short-term scale, the Orinoco delta seems to behave as a rapid progradational delta, for the younger sequences C2 and C3, where sediment bypass is more likely to occur; and as a rapid aggradational (slow prograding) margin for the older intervals C4, C5 and C6.
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MEASURING DIFFUSION COEFFICIENTS IN SANDSTONES USING LA-ICP-MS
Sarah Doyle, B.S. Hydrogeology/Environmental Geology
University of Texas at Austin, May 2010
Supervisor: John M. Sharp
40 pages, 17 references, 5 tables
The movement of solutes in groundwater is of great interest to researchers because of issues such as groundwater contamination, the movement of chemical tracers, and developing methods for pollutant remediation. In this study, solute transport resulting from diffusion is analyzed using Laser Ablation Inductively Coupled Plasma Mass Spectroscopy, or LA-ICP-MS. Diffusion of solutes into rock matrices is characterized by ion and rock specific diffusion coefficients (Deff). Knowing these values is necessary for quantifying transport. The effect of fracture skins, which commonly are present between fracture conduits and rock matrices, on diffusion is also examined. Values found for Deff for two sandstones, the Breathitt Sandstone and the Hinckley Sandstone, as well as for the fracture skin on the Hinckley Sandstone, allow interesting observations on sandstone aquifers to be made. The average values of Deff for the Breathitt and Hinckley Sandstones are 5.57 x 10-7 cm2/s and 5.735 x 10-7 cm2/s, respectively. The average Deff for a Hinckley sandstone fracture skin is 3.06 x 10-7 cm2/s, which is lower than through the matrix, suggesting the fracture skin impedes diffusion. Factors that could change the results found using this experimental method and LA-ICP-MS are addressed and overall the results of this experiment show this method is an effective alternative to past methods of determining diffusion coefficients.
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THERMAL IMAGING OF MICROBIAL MATS PROVIDES CLUES TO THERMOPHILE COMMUNITY STRUCTURE: EL TATIO GEYSER, CHILE
Anne E. Dunckel, B.S.
University of Texas at Austin, May 2009
Supervisor: Meinhard B. Cardenas
27 pages, 35 references
Microbial mats around thermal springs are a unique laboratory for understanding microbial ecology and biogeochemistry. Microbial mats in these extreme environments display organized community structures that manifest visually through their vibrant color zonation. The advent of portable high-resolution thermal infrared imaging technology opens new opportunities to investigate the role of temperature in microbial community structure. This study uses a thermal infrared camera to measure in situ temperature at an unprecedented level of detail at four hot springs located in the El Tatio Geyser Field of northeastern Chile. Paired temperature maps and visual images show that communities with specific coloration (i.e. RGB values) preferentially occur within specific temperature ranges. Unlike previous studies where maximum, minimum, and optimal temperatures for a given community are based on controlled laboratory studies or limited field temperature measurements, the thermal imaging method allows for mapping thousands of temperature values in a snapshot, rapidly constraining natural temperature values for a given community. This approach will expand current understanding of thermal organization of microbial communities in hot springs and will open doors for detailed analysis of thermal controls in natural microbial environments.
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CORAL-BASED CLIMATE RECONSTRUCTIONS FROM A MASSIVE PORITES CORAL FROM SABINE BANK (VANUATU)
Elizabeth M. Dunn, MSGeoSci
University of Texas at Austin, May 2009
Supervisor: Terrence M. Quinn
107 pages, 21 references, 74 tables
A monthly resolved, 133 year record of coral Sr/Ca variations has been developed from a massive Porites coral that was drilled in the shallow waters of a submerged carbonate platform (Sabine Bank, 15.9°S, 166.14°E) located ~50 km west of Espiritu Santo, Vanuatu. This truly open-ocean site, at which daily measurements of temperature and salinity are available for ~ 6 years, permits the reconstruction of local environmental variability using variations in coral skeletal geochemistry. Coral Sr/Ca-SST variations are well matched to variations in local SST, but bear little relation to changes in local SSS indicating little or no influence of salinity on coral Sr/Ca. The complete coral Sr/Ca-SST time series is characterized by abundant inter-annual variability, a strong trend towards warming (i.e., lower Sr/Ca values) from ~1980-2006. Interannual SSTA variations at Sabine Bank correspond reasonably well to SSTA variations from the central Pacific cool tongue (Niño 3.4 region), indicating that coral Sr/Ca variations record ENSO variability in the region.
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ECONOMETRIC MODELING OF THE IMPACT OF RESIDENTIAL ENERGY EFFICIENCY RETROFITS ON HOME SALE PRICES
Andrew Michael Durkee, M.A. EER
University of Texas at Austin, May 2009
Supervisor: Michael Webber
74 pages, 23 references, 11 tables
Today’s declining housing market combined with rising energy prices presents homeowners with an opportunity to better position their house for sale by reducing the energy costs for future homeowners. Energy efficiency retrofits offer a method for the homeowner to advertise their home in a different manner than the ones around it as well as potentially increase the sale price of the home. This thesis contains an analysis of how home energy efficiency retrofits affect the sale price of a single family residence. To do so, this research uses the following four steps: First, an understanding of the amount of electricity a typical home consumes as well as the retrofits that could be installed to curb this consumption is determined. Second, a review of recent Federal energy policy will be offered in order to understand how the homeowner can introduce energy efficiency retrofits into their home, often times for very little money, but great added value. Third, current home sale data for the Houston, TX area is analyzed to produce a baseline equation for a home that is up for sale. This baseline equation is then modified in order to provide a home seller or buyer with an understanding of the added value of energy efficiency retrofits. Using these equations a user tool is developed in order to allow for the buyer/seller to enter specific housing characteristics into a model as well as energy efficiency retrofits and be presented with the added value they can expect the house to assume. The user tool also allows for a visual representation of a home buyer’s monthly expenditures on a mortgage and electricity use are affected by the installation of energy efficiency retrofits and the price of electricity.
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VARIATION WITHIN THE BONY LABYRINTH OF MAMMALS
Eric Gregory Ekdale, Ph.D.
University of Texas at Austin, December 2009
Supervisor: Timothy Rowe
439 pages, 344 references, 26 tables
The morphological diversity of the external and internal surfaces of the petrosal bone, which contains the structures of the inner ear, across a broad range of therian mammals is documented, and patterns of variation across taxa are identified. One pattern of variation is the result of ontogenetic changes in the ear region, as described for the external surface morphology of a sample of isolated petrosal bones referred to Proboscidea from Pleistocene deposits in central Texas. The morphology of the aquaeductus Fallopii for passage of the greater petrosal branch of the facial nerve supports an ontogenetic explanation for some variation within the proboscidean sample, and a sequence of ossification surrounding the aquaeductus Fallopii is hypothesized. Further ontogenetic patterns are investigated using digital endocasts of the bony labyrinth (preserved on the internal surfaces of the petrosal) constructed from CT data across a growth series of the opossum Monodelphis domestica. Strong correlation between skull length and age is found, but from 27 days after birth onward, there is no correlation with age among most dimensions of the inner ear. Adult dimensions of several of the inner ear structures are achieved before the inner ear is functional in M. domestica. Morphological variation within the inner ear of several eutherian mammals from the Cretaceous of Asia, including zhelestids from the Bissekty Formation of Uzbekistan, is described. The variation within the fossil sample is compared to that observed within extant species of placental mammals, and it is determined that the amount of variation within the Bissekty zhelestid population is within the range of that measured for extant species. Additional evolutionary and physiological patterns preserved within the walls of the bony labyrinth are identified through a high level anatomical comparison of the inner ear cavities across Placentalia as a whole. In particular, features of the inner ear support monophyly of Cetacea, Carnivora, Primatomorpha, and caviomorph Rodentia. The volumetric percentage of the vestibular apparatus (vestibule plus semicircular canals) of aquatic mammals is smaller than that calculated for terrestrial relatives of comparable body size. Thus, aspects of the bony labyrinth are both phylogenetically and physiologically informative.
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RECONSTRUCTING ENVIRONMENTAL FORCINGS ON AEOLIAN DUNE FIELDS: RESULTS FROM MODERN, ANCIENT, AND NUMERICALLY-SIMULATED DUNES
Erin Nancy Eastwood, Ph.D.
University of Texas at Austin, December 2011
Supervisor: Gary Kocurek
156 pages, 120 references
This dissertation combines studies of aeolian bedforms and aeolian dune-field patterns to create a comprehensive set of tools that can be used in tandem (or separately) to extract information about climate change and landscape evolution, and to identify the controls on formation for specific modern dune fields or ancient aeolian sequences. The spatial distribution of surface processes, erosion/deposition rates, and lee face sorting on aeolian dunes are each a function of the incident angle. This correlation between stratification style and incidence angle can be used to develop a "toolbox" of methods based on measurements of key suites of parameters found in ancient aeolian deposits. Information obtained from the rock record can be used as input data for different kinds of numerical models. Regional-scale paleowind conditions can be used to validate paleoclimate and global circulation models. Understanding the natural variability in the Earth's climate throughout its history can help predict future climate change. Reconstructed wind regimes and bedform morphologies can be used in numerical models of aeolian dune-field pattern evolution to simulate patterns analogous to those reconstructed from ancient aeolian systems. Much of the diversity of aeolian dune-field patterns seen in the real world is a function of the sediment supply and transport capacity, which in turn determine the sediment availability of the system. Knowledge of the sediment supply, availability, and transport capacity of aeolian systems can be used to predict the amount of sand in the system and where it might have migrated. This information can be extremely useful for development and production of oil and gas accumulations, where a discovery has been made but the spatial extent of the aeolian reservoir is unknown.
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THE CRANIAL MORPHOLOGY OF AN EXCEPTIONALLY PRESERVED SPECIMEN OF THE LOWER PERMIAN REPTILE CAPTORHINUS AGUTI
Sebastian Egberts, MSGeoSci
University of Texas at Austin, May 2009
Supervisor: Christopher J. Bell
80 pages, 60 references, 1 table, 1 glossy plate
Captorhinus aguti is a Permian eureptile known from localities in Texas and Oklahoma. It is a well known taxon critical to understanding the evolutionary relationships among the major lineages of reptiles and its osteology was intensively studied by several previous authors. I present a new description of an exceptionally preserved skull of Captorhinus aguti, TMM 40882-41, from fissure fill deposits from the Dolese Brother’s Quarry, Oklahoma. I used High-resolution X-ray computed tomography to reveal new anatomical details of the specimen and created a digital three-dimensional model of the skull, as well as 3-D models of the individual bony elements, which served as the basis of this description.
Every bony element in the skull is present as well as elements of the right mandible, but the left mandible is absent. Because most of the skull elements are in situ, detailed three-dimensional reconstructions of the relationships, orientations, and articulations of these elements reveal phylogenetically significant features. For example, the septomaxilla is more complex than previous authors suggested. The lateral side features a large septomaxillary canal, which is a direct anterior extension of the lacrimal duct. Previously described as a synapomorphy of synapsid reptiles, its presence in Captorhinus indicates that this was ancestral to amniotes. Additionally, the ventral surface of the septomaxilla may feature another large foramen.
Other newly described morphologies include the sphenethmoid, which is almost completely preserved. The sphenethmoid is goblet-shaped in cross-section and is dorsally broader than previously assumed. I was also able to reconstruct the first endocast of the Meckelian canal and associated passages for vessels of Captorhinus aguti in great detail, owing to the almost perfect articulation of the mandible. The Meckelian canal innervates primarily the lateral surface, indicating a supply of touch-sensors.
These new discoveries in the skull morphology of Captorhinus aguti contribute important morphological characters for phylogenetic hypotheses of the relationships within captorhinids. This is especially valuable because this species is the most common captorhinid included in prior phylogenetic analyses. My work will aid in future studies that seek to resolve the relationships among all amniotes.
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STRATIGRAPHIC ARCHITECTURE AND EUSTATIC SETTING OF SLOPE GRAINSTONES ASSOCIATED WITH PEAK ICEHOUSE CONDITIONS
Joseph Assaad El-Azzi, M.S. GeoSci
University of Texas at Austin, May 2010
Supervisor: Charles Kerans
100 pages, 69 references, 7 tables
High-latitude Gondwanan glaciation is widely recognized during Late Pennsylvanian and Early Permian (Wolfcampian) time. Accompanying high-amplitude glacioeustatic fluctuations (up to 120m) have been documented from North American midcontinent cyclothems and southwestern shelf-margin carbonates. Complex stratal architectures and facies juxtapositions are commonly associated with such settings. Autochthonous lowstand prograding wedge deposits of shallow shelf origin can generate stratal architectures that superficially resemble those of deeper water allochthonous slope facies.
This study uses outcrop data collected from the Southern Outlier of the Hueco Mountains to provide documentation of deposit types and architectures observed on a platform margin and slope setting. Data collected for this study include traditional measured section, hand sample, and petrographic thin section analysis. Ten detailed measured sections were logged and surveyed with RTK-GPS in order to allow integration with ground-based LIDAR data. Key sequence stratigraphic surfaces and geobody boundaries were mapped on photomosaics and spatially constrained using RTK-GPS and later are integrated into a geo-referenced LIDAR pointcloud dataset. A 3D geocellular model was constructed using upper and lower bounding surfaces to define zones and subsequently the LIDAR points with assigned facies attributes were used to distribute facies within the cells of each of the defined zones.
A constructed depositional model reveals five depositional environments 1) toe of slope to basin, 2) lower slope 3) middle slope, 4) upper slope and 5) platform edge. Mud-dominated fabrics compose much of the lower slope to basin environments represented by low-energy fine-grained gravity settling deposits. Intermittent grain-dominated fabrics in form of turbidites are deposited within the lower slope. Matrix-supported lithoclastic debris flow type deposits form backfilling aprons on the middle slope. Grain-dominated grain flows develop stacked shingled wedges within the middle slope. Karsted breccias mark a depositional hiatus formed by subaerial exposure and significant erosion on the slope. Boundstone fabrics within tabular and mounded algal buildups mark the platform edge environments. These superimposed deposits are interpreted to record an overall regression from the toe-of-slope to the middle slope capped by a subaerially exposed surface marking a depositional hiatus followed by a transgression to the platform margin.
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FRACTURE DEVELOPMENT AND DIAGENESIS OF THE TORRIDONIAN APPLECROSS FORMATION, NORTHWEST SCOTLAND
Magdalena Alyssa Ellis, M.S. Geo Sci
University of Texas at Austin, August 2009
Supervisor: Stephen E. Laubach
341 pages, 172 references, 12 tables
Late Proterozoic Torridonian Applecross Sandstone, exposed west of the Paleozoic Moine Thrust Zone (MTZ) in the Northwest Highlands of Scotland, preserves fractures sets that reflect a 900 m.y. structural history. The Applecross Sandstone contains at least three systematically developed sets of fractures, A, B and L. Relative timing was determined by crosscutting relations. The oldest fractures, Set A, strikes north-south and is completely filled with quartz cement. These formed as opening-mode fractures, indicated by crack-seal texture along fracture walls, and later experienced reactivation as strike slip faults, as indicated by brecciated fracture fill. Set B has a tri-modal distribution in orientation and contains clear, unbrecciated quartz. Set B reflects distributed MTZ-related deformation in the foreland; the three subsets, Bx, By, Bz, are oriented as conjugates, front-normal, and front-parallel fractures to the Paleozoic Moine Thrust Zone.
The youngest fractures, Set L, displays strikes ranging from NE to ESE. Although Set L fractures appear barren at the outcrop scale microscopy reveals they have a thin veneer of quartz. This fracture set is spatially and kinematically related to many small-displacement faults in the region that offset the Applecross, the overlying Cambrian Eriboll Formation, and the MTZ. Set L fractures increase in intensity by as much as an order of magnitude as faults are approached. Moreover, Set L is arranged into hierarchies of splay fractures. The sense of movement implied by splay fracture patterns is the same as that of the small faults. The growth and evolution of this fault and fracture system involves producing splay fractures at a range of orientations and scales in a 2 to 10 m wide halo of damage around the faults.
The style of fault-related deformation in the Applecross Sandstone contrasts markedly with that of the overlying Cambrian Eriboll Formation (a quartzose marine sandstone), which is more fractured and displays patchy patterns with respect to the fault-related fractures (Set L), rather than the halo-like patterns observed in the Applecross. The Applecross and Eriboll differ in composition (subarkose vs. quartzarenite), mechanical layer thickness (>tens of meters vs. centimeters), mechanical properties, and propensity for fractures to seal readily in the quartzose Eriboll compared to the lithic and feldspar-rich Applecross, where quartz cement growth is impaired by the widespread presence of non-quartz substrate on fracture walls.
I used point counting methods and rock mechanical property tests to characterize the rock mass and diagenetic history of the Applecross. The feldspar and clay mineral rich Applecross may represent a lithology that is resistant to fracturing. I also used high resolution scanning electron microscopy with cathodoluminescence (CL), scanline methodologies, and field fracture mapping to characterize the fracture cement textures and size scaling attributes of the fracture sets.
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ECONOMIC ANALYSIS OF WIND AND SOLAR ENERGY SOURCES OF TURKEY
Mehmet Erturk, M.A.
University of Texas at Austin, May 2011
Supervisor: Christopher J. Jablonowski
166 pages, 98 references, 99 tables
Renewable energy sources have become very popular in the last years in electricity generation thanks to the technological developments, the increase in the price of fossil fuels and the environmental concerns. These factors have also prompted Turkey to utilize her very rich renewable energy sources to meet the demand increasing around 7% annually. In this study, solar and wind energy potential of Turkey is analyzed in terms of its economics to find out whether these sources are real alternatives to fossil fuels in electricity generation. Before this analysis, wind and solar energy technologies and costs and wind and solar energy potential of Turkey are discussed. Then, we set up models to calculate cash flows which are used to calculate payback, NPV, IRR, LCE and shut-down price to conduct economic analysis for five technologies which are onshore wind, offshore wind, solar PV, solar trough and solar tower technologies. In addition to base case scenario, we carry out uncertainty analysis for the most promising technologies which are onshore wind and solar tower technologies by evaluating NPV and LCE under uncertain environment. The main finding of these analyses is that only onshore wind projects are feasible and attractive in Turkey; none of other technologies is economically feasible. However, with a minor increase in the regulated price for solar thermal electricity, tower plant projects will also be feasible.
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AEOLIAN DUNE-FIELD BOUNDARY CONDITIONS AND DUNE INTERACTIONS RELATED TO DUNE-FIELD PATTERN FORMATION ON EARTH AND MARS
Ryan C. Ewing, PhD
University of Texas at Austin, December 2009
Supervisor: Gary Kocurek
117 pages, 114 references, 2 tables
Aeolian dune fields form some of the most striking patterns on Earth and Mars. These patterns reflect the internal dune dynamics of self-organization within boundary conditions, which are the unique set of environmental variables within which each dune field evolves. Dune-field pattern self-organization occurs because of interactions between the dunes themselves and the rich diversity of dune-field patterns arises because boundary conditions alter the type and frequency of dune interactions. These hypotheses are explored in three parts. First, source-area geometry and areal limits are two newly recognized boundary conditions. Measurements of crest length and spacing from satellite images of dune patterns with point and line source-area geometries show an increase in crest length and spacing over distance, whereas crest length and spacing in plane-sourced patterns emerge equally across the dune field. The areal limit boundary condition is the size and shape of the dune field itself. Empirical measurements from ten dune fields ranging over four orders of magnitude in area show that spacing increases and defect density decreases as the area of the dune field increases. A simple analytical model indicates that dune fields that are five times longer in the dune migration direction can achieve the greatest spacing for a given area. Second, time-series aerial photographs and airborne LiDAR show that fully developed, crescentic aeolian dunes at White Sands, New Mexico, interact and the dune pattern organizes in systematically similar ways as wind ripples and subaqueous dunes and ripples. Interaction type, classified as constructive, regenerative or neutral in terms of pattern development, changes spatially with the pattern because of the imposition of the line-source area and sediment-availability boundary conditions. Upwind dominance by constructive interactions at the field line-source yields to neutral and regenerative interactions in the sediment availability-limited field center. Third, the dune-field pattern in the Olympia Undae Dune Field on Mars is comprised of two generations of dunes. This scenario of pattern reformation with a new wind regime shows that the emergence of the younger pattern is controlled by the boundary condition of the antecedent dune topography imposed upon the interaction between the younger and older patterns.
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NATURAL FRACTURE CHARACTERIZATION OF THE NEW ALBANY SHALE, ILLINOIS BASIN, UNITED STATES
Lucas Jared Fidler, M.S. Geo Sci
University of Texas at Austin, December 2011
Supervisors: Stephen E. Laubach and Julia F.W. Gale
291 pages, 216 references, 20 tables
The New Albany Shale is an Upper Devonian organic-rich gas shale located in the Illinois Basin. A factor influencing gas production from the shale is the natural fracture system. I test the hypothesis that a combination of outcrop and core observations, rock property tests, and geomechanical modeling can yield an accurate representation of essential natural fracture attributes that cannot be obtained from any of the methods alone.
Field study shows that New Albany Shale outcrops contain barren (free of cement) joints, commonly oriented in orthogonal sets. The dominant set strikes NE-SW, with a secondary set oriented NNW-SSE. I conclude that the joints were likely created by near-surface processes, and thus are unreliable for use as analogs for fractures in the reservoir. However, the height, spacing, and abundance of the joints may still be useful as guides to the fracture stratigraphy of the New Albany Shale at depth. The Clegg Creek and Blocher members contain the highest fracture abundance.
Fractures observed in four New Albany Shale cores are narrow, steeply-dipping, commonly completely sealed with calcite and are oriented ENE-WSW. The Clegg Creek and Blocher members contain the highest fracture abundance, which is consistent with outcrop observations. Fractures commonly split apart along the wall rock-cement interface, indicating they may be weak planes in the rock mass, making them susceptible to reactivation during hydraulic fracturing.
Geomechanical testing of six core samples was performed to provide values of Young's modulus, subcritical index, and fracture toughness as input parameters for a fracture growth simulator. Of these inputs, subcritical index is shown to be the most influential on the spatial organization of fractures. The models predict the Camp Run and Blocher members to have the most clustered fractures, the Selmier to have more evenly-spaced fractures, and the Morgan Trail and Clegg Creek to have a mixture of even spacing and clustering.
The multi-faceted approach of field study, core work, and geomechanical modeling I used to address the problem of fracture characterization in the New Albany Shale was effective. Field study in the New Albany presents an opportunity to gather a large amount of data on the characteristics and spatial organization of fractures quickly and at relatively low cost, but with questionable reliability. Core study allows accurate observation of fracture attributes, but has limited coverage. Geomechanical modeling is a good tool for analysis of fracture patterns over a larger area than core, but results are difficult to corroborate and require input from outcrop and core studies.
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OFFSHORE MAPPING AND MODELING OF MIOCENE-RECENT EXTENSIONAL BASINS ADJACENT TO METAMORPHIC GNEISS DOMES OF THE D'ENTRECASTEAUX ISLANDS, EASTERN PAPUA NEW GUINEA
Guy Gregory Fitz, M.S. Geo. Sci.
University of Texas at Austin, August 2011
Supervisor: Paul Mann
183 pages, 98 references, 5 tables
The D'Entrecasteaux Island (DEI) gneiss domes are fault-bounded domes with ~2.5 km of relief exposing ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic gneisses and migmatites exhumed in an Oligocene-Miocene arc-continent collision and subduction zone subject to Late Miocene to Recent continental extension. To study the style of continental extension accompanying exhumation of the DEI gneiss domes, a grid of 1,518 km of 2-D multi-channel seismic (MCS) reflection data and well data is interpreted from the offshore areas surrounding the DEI, including the Trobriand basin and the Goodenough basin. The offshore study is combined with onshore geologic information to constrain the area's Oligocene to Recent basinal and tectonic evolution.
MCS and well data show the Trobriand basin formed as a forearc basin caused by southward Miocene subduction at the Trobriand trench. Late Miocene basin inversion uplifted the southern and northern basin margins. Subduction slowed at ~8 Ma as the margin transitioned to an extensional tectonic environment. Since then, the Trobriand basin has subsided 1-2.5 km as a broad sag basin with few normal faults deforming the basin fill.
South of the DEI, the Goodenough rift basin developed after extension began (~8 Ma) as the hanging-wall of the north-dipping Owen-Stanley normal fault bounding the southern margin of the basin. Rapid uplift of the adjacent footwall of the Owen-Stanley fault zone in the Papuan Peninsula accompanied the formation of the Goodenough submarine rift basin.
The lack of upper crustal extension accompanying subsidence in the Trobriand and Goodenough basins suggests depth-dependent lithospheric extension from 8-0 Ma has accompanied uplift of the DEI gneiss domes. Structural reconstructions of seismic profiles show 2.3 to 13.4 km of basin extension in the upper crust, while syn-rift basin subsidence values indicate at least 20.7 to 23.6 km of extension occurred in the lower crust since ~8 Ma. Results indicating thinning is preferentially accommodated in the lower crust surrounding the DEI are used to constrain a schematic model of uplift of the DEI domes involving vertical exhumation of buoyant, post-orogenic lower crust, far-field extension from slab rollback, and an inverted two-layer crustal density structure.
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SEQUENCE STRATIGRAPHY, SANDSTONE ARCHITECTURE, AND DEPOSITIONAL SYSTEMS OF THE LOWER MIOCENE SUCCESSION IN THE CARANCAHUA BAY AREA, TEXAS GULF COAST
Rattanaporn Fong-Ngern, MSGeoSci
University of Texas at Austin, August 2011
Co-Supervisors: William L. Fisher and William A. Ambrose
108 pages, 47 references, 3 tables
This study defines depositional environments and constructs the sequence stratigraphic framework of the lower Miocene Oakville Formation and the basal part of the middle Miocene Lagarto Formation in the Carancahua Bay area. The Early Miocene of the northwestern Gulf of Mexico represents a tectonically stable period with a high sediment influx.
The analysis is based on a data set composed of 45 well logs and 200 mile2 area 3D seismic volume. The study interval was divided into five depositional sequences 1-5 that encompass 0.6-2.5 My. LST, TST, and HST systems tracts were recognized by stacking patterns and bounding surfaces. Sequence thickness increases from sequence 1 to 3 and displays reverse thickness trends from sequence 3 to 5, implying changes in accommodation space relative to sediment supply, beginning with high rates of accommodation and evolving into low accommodation rates relative. Besides type-1 depositional sequence which forms during relative sea-level fall below the shoreline break, regressive units of T-R sequence model were also defined and delineated. The interval contains four regressive units, R-Unit1-4. The R-Unit net sandstone maps exhibit the same characteristic of a dip-oriented source of delta-plain origin and a delta-front depocenter basinward.
Integration of well log patterns, sandstone dispersal trends from net sandstone maps and seismic stratal slices led to interpretation of depositional environments in each sequence. LST deposits are represented mainly by incised-valley fill facies. TSTs are composed predominantly of retrogradational barrier/tidal-inlet facies, whereas other TSTs contain lagoonal and reworked deltaic systems. HST1 is composed mainly of fluvial-dominated deltaic systems, whereas deltaic systems in other HSTs exhibit wave-influenced deltaic and strandplain depositional systems. The integrated methodology reveals depositional facies variations in contrast to previous work that interpreted these deposits as shorezone systems.
During LSTs coarse-grained sediments bypassed shelf through incised valley systems to a downdip depocenter. More sandy sediments were stored on shelf as deltaic and strandplain deposits during HSTs. In contrast to the others, destructive process occurred in TSTs and reworked sandy sediments, for example from delta fronts to barrier bar and lagoonal facies. Submarine fans form by sediments transported through incised-valley systems and delta fronts are commonly good reservoirs. Hence, presence of such depositional facies in the study area might be genetically linked to exploration targets.
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TRADE-OFFS IN ELECTRICITY PLANNING IN MEXICO
Andrés Gallardo, MA
University of Texas at Austin, August 2011
Supervisors: Charles Groat and Michelle Foss
97 pages, 47 references, 31 tables
Electricity generation is a vital element of economic growth, and it is necessary to encourage a growth model that does not endanger the capacity of a country to generate electricity.
Generating electricity entails costs. This cost is not only economical but can also be, for example, environmental. This implies that there are different trade-offs associated with choices about how to generate electricity, such as technologies, fuels, impact on the environment, construction costs, budget constraints and so on.
The Federal Government owns Mexico's electricity sector. As such not only does it write the rules of the electricity sector but also executes these rules. The government has stated a series of guiding principles regulating the electricity sector. These guiding principles reflect the priorities that should be taken into account when designing electricity portfolios.
My thesis uses financial tools to offer a new approach to the problem of developing electricity portfolios. I assume that the electricity generation mix can be seen as a portfolio of assets. Using portfolio management techniques, I demonstrate scenarios for efficient portfolios given key assumptions about generation choices and prevailing costs. I also illustrate the implications of prioritizing one guiding principle over the other in terms of portfolio cost.
Finally, my use of a portfolio modeling approach highlights the complexities inherent in public policy making given the technical and cost-driven nature of the electric power businesses and value chains. My work provides a possible method for more productive evaluation of various approaches in light of mixed priorities and the broad diversity of stakeholders in Mexico.
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OUTCROP-CONSTRAINED FLOW AND TRANSPORT MODELS OF REFLUX DOLOMITIZATION
Beatriz Garcia-Fresca, Ph.D.
University of Texas at Austin, December 2009
Supervisors: F. Jerry Lucia and John M. Sharp Jr.
180 pages, 157 references, 2 tables
Two hydrogeologic models explore reflux dolomitization using two outcrop datasets at different scales to constrain transient boundary conditions and heterogeneous petrophysical properties. A platform-scale petrophysical model of the Permian San Andres Formation was built from outcrop and subsurface data following a reservoir modeling approach that preserves outcrop heterogeneity and incorporates a sequence stratigraphic framework. This model was used as input for hydrogeological simulations of hypersaline fluid flow and solute transport during the accumulation and compaction of the platform. Boundary conditions change over time, as relative sealevel fluctuations drive sedimentation, depositional environment migration, topographic gradients, and location, size and salinity of the brine source. The potential volume and distribution of dolomite formed is inferred by a magnesium mass-balance. The composite result of reflux events at various orders of stratigraphic hierarchy is a complex dolomite pattern that resembles that observed on San Andres outcrops. Dolostone bodies across the platform may be generated by different combinations of favorable conditions, including proximity to the brine source, zones of higher permeability, permeability contrasts, and latent reflux.
A meter-scale reactive transport model of the Albian Upper Glen Rose Formation simulates deposition of three high-frequency cycles punctuated by three brine reflux events. The simulator determines flow, solute and reactive transport along the flow paths, revealing the spatial and temporal distribution of calcite dissolution, and precipitation of dolomite and sulfate. The model recreates fully and partially dolomitized cycles within the time and lithological constrains on Glen Rose outcrops. Our results show that the distribution of dolomite within a high-frequency cycle may be the net result of intercycle processes, whereby dolomitizing fluids sourced from younger cycles flow across stratigraphically significant boundaries. We also show that variations in dolomite abundance and the unfulfilled dolomitization potential control the contemporaneous propagation of multiple dolomite fronts and the coalescence of discrete dolomite bodies.
Results show that reflux is an effective and efficient mechanism to dolomitize carbonate formations that progresses simultaneously with sediment accumulation. Dolomitization is the cumulative result of many short-lived reflux events, sourced in different locations and times, and amalgamation of successive dolostone bodies. This model contrasts with previous studies that approached dolomitization of a carbonate platform as a discrete reflux event and current interpretations that relate dolomite bodies to their most immediate stratigraphic surfaces.
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KARST HYDROGEOLOGY AND SPELEOGENESIS OF SISTEMA ZACATÓN, TAMAULIPAS, MEXICO
Marcus Orton Gary, Ph. D.
University of Texas at Austin, December 2009
Supervisor: John M. Sharp, Jr.
232 pages, 182 references, 7 tables
Understanding geologic mechanisms that form karst is of global interest. An estimated 25% of the world’s population obtains water from karst aquifers and numerous major petroleum reserves are found in paleokarst reservoirs, so characterization and classification of specific types of karst is essential for resource management. Sistema Zacatón, which includes the second deepest underwater cave in the world, is hypothesized to have formed from volcanogenic karstification, defined as a process that relies on four components to initiate and develop deep, subsurface voids: a carbonate matrix, preferential groundwater flowpaths (fractures), volcanic activity that increases groundwater acidity, and groundwater flux through the system. Phases of karstification creating this modern hydrogeological environment are defined using numerous methods: field mapping, 3-D imaging of surface and aqueous environments, geophysical investigations, physical and chemical hydrogeologic characterization, and microbial analysis. Interpretation of the results yields a multi-phased speleogenetic model of the karst, with most phases occurring in the late Pleistocene. The surface rocks are carbonate travertine with Pleistocene mammoth fossils found within the rock matrix, and are interpreted as a hydrothermal travertine terrace formed as nearby volcanic activity peaked, thus representing the end member of a carbonate mass transfer system originating deep in the subsurface. The modern karst system includes a dynamic set of deep, phreatic sinkholes, also called cenotes, which propagated up through the travertine, eventually exposing hydrothermal water supersaturated with carbon dioxide to the atmosphere. In some cases these cenotes have precipitated seals of a second stage of travertine as CO2 degassed, capping the sinkhole with a hydrologic barrier of travertine. Evidence of these barriers is observed in aqueous physical and geochemical characteristics of the cenotes, as some have high hydrologic gradients and contrasting geochemistry to those of neighboring cenotes. Investigations of electrical resistivity geophysics and underwater sonar mapping support the hypothesis of the barriers and define the morphology in intermediate and final phases of sinkhole sealing. Volcanogenic karstification is not limited to Sistema Zacatón, although the localized nature coupled with rapid and extreme degrees of karstification makes it an ideal modern analogue for classifying other karst systems as volcanogenic.
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THE INFLUENCE OF PRE-ERUPTIVE STORAGE CONDITIONS AND VOLATILE CONTENTS ON EXPLOSIVE FRAGMENTATION OF MAFIC PLINIAN ERUPTIONS
Katherine Goepfert, MSGeoSci
University of Texas at Austin, May 2009
Supervisor: James Gardner
101 pages, 74 references, 5 tables
Explosive (Plinian/sub-Plinian) mafic eruptions are rare in the geologic record and very little is known about what triggers them. This study focuses on the pre-eruptive storage conditions (pressure, temperature, and viscosity) and the concentrations of volatiles dissolved in two of the largest known mafic Plinian eruptions: the 122 B.C. eruption of Mt. Etna and the Pleistocene Fontana Lapilli. Are unusually high viscosities and/or volatile contents responsible for this style of behavior? Melt inclusions in plagioclase and 23 hydrothermal experiments were analyzed to constrain dissolved water concentrations and pre-eruptive temperature and pressure conditions. The 122 B.C. Etna hawaiitic melt had 0.09-2.77 wt.% H2O dissolved in the magma, a temperature of 1010 ±10 oC, and a minimum pressure of 50-65 MPa. The Fontana Lapilli contained 0.84-2.82 wt.% H2O, had a pre-eruptive temperature of 1035 ±25 oC, and had a minimum pressure of 25-70 MPa. These pre-eruptive conditions were used to calculate viscosity at fragmentation of 5 x 105 Pa s for the 122 B.C. Etna eruption and 470 Pa s for the Fontana Lapilli. High percentages of microlites and greater dissolved volatile contents are common for the less intense eruptions of Mt. Etna. The water concentrations for the Fontana eruption are much lower than those of nearby volcanoes with less explosive eruptions. A possible mechanism for these mafic Plinian eruptions is an overpressure in the storage area and/or sudden decompression causing the melt rise unusually fast to reach a critical porosity threshold.
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CLASTIC WEDGE DEVELOPMENT AND SEDIMENT BUDGET IN A SOURCE-TO-SINK TRANSECT (LATE CAMPANIAN WESTERN INTERIOR BASIN, SW WYOMING AND N COLORADO)
Carolina Andrea Gomez, PhD
University of Texas at Austin, December 2009
Supervisor: Ron J. Steel
The problem of how sand and mud was distributed downslope, within linked alluvial-brackish water-marine shoreline systems of an extensive clastic wedge is addressed here. The Iles Clastic wedge accumulated over a time period of a few million years (my), and its component high-frequency regressive-transgressive sequences have a duration of a few 100 thousand years (ky). The sediment partitioning study provides insight into where the thickest sandstones and mudstones were located, and generates a model that can be applied to improving the management of hydrocarbons or water resources. A 300 km 2-D study transect across the Iles Clastic Wedge in SW Wyoming and N Colorado included subsurface well log information and outcrop stratigraphic columns. This information was used to correlate high-frequency sequences across several hundred kilometers, characterize depositional processes from proximal to distal reaches, develop a sediment partitioning model, and understand the role of the likely drivers in the development of the wedge and its internal sequences. The main results of this study are:
(1) The Iles Clastic Wedge spans 3 my (500 m thick) and is composed internally of 11 sequences of 200-400 ky, each of which have significant regressive-transgressive transits of up to 90 km. Sediment partitioning analysis shows that within the regressive limb of the large wedge, the component regressive compartments tend to thicken basinwards, whereas transgressive compartments thicken landwards. This geometry is driven by preferential erosion in proximal areas during regression, bypassing much sediment to the marine shorelines, and transgressive backfilling into proximal areas previously eroded more deeply.
(2) The greatest concentration of sands tends to be located in the proximal fluvial and estuarine facies of the transgressive compartments and within the medial shoreline/deltaic facies of the regressive compartments.
(3) As the high-frequency sequences developed, the effectiveness of basinward sand partitioning reaches a maximum value near the peak regression level of the wedge, reflecting stronger erosion and sediment bypass during this times.
(4) The development of the Iles Clastic Wedge was influenced by both tectonic and eustatic drivers, with important tectonic control in the upstream reaches. On a 4th-order timescale, the Iles Wedge internal sequences were likely influenced mainly by eustasy.
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CORAL-BASED RECONSTRUCTION OF SURFACE SALINITY AT SABINE BANK, VANUATU
Meaghan Kathleen Gorman, MSGeoSci
University of Texas at Austin, May 2011
Supervisor: Terrence M. Quinn
55 pages, 25 references, 1 table
A monthly resolved coral δ18O record from Sabine Bank, Vanuatu (SBV; 166.04° E, 15.94°S), extending from 2006 to 1929 CE, is used to assess the influence of sea surface salinity (SSS) on the oxygen isotopic composition of coral aragonite at this location. Monthly SSS anomalies at SBV between 2006 and 1970 are strongly correlated with monthly anomalies in sea surface temperature (SST) variations in the central Pacific cold tongue, as recorded by SST anomalies in the Niño 3.4 grid box (i.e., canonical record of ENSO variability, r = 0.68, p < 0.01; lag of 6 months). This relationship demonstrates that SSS in the waters offshore of Vanuatu respond to ENSO-driven changes in the coupled ocean-atmosphere system in the tropical Pacific. SBV coral δ18O is also strongly correlated with monthly instrumental SSS anomalies at Vanuatu (r = 0.71, p < 0.01), therefore SBV coral δ18O variations are driven by the ENSO-related changes in surface ocean conditions. A calibration-verification exercise using SBV coral δ18O values and instrumental SSS was performed over the period 2006-1970 CE. A statistically robust transfer function was determined and used to predict SSS at SBV back to 1929 CE. The coral δ18O and SSS relationship at Vanuatu is further evaluated via comparison with a coral δ18O record from Malo Channel, Vanuatu, a site that is 130 km to the east of SBV. The strong correlation between the two coral δ18O records (r = 0.70; p < 0.01) suggests that ENSO drives regional changes in SSS in this region and that such changes can be reconstructed using variations in skeletal δ18O of corals.
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THREE-DIMENSIONAL GAS MIGRATION AND GAS HYDRATE SYSTEMS OF SOUTH HYDRATE RIDGE, OFFSHORE OREGON
Emily Megan Graham, M.S. Geo. Sci.
University of Texas at Austin, May 2011
Supervisor: Nathan L. Bangs
87 pages, 47 references
Hydrate Ridge is a peanut shape bathymetric high located about 80 km west of Newport, Oregon on the Pacific continental margin, within the Cascadia subduction zone's accretionary wedge. The ridge's two topographic highs (S. and N. Hydrate Ridge) are characterized by gas vents and seeps that were observed with previous ODP initiatives. In 2008, we acquired a 3D seismic reflection data set using the P-Cable acquisition system to characterize the subsurface fluid migration pathways that feed the seafloor vent at S. Hydrate Ridge.
The new high-resolution data reveal a complex 3D structure of localized faulting within the gas hydrate stability zone (GHSZ). We interpret two groups of fault-related migration pathways. The first group is defined by regularly- and widely-spaced (100-150 m) faults that extend greater than 300ms TWT (~ 250 m) below seafloor and coincide with the regional thrust fault orientations of the Oregon margin. The deep extent of these faults makes them potential conduits for deeply sourced methane and may include thermogenic methane, which was found with shallow drilling during ODP Leg 204. As a fluid pathway these faults may complement the previously identified sand-rich, gas-filled stratigraphic horizon, Horizon A, which is a major gas migration pathway to the summit of S. Hydrate Ridge. The second group of faults is characterized by irregularly but closely spaced (~ 50 m), shallow fractures (extending < 160ms TWT below seafloor, ~ 115 m) found almost exclusively in the GHSZ directly beneath the seafloor vent at the summit of S. Hydrate Ridge. These faults form a closely-spaced network of fractures that provide multiple migration pathways for free gas entering the GHSZ to migrate vertically to the seafloor. We speculate that the faults are the product of hydraulic fracturing due to near-lithostatic gas pressures at the base of the GHSZ. These fractures may fill with hydrate and develop a lower permeability, which will lead to a buildup of gas pressures below the GHSZ. This may lead to a vertical propagation of new fractures to release the overpressure, which results in the high concentration of shallow fractures within the GHSZ seen in the 2008 data.
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GEOLOGIC FRAMEWORK OF THE SIERRA MOJADA MINING DISTRICT, COAHUILA, MEXICO: AN INTEGRATIVE STUDY OF A MESOZOIC PLATFORM-BASIN MARGIN
Sean Michael Gryger, M.S. Geo. Sci.
University of Texas at Austin, December 2010
Supervisor: J. Richard Kyle
376 pages, 152 references, 4 tables
The geology of the Sierra Mojada silver-lead-zinc mining district gives new insights into the stratigraphic evolution of the Coahuila Block and the Coahuila Folded Belt and the history of deformation along the basement-rooted San Marcos Fault Zone. Sierra Mojada provides the opportunity for substantial data collection relevant to the interaction of regional tectono-stratigraphic elements in a generally data-poor region of northeastern Mexico. Active mineral exploration has produced an extensive database of closely spaced drill core. Expansive underground workings facilitate subsurface geologic mapping. Sierra Mojada is situated at the northwestern edge of two tectono-stratigraphic provinces, the Coahuila Block, to the south, and the Coahuila Folded Belt, to the north. The San Marcos Fault, a west-northwest-trending regional structure extends through Sierra Mojada and is the informal boundary between these two provinces.
Sierra Mojada is situated on uplifted and deformed late Paleozoic Ouachita siliciclastic strata intruded by Triassic diorites. This basement is diagnostic of the Coahuila Block. Basement rocks are overlain by an immature conglomerate that is interpreted to be the updip equivalent of the Jurassic La Casita Formation. The stratigraphy of Sierra Mojada principally consists of a continuous succession of Barremian through Albian carbonates unconformably overlying the basal conglomerate. The Barremian-Aptian Cupido Formation locally records deepening conditions from a clastic-influenced evaporitic interior to high energy, open water conditions. The shale and lime mudstone of the La Pena Formation were deposited during a Gulf-wide transgression that signals the end of the Aptian. The Sierra Mojada region of the Coahuila Block was inundated throughout the Aptian and was affected by the late Aptian transgression. The Albian Aurora Formation constitutes the bulk of the Cretaceous section. Sierra Mojada exposes the Aurora shelf rim, progressing from platform margin to shelf rim and platform interior facies.
The structural features of Sierra Mojada affect the entire Cretaceous section. The high angle San Marcos Fault was reactivated with reverse motion during the Paleogene as a result of Laramide shortening. This juxtaposed basement and Jurassic conglomerate against the Cretaceous carbonates consistent with offset observed along the southern trace of the San Marcos Fault. A local colluvial unit suggests a lag in Laramide deformation. The carbonate strata and colluvial unit were overridden by a low angle, northeast-dipping thrust fault that placed a Neocomian through Aptian sequence atop the autochthonous Aptian-Albian carbonates. The allochthonous San Marcos Formation suggests regional-scale tectonic transport of this immature fluvial conglomerate from a downdip depozone within the Sabinas Basin. Kinematic indicators are consistent with the southwest-northeast axis for maximum compression established for Paleogene shortening throughout the Coahuila Folded Belt. The thrust fault bisects the principal ore zone within the Lower Aurora and upper La Pena Formations. This relation constrains the minimum age of ore emplacement to the Paleogene and suggests mineralization was genetically tied to the late stages of the Laramide Orogeny.
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QUANTIFICATION OF THE CONFIDENCE THAT CAN BE PLACED IN LAND-SURFACE MODEL PREDICTIONS: APPLICATIONS TO VEGETATION AND HYDROLOGIC PROCESSES
Lindsey Elizabeth Gulden, Ph.D.
University of Texas at Austin, August 2009
Supervisor: Zong-Liang Yang
156 pages, 138 references, 12 tables
The research presented here informs the confidence that can be placed in the simulations of land-surface models (LSMs).
After introducing a method for simplifying a complex, heterogeneous land-cover dataset for use in LSMs, I show that LSMs can realistically represent the spatial distribution of heterogeneous land-cover processes (e.g., biogenic emission of volatile organic compounds) in Texas. LSM-derived estimates of biogenic emissions are sensitive (varying up to a factor of 3) to land-cover data, which is not well constrained by observations. Simulated emissions are most sensitive to land-cover data in eastern and central Texas, where tropospheric ozone pollution is a concern. I further demonstrate that interannual variation in leaf mass is at least as important to variation in biogenic emissions as is interannual variation in shortwave radiation and temperature. Model estimates show that more-humid regions with less year-to-year variation in precipitation have lower year-to-year variation in biogenic emissions: as modeled mean emissions increase, their mean-normalized standard deviation decreases.
I evaluate three parameterizations of subsurface hydrology in LSMs (with (1) a shallow, 10-layer soil; (2) a deeper, many-layered soil; and (3) a lumped aquifer model) under increasing parameter uncertainty. When given their optimal parameter sets, all three versions perform equivalently well when simulating monthly change in terrestrial water storage. The most conceptually realistic model is least sensitive to errant parameter values. However, even when using the most conceptually realistic model, parameter interaction ensures that knowing ranges for individual parameters is insufficient to guarantee realistic simulation.
LSMs are often developed and evaluated at data-rich sites but are then applied in regions where data are sparse or unavailable. I present a framework for model evaluation that explicitly acknowledges perennial sources of uncertainty in LSM simulations (e.g., parameter uncertainty, meteorological forcing-data uncertainty, evaluation-data uncertainty) and that evaluates LSMs in a way that is consistent with models' typical application. The model performance score quantifies the likelihood that a representative ensemble of model performance will bracket observations with high skill and low spread. The robustness score quantifies the sensitivity of model performance to parameter error or data error. The fitness score ranks models' suitability for broad application.
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FACIES CHARACTERIZATION AND STRATIGRAPHIC ARCHITECTURE OF ORGANIC-RICH MUDROCKS, UPPER CRETACEOUS EAGLE FORD FORMATION, SOUTH TEXAS
Ryan Lee Harbor, MSGeoSci
University of Texas at Austin, August 2011
Co-Supervisors: Stephen C. Ruppel and William L. Fisher
184 pages, 102 references, 1 table
The Eagle Ford is a well-known source rock for both sandstone (Woodbine) and carbonate (Austin and Buda) hydrocarbon reservoirs in East and South Texas. Recent discoveries have demonstrated that source rocks, such as the Eagle Ford, are capable of producing significant volumes of gas and oil. At the same time, variations in well producibility indicate that these rocks, like conventional reservoirs, display considerable geological heterogeneity. Yet, only limited research has been published on the subsurface stratigraphy and character of Eagle Ford facies. Understanding the types, controls, and distribution of these heterogeneities requires in-depth rock-based studies.
In order to characterize Eagle Ford facies, 27 cores from 13 counties were investigated for rock textures, fabrics, sedimentary structures, and fossil assemblages. These studies were supported by light and electron microscopy as well as analysis of elemental chemistry and mineralogy. Regional subsurface stratigraphic correlations and facies distributions were defined using wireline logs calibrated from core studies.
In South Texas, the Eagle Ford Formation was deposited during a second-order transgressive/regressive cycle on the flooded, oxygen-restricted Comanche Shelf. Nine depositional facies consisting predominately of organic-rich, fine-grained (5.0 % TOC) to coarser-grained (3.05 % TOC) fabrics were identified. Facies developed in low-energy environments episodically interrupted by higher-energy, event sedimentation (current winnowing, cohesive and non-cohesive density flows, and turbidity flows). Locally, these rocks show evidence of early diagenetic recrystallization of calcite.
Concurrent water anoxia and organic matter preservation persisted locally into later Austin deposition, resulting in formation of a three-fold division of the Cenomanian-Coniacian Eagle Ford Formation. Common facies of lower and upper Eagle Ford members include (1) unlaminated, fissile, clay- and silica-rich, organic-rich mudrocks, (2) laminated, calcareous, organic-rich mudrocks, and (3) laminated, foraminifera- and peloid-rich, organic-rich packstones. The transitional Eagle Ford member consists of highly-cyclic (1) ripple-laminated, organic-rich wackestone (cycle base) and (2) burrowed, organic-lean lime wackestones (cycle top). Transitional Eagle Ford facies developed in oxygen-restricted, basinal depositional environments as distal equivalents to burrowed, foraminiferal lime wackestones of the Austin Formation.
Facies complexities in the Eagle Ford stem from complicated and interrelated processes of sediment production and distribution, diagenesis, and water column chemistry. Integrated core studies shed light on both controls of facies formation and their spatial distribution. These findings provide a framework for upscaling the fine-scale, heterogeneous character of shelfal Eagle Ford mudrocks; thus allowing development of predictive models into the distribution of key reservoir properties in the subsurface.
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FAULT-RELATED FRACTURE SYSTEMS IN THE CAMBRIAN ERIBOLL FORMATION, NORTHWEST SCOTLAND: A FIELD AND PETROGRAPHIC STUDY OF A TIGHT GAS SANDSTONE ANALOG
Peter Gregory Hargrove, M.S. Geo Sci
University of Texas at Austin, August 2009
Supervisor: Stephen E. Laubach
398 pages, 274 references, 9 tables
Lower Cambrian Eriboll Formation sandstones of the Ardvreck Group that crop out in the Hebridean foreland west of the Paleozoic Moine Thrust Zone (MTZ) in the Northwest Highlands of Scotland contain five sets of opening-mode fractures with varying degrees of quartz deposits (cement) and topographically prominent but small displacement (mostly less than 10 m) northeast-striking faults. The faults crosscut and in some places displace the MTZ. I interpret these faults to post-date the MTZ and consider them to be late structures (kinematically unrelated to MTZ emplacement). Sparse slip lineations on fault surfaces and offset patterns are evidence for strike-slip to oblique slip. Using geologic mapping I show that relative to their lateral and vertical extents, the faults display small amounts of offset (less than 5 to 10 m). My research documented the patterns and petrology of fractures in a well exposed section of the foreland, documented for the first time fracture patterns adjacent to and within the post-MTZ fault zones, and proposes an account of how fault and fracture patterns developed and their probable effects on fluid flow. Fractures are barren (joints), partially filled (quartz lined), or completely filled (veins). Older fracture sets are typically completely filled, whereas younger sets may be lined with a thin veneer of quartz cement or are barren. Listed in order from oldest to youngest fractures containing quartz strike north, NW to WNW, NE, west, and north (sets A through E respectively). Previously proposed relative ages of the sets were confirmed using crosscutting relationships and preferred orientations of macro- and microfractures (Laubach and Diaz-Tushman, 2009).
This study focuses on late northeast-striking fractures (set C) which I interpret to be related to the formation of the small-offset faults. Many of the attributes of late fractures and faults in the Eriboll Formation resemble those found in core from highly quartz cemented sandstone natural gas reservoirs ("tight gas sandstones"). I demonstrate that the well exposed fracture patterns I documented are good analogs for tight gas sandstones, by investigating fracture characteristics such as network configurations and connectivity, fracture intensity (abundance), fracture scaling, fracture length and spacing, and the degree of quartz cement deposits in fractures and cataclastic fault rock. Many of the narrow macroscopic fractures and microfractures I documented using CL methods contain varying amounts of quartz deposits. The excellent preservation of Eriboll outcrops is probably a manifestation of little or no fracture pore space preservation in many of the numerous fractures that are apparent in outcrop. Set C fracture abundance is not distributed in a uniform envelope (or "halo") around the late faults. Using scanlines, I show that set C fracture distribution is heterogeneous and highly variable over short lateral distances (tens of centimeters to meters).
I also investigate wing crack assemblages (secondary opening-mode fractures) that are locally associated with set C fractures. The assemblages accommodate small amounts of the distributed displacement (a few millimeters) adjacent to fault zones and are locally responsible for increased amounts of fracture connectivity by linking neighboring fractures. Variations in fracture pattern complexity appears to be related to the presence (or absence) of wing crack assemblages. Localized wing crack development on closely spaced, en echelon set C fractures also leads to precursory development of fragmented lozenges of highly deformed volumes of rock (damage zones) that resemble geometries similar to those seen in preserved Eriboll fault cores.
Fault-related deformation in the Eriboll Formation is markedly different than that in the underlying Late Proterozoic Torridonian Applecross Formation (subarkose fluvial sandstone), which is characterized by simple halos fault-related fracture arrays surrounding the same late (post-MTZ) faults. In addition to composition, the Eriboll and Applecross differ in mechanical layer thickness (centimeters versus > tens of meters), mechanical properties (high versus low brittleness), and greater propensity for fractures to be filled with quartz cement in Eriboll sandstones owing to quartz cement growth being impaired by the abundance of non-quartz substrate (feldspar and clay minerals) along fracture walls in the Applecross Formation. Although the Eriboll sandstones are more highly fractured than the older Applecross sandstones, Eriboll fractures are more prone to be filled by quartz cement.
In this thesis I also report previously unrecognized early (set A; pre-MTZ) minor normal faults, sandstone petrography and rock mechanical properties of selected Eriboll sandstone samples, and the influence of fractures on the glacial geomorphology of the area. I also describe a previously unmapped igneous dyke. I describe previously unrecognized vugs that are partly strata bound and partly localized along fractures. The attributes of these vugs and a review of the literature suggests that these features could represent evidence of pre-glacial silici-karst in Eriboll quartzites.
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QUANTIFIED FACIES DISTRIBUTION AND SEQUENCE GEOMETRY OF THE YATES FORMATION, SLAUGHTER CANYON, NEW MEXICO
Charles Averill Harman, M.S.Geo.Sci.
University of Texas at Austin, August 2011
Supervisor: Charles Kerans
137 pages, 104 references, 4 tables
This study uses a new integrated outcrop data and airborne lidar from Slaughter Canyon, New Mexico, to quantitatively characterize the cycle-scale facies architecture within the G23-G26 high frequency sequences of the Yates Formation. High frequency cycle-scale mapping of these sequences shows sedimentological evidence for accommodation reduction associated with the Permain composite sequence (CS) 13 highstand (G23-G25). Development of the G26 HFS additionally demonstrates the isochronous balance of mixed carbonate-siliciclastic deposition across the Yates-Capitan reef-rimmed shelf during the initial CS-scale transgression following significant exposure and bypass of sand across the shelf.
This sequence framework is quantitatively analyzed using progradation to aggradation (P/A) ratios, facies proportions, facies tract dip width, and facies tract bedding angles to evaluate the interplay of eustacy and syndepositional deformation as drivers of stratigraphic architecture. The sequences defined here developed in response to both eustacy and syndepositional deformation, but individual facies distributions and cycle stacking patterns were largely controlled by eustacy; while facies, cycle, and sequence thicknesses as well as facies bedding angles were locally influenced by syndepositional faulting. A reconstruction of each high frequency sequence and stepwise documentation of post-depositional fault displacement and HFS basinward rotation was generated using the lidar data. This analysis shows that the G23-G26 HFS developed basinward-dipping depositional topography from the shelf crest to the shelf margin reef. This geometry was largely unaltered by syndepositional faults during individual HFS deposition, but was rotated basinward shortly thereafter by younger fault movement.
The accommodation trends recorded in this largely shelf crest to shelf margin window can be additionally projected into the middle shelf producing zones of the prolific Yates-aged reservoirs on the Northwest Shelf and Central Basin Platform.
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ASSESSING THE KINEMATIC SIGNIFICANCE OF THE PLATTENGNEIS, A MAJOR INTRACRUSTAL TRANSPORT HORIZON IN THE KORALPE REGION, EASTERN ALPS
Elizabeth Rose Hatley, M.S. Geo. Sci.
University of Texas at Austin, August 2010
Supervisor: William D. Carlson
270 pages, 30 references, 1 table
The Plattengneis shear zone is a major Eo-Alpine intracrustal transport horizon that extends over ~ 1000 km2 of the Koralpe region in the Eastern Alps of Austria. Because several prior studies of the shear zone and its surroundings have produced conflicting interpretations, the kinematic significance of the Plattengneis to the regional tectonometamorphic evolution of the Koralpe region and the Eastern Alps remains controversial. In this study, quartz lattice preferred orientations were interpreted in relation to the vertical position of the samples within the shear zone, to expand upon previous data focused on their lateral (north-south) locations. Vertical positions were determined using a 3D model of the Plattengneis, and this information was combined with the lattice preferred orientation of quartz in each sample, measured using electron backscatter diffraction. This approach provides information on the vertical distribution within the shear zone of dynamic recrystallization processes, activated slip systems, temperatures, shear senses, and strain geometry. The dominance of dynamic recrystallization by grain boundary migration, together with the activation primarily of prism ‹a› slip systems, with subsidiary activation of rhomb ‹a› and basal ‹a› slip systems, are indicators of high-temperature deformation that are interpreted to be within the range of ~ 500° C to 700° C for all samples in this study. Both top-to-the-north and top-to-the-south shear senses are seen in the quartz fabrics, and none of the features observed in the quartz lattice preferred orientations shows any systematic variation with vertical position in the shear zone. Strain throughout the shear zone is characterized by dominant simple shear with a component of constriction; no evidence of flattening was observed. The results from this study are consistent with interpretations in which the Plattengneis formed during nappe emplacement, through thrust-related kinematics. This study found no evidence to support interpretations in which the Plattengneis formed during exhumation of the Koralpe region.
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GROUNDWATER FLOW AND RECHARGE WITHIN THE BARTON SPRINGS SEGMENT OF THE EDWARDS AQUIFER, SOUTHERN TRAVIS AND NORTHERN HAYS COUNTIES, TEXAS
Nico Mark Hauwert, Ph.D.
University of Texas at Austin, May 2009
Supervisor: John M. Sharp, Jr.
328 pages, 442 references, 9 tables
The Barton Springs Segment, part of the karstic Edwards aquifer in Central Texas, is a Sole Source aquifer, is habitat to rare karst species, and provides water to a well-loved municipal swimming pool, yet its hydrogeologic properties remain insufficiently understood. For this study, the hydrogeologic characteristics of the Barton Springs Segment were investigated using several approaches, including mapping of hydrostratigraphic units and faults, measurement of upland infiltration, groundwater traces, and aquifer tests. The depositional environment, diagenesis, fracturing, down-dropped and dipping faulted blocks, and subsequent dissolution were determined to play important roles in controlling groundwater flow-path development within the Barton Springs Segment. In particular, downdropped fault blocks create groundwater gradients to the southeast that influence flow in the Edwards outcrop area. Upland internal drainage basins were found to be extremely efficient at conveying recharge to the underlying aquifer. The maturity of natural internal drainage sinkholes can be measured by its bowl volume, which grows in proportion to the catchment area it captures. A 19-hectare internal drainage basin, HQ Flat sinkhole, was monitored for rainfall, evapotranspiration, soil moisture, and discrete runoff to the cave drain. During a 505-day period, 5.5% of measured rainfall entered the cave drain as discrete recharge, 26% of measured rainfall infiltrated through soils on the slopes, and the remaining 68% was lost through evapotranspiration. This amount of upland infiltration is consistent with infiltration measurements in other karst areas and is much larger than the 1% upland recharge of rainfall that was previously estimated. A chloride mass balance indicates that at the adjacent Tabor research site, about 50% of rainfall infiltrates to a 6-meter depth. Dye-tracing and pump tests demonstrated that primary and secondary groundwater flow paths are the major influence on transmissivity within the Barton Springs Segment. Groundwater tracing breakthroughs reveal very high advection and relatively low dispersion. Drawdown response to pump tests indicates a very high degree of anisotropy, controlled by location of groundwater flow paths. Overall the Barton Springs Segment is a mature karst aquifer with highly developed rapid, discrete network for both recharge and groundwater-flow.
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ENERGY-WATER NEXUS: SUSTAINABILITY OF COAL AND WATER RESOURCES
Anna Kathleen Hebel, M.A.
University of Texas at Austin, May 2010
Supervisor: Charles Groat
70 pages, 42 references, 3 tables
Energy and water are two precious natural resources with which demand will continue to grow with increased population growth. Coal provides a cheap and abundant source of energy but with important environmental effects on air and water. An analysis of the current coal production in Texas, one of the leading providers of energy in the United States, will be discussed along with the possibility of creating a coal-to-liquids market in Texas from existing and future coal mining operations. An in-depth discussion into the water requirements for traditional coal production and coal-to-liquids will assist in analyzing its possible production and sustainability.
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RESERVOIR CHARACTERIZATION AND SEQUENCE STRATIGRAPHY OF PERMIAN SAN ANDRES PLATFORM CARBONATES, FULLERTON FIELD, PERMIAN BASIN, WEST TEXAS
Dana Kristin Helbert, MSGeosci
University of Texas at Austin, May 2010
Co-Supervisors: Stephen C. Ruppel and Charles Kerans
164 pages, 95 references
The San Andres Formation (Permian, Guadalupian) is the most prolific oil reservoir in the Permian basin. However, despite more than 60 years of production, an estimated 70% of the original oil in place remains. Recovery of this huge resource requires a better understanding of facies and reservoir framework, which, in turn, must be accomplished using a rock-based reservoir characterization process. This high resolution correlation method is essential for understanding the complex heterogeneities found in shallow water platform carbonates.
Steps in the construction of a rock-based reservoir model in the Fullerton San Andres Unit (FSAU) included (1) defining depositional facies and primary facies groups; (2) creating an outcrop depositional model; (3) integrating facies descriptions with gamma-ray and porosity log data; (3) defining field-wide high frequency sequences based on wireline logs and cycle stacking patterns; (4) developing a sequence-based reservoir framework and 3-dimensional reservoir architecture; (5) defining porosity and permeability relationships for facies groups based on rock fabric characteristics.
In Fullerton Field, the San Andres Formation comprises high frequency cycles of upward shoaling shallow-marine carbonates. Studies of nine cores (1730 ft) in FSAU reveal four peritidal and five shallow subtidal depositional facies based on texture, fossil assemblages, and sedimentary structures. Peritidal facies are dominantly laminated carbonate mudstones, interpreted as deposited on an intermittently exposed tidal flat. Shallow subtidal facies are peloid and mollusk dominated wackestones and packstones, interpreted as deposited in a shallow protected lagoon. Cycle stacking patterns indicate four complete upward shallowing high frequency sequences. Comparison of high frequency sequences between cored wells shows a high degree of similarity in the overall generalized vertical sequence, especially in the proportions of peritidal and subtidal components within each sequence. Three-dimensional reservoir characterization, using 132 gamma ray and porosity logs, reveals that depositional sequences are largely flat-lying with local topographic variation identified as the fundamental influence on lateral facies distribution within the reservoir section.
Integration of core and petrophysical data from surrounding fields places FSAU in the larger sequence stratigraphic framework of the Central Basin Platform. The regional depositional sequence formed a series of depositional environments ranging from intermittently exposed to open marine. San Andres facies developed during south-easterly progradation of shallow water tidal flat and sabkha sediments over a deeper open marine shelf.
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STRATIGRAPHIC HIERARCHY AND SHELF-TO-BASIN ARCHITECTURE OF APTIAN-ALBIAN MURAL SHELF, CERRO CALOSO RANGE, SONORA, MEXICO
Samuel Franz Hiebert, BAUniversity of Texas at Austin, December 2010
Supervisors: Charles Kerans
61 pages, 19 references
Detailed outcrop studies represent one of the best techniques for improving our ability to characterize reef-rimmed carbonate shelves in the subsurface. This study furthers our knowledge of Cretaceous greenhouse platform margins using an exceptional continuous shelf-to-basin profile from northern Sonora, Mexico. The nature of the shelf-to-basin transition is examined by comparing four parameters across three third-order sequences; reef framestone lateral and vertical dimensions, fore-reef slope lateral and vertical dimensions, evolution of platform interior facies, and presence or absence of lowstand systems tract clastic wedges.
The unit of interest is the Lower Albian Mural Limestone that extends from southeastern Arizona into northeastern Mexico. The Mural-Caloso shelf is one of the least studied continuously exposed shelf-to-basin carbonate platform transects in the world, having been most recently examined by Warzeski (1983). The principle research objective of this study was to establish a modern sequence Stratigraphic framework by outlining the facies transitions and stratal geometries associated with third order-sequences proximal to the platform margin for the upper portion of the Lower Albian age Mural- Caloso shelf system. The southernmost or "C" section of the Cerro Caloso was selected for detailed study because optimum shelf-edge reef development and presence of onlapping siliciclastic wedges allowed delineation of major sequence boundaries.
Three vertical sections were measured and tied to aerial photopans in order to link stratal geometries observed from photopans and in the field with small-scale facies variability. Ten facies were identified, that describe depositional environments ranging from low-energy platform interior, through reef core, fore-reef, and deeper-water shelf/basin. These facies and associated stacking patterns and stratal geometries led to the recognition of three 3rd order depositional sequences within the upper portion of the Lower Albian (Glen Rose-equivalent 106-112 Ma) 2nd order supersequence. During deposition of these three sequences the Mural-Caloso Shelf evolved from a carbonate shelf system with a well-defined coral-rudist margin and broad platform interior factory, to one with a siliciclastic-dominated platform interior and narrow carbonate rim. Facies tract dimensions were collected for the fore-reef slope, reef core, and back-reef apron. These dimensions and their link to progradation/aggradation patterns will aid in the prediction of subsurface-reservoir facies development.
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ASSESSING THE IMPACT OF COMMODITY PRICE ASSUMPTIONS ON FACILITY OPTIMIZATION: A CASE IN OFFSHORE OIL AND GAS
Enes Hosgor, M.A.
University of Texas at Austin, May 2009
Supervisor: Christopher J. Jablonowski
78 pages, 55 references
Commodity price assumptions certainly influence individual project economics, and may affect the ranking and selection of projects within a portfolio. But price assumptions can have other impacts. For example, price assumptions may influence the choice of capacity for the facility during the planning phase. The purpose of this thesis is to specify and demonstrate a systematic workflow for assessing the impact of price assumptions on facility optimization. The study has three main objectives: To investigate how different commodity price assumptions affect (1) facility optimization in the planning phase, (2) the value of the option to expand the facility capacity at a future date, and (3) the value of information (VOI) on important valuation and planning inputs (e.g. reserves).
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GEOCHEMISTRY AND GEOCHRONOLOGY OF META-IGNEOUS ROCKS FROM THE TOKAT MASSIF, NORTH-CENTRAL TURKEY
Kathryn Huber, M.S. Geological Sciences
University of Texas at Austin, December 2011
Supervisor: Elizabeth Catlos
136 pages, 117 references, 6 tables
Located in the Sakarya Zone of the eastern Pontides, the Tokat Massif is a Permian-Triassic metamorphic, volcanic, and sedimentary group of rocks cut by strands of the active strike-slip North Anatolian Shear Zone (NASZ). The assembly of the Tokat Massif is debated and is likely due to the region's complex tectonic history. According to one interpretation, the massif is comprised of various imbricated piles of Pre-Tethyside and Tethyside units fragmented by the NASZ. Others distinguish three specific units that make up the subduction-accretion complex: the Tokat, Yesilirmak, and Akdagmadeni Groups. The Tokat Group is a pre-Jurassic metamorphic unit made up of a heterogeneous mélange and associated metasedimentary rocks. It has also been proposed that the Tokat Group is the easternmost extension of the Karakaya Complex, an extensive Permian-Triassic metamorphic unit within the Sakarya zone. The history of the Karakaya Complex is disputed and either represents oceanic rift deposits which developed into a marginal ocean basin or accretion-subduction units of the Paleo-Tethys. Structurally incorporated into the Tokat Massif is a Cretaceous ophiolitic mélange that formed from the closing of the Neo-Tethyan ocean basin, and it is proposed that the closing of the Paleo- and Neo-Tethys are both documented by imbricated thrust faults in the region. Metagabbros, metabasites, and serpentinites (n=38, 9 sample locations) were collected from the Tokat Group and metabasalts (n=8) were collected from a Cretaceous ophiolitic mélange. These rocks were studied to determine geologic source and age. All rocks from the Karakaya Complex are both oceanic rift-related and enriched from a deeper OIB plume source based on REE, trace element and clinopyroxene mineral chemistry. Metabasalts from the Cretaceous mélange have IAT affinites based on REE patterns and trace geochemical data. Karakaya gabbroic rocks were likely generated by mixing of plume-related and enriched magmas near the rifting Paleotethyan ocean crust. Metamorphism and deformation occurred during the northward subduction of the Paleotethyan ocean basin and accretion of the Karakaya units to the Laurasian continental margin. Small (‹20 μm) zircon and baddeleyite grains from four Karakaya samples were dated in thin section using a Cameca 1270 ion microprobe at UCLA. The rocks yield a maximum 238U/206Pb crystallization age of 256±17 Ma (±1σ) and minimum metamorphic age of 173±9 Ma.
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STRATIGRAPHIC ARCHITECTURE, DEPOSITIONAL SYSTEMS, AND RESERVOIR CHARACTERISTICS OF THE PEARSALL SHALE-GAS SYSTEM, LOWER CRETACEOUS, SOUTH TEXAS
David Christopher Hull, MSGeoSci
University of Texas at Austin, August 2011
Co-Supervisors: Robert G. Loucks and Kitty Milliken
192 pages, 165 references, 2 tables
This study examines the regional stratigraphic architecture, depositional systems, and petrographic characteristics of the South Texas Pearsall shale-gas system currently developed in the Indio Tanks (Pearsall) and Pena Creek (Pearsall) fields. The Pearsall Formation was deposited as a mixed carbonate-siliciclastic system on a distally steepened ramp over a period of 11.75 million years. It was deposited between maximum floods of two second-order sequences and contains at least five third-order cycles. Up to three Oceanic Anoxic Events (OAE 1-A, Late Aptian Regional Event, and OAE 1-B) figure prominently in the deposition of the Pearsall sediments, and during these intervals, depending on the location within the Maverick Basin, sedimentation rates were between 0.5 and 2 cm/ky. Facies in the Pearsall section arise from interactions between pre-existing topography, oxygenation regime, eustatic sea-level fluctuation, and depositional processes.
In the Pearsall Formation, OAEs affected depositional environments and resulting facies patterns during several time periods. The OAEs occurred in association with transgressions but not necessarily in concert with them. Outer ramp OAE facies are siliciclastic-dominated, TOC-rich, and little-bioturbated. Conversely the outer ramp facies deposited under normally oxygenated paleoenvironmental conditions tend to be carbonate-rich, TOC-poor, and are more prominently bioturbated.
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STRUCTURAL MODEL AND FRACTURE ANALYSES FOR A MAJOR GAS EMPLACEMENT IN DEVONIAN SANDSTONES OF THE SUBANDES
Juan Francisco Pedro Iñigo, MS in Geological Sciences
University of Texas at Austin, August 2009
Supervisor: Stephen E. Laubach
297 pages, 167 references, 15 tables
The fold and thrust belt of the Subandean Ranges (central and southern Bolivia, and northern Argentina) contains both gas and condensate production and reserves in Devonian quartzose sandstones within deep structures. Reservoir sandstones present values of permeability close to 0.01 mD, implying that reservoir drainage must be controlled by a fracture system that enhances permeability. Hydrocarbon production in naturally fractured reservoirs is affected by fracture quality (degree of openness), spatial arrangement, size distribution (including aperture, height and length), fracture abundance, and arrangement with respect to stratigraphic and macro-structural features. Systematic study of fractures in the subsurface is complicated by the small probability that a well will intersect sufficient fractures for direct analysis of their attributes. Because of this fracture data obtained from logging and coring must be complemented with alternative methodologies. In my study I performed a workflow that includes geologic mapping of outcrop analogs of subsurface units, fracture characterization in outcrops and thin sections, the construction of kinematic structural model using algorithms for 3D analysis, petrographic description of composition and diagenesis, and statistical multivariate analyses in order to define how structural, lithologic and diagenetic features affect fracture distribution.
From the construction of a structural model and the analyses of its properties, I generated semi-quantitative models of fracture attributes based on classic fold-related fracture concepts. This model was tested with direct fracture observations from core and outcrop, coupled with microstructural imaging using SEM-CL, to document fracture attributes. The models all show high curvature and strain values homogeneously distributed along the azimuth and close to the hinge of the anticline, which implies this domain should be most fractured. On the other hand, microfracture studies reveal that although highest strain values are found in the hinge, low strains also are found along the hinge even for samples with similar lithologies.
The study of macro and microfractures in outcrop and core samples allowed me to clearly identify two opening mode fracture sets for the Devonian sandstones. These present an orthogonal arrangement and variable cross cutting relations. The dominant set (defined as Set I) has a WNW strike and is perpendicular to the structural trend of the Subandean Ranges; the subordinate set (defines as Set II) has a NNE strike, and is parallel to the previously mentioned structural trend. Set I has higher strain accumulation, log-normal spacing distribution, and is strongly controlled by the primary quartz content of the rocks. Set II also has a log-normal spacing distribution, and presents structural control.
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REMOTE SENSING, GEOCHEMISTRY, GEOCHRONOLOGY, AND CATHODOLUMINESCENCE IMAGING OF THE EGRIGOZ, KOYUNOBA, AND ALACAM PLUTONS, NORTHERN MENDERES MASSIF, TURKEY
Lauren Rolston Jacob, M.S. Geo. Sci.
University of Texas at Austin, May 2011
Supervisor: Elizabeth Catlos
131 pages, 148 references, 13 tables
The Egrigoz, Koyunoba, and Alacam plutons are located in the Northern Menderes Massif of western Turkey between the Simav normal fault to the south and the Izmir-Ankara-Erzincan suture to the north. Although much attention has focused on their geochemical and geochronological history, their relationship to each other and other major structures in the region is still debated. Some geologic maps show the Egrigoz and Koyunoba pluton bounded to the west by the low-angle Simav detachment fault. In contrast, other regional maps show no offsets between the plutons and surrounding metamorphic rocks. Yet other studies indicate thrust faults may be present near the Egrigoz pluton, between Menderes metamorphic rocks and a meta-rhyolite unit. To gain a better understanding of the history of the Egrigoz, Koyunoba, and Alacam plutons, ArcGIS digital elevation data from the region, geochronological data, geochemical analyses, and cathodoluminescence (CL) images were acquired to search for effects of micro- to macro-scales of deformation.
Numerous ~E-W trending extension lineations that parallel the Simav graben and cut the plutons were observed in relief images. These lineations, likely due to large-scale ~N-S extension, continue across plutons inferring that extension continued after the exhumation of these rocks. The Simav graben and its associated high-angle fault are evident in the elevation data, but no other significant detachment-related basins or structures are shown, including the low-angle Simav detachment.
U-Pb zircon ages, ranging from 29.9±3.9 Ma to 14.6±2.6 Ma, suggest the plutons crystallized over a ~15 m.y. time frame. Samples from the plutons are peraluminous S-type granite to granodiorites. The plutons were emplaced in a post-collisional volcanic-arc setting and range from magnesian to ferroan with increasing silica contents. Geochemical analyses show little difference between the three plutons, consistent with the rocks arising from a similar source.
To document microstructures that might help explain these heterogeneities, CL images were obtained. CL images document a complicated tectonic history including magma mixing, multiple episodes of brittle deformation, and fluid alteration. The CL images constitute evidence of a complex multi-stage tectonic history for the region that includes water-mediated brittle deformation.
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NEOGENE INTRUSIONS IN THE WESTERN CENTRAL RANGE, PAPUA, INDONESIA: PETROLOGIC, GEOCHEMICAL, AND ISOTOPIC COMPARISON OF THE MIOCENE ULAR MERAH AND PLIOCENE KOMOPA MAGMATIC DISTRICTS
Julia Elizabeth Jackson, M.S. Geo. Sci.
University of Texas at Austin, May 2010
Supervisor: Mark Cloos
360 pages, 78 references, 12 tables
New Guinea is a type locality for arc-continent collision. Two belts of Neogene igneous rocks parallel the spine of the Central Range fold-and-thrust belt for ~1000 km along the length of the island. Miocene (20 to 10 Ma) magmatic rocks crop out to the north of Pliocene (7 to 3 Ma) magmatic rocks. Miocene magmatic rocks in Papua New Guinea, the Maramuni Volcanic Arc, intruded Australian continental rocks whereas those in Papua, Indonesia, intruded allochthonous arc/forearc terranes. Pliocene magmatic rocks, which young from west to east, were emplaced into Australian continental crust at the highest elevations in the Central Range.
The Maramuni Volcanic Arc of eastern New Guinea has been attributed to southward-dipping subduction along the Trobriand Trough, but the origin of Miocene magmatic rocks in the western Central Range remains unclear. The origin of Plio-Pleistocene intrusions along the spine of the Central Range has been attributed to collisional delamination during mid-Miocene to Pliocene arc-continent collisional tectonism.
This study provides the first extensive petrographic, whole-rock geochemical, and isotopic analyses for two magmatic districts in the western Central Range: Komopa and Ular Merah. A total of 175 samples was collected from 28 Komopa drill cores, and 172 samples were collected from three Ular Merah drill cores. Of these samples, 169 samples were studied petrographically. A suite of 35 samples was selected for whole-rock geochemistry, of which 26 were also selected for Sr, Nd, and Pb isotopic analyses to constrain the magma source and crustal influence.
Komopa intrusions were emplaced at 3.9 to 2.9 Ma into Australian passive margin strata. These intrusions are hypabyssal quartz monzodiorites, granodiorites, and monzogranites with phenocrysts of pl + bt ± cpx ± hbl in a kfs + qtz + pl rich groundmass. Komopa intrusions are shoshonitic with high LREE and LILE and low Nb, Ta, and Ti concentrations. Moderately radiogenic 87Sr/86Sr (≈ 0.7077) and unradiogenic εNd (average ≈ -8.3) indicate the parent magma had a lithospheric mantle component. This study finds that Komopa intrusions are similar to intrusions from the Minjauh Volcanic Field, Ertsberg Mining District, and Etna Bay. These magmas are products of collisional delamination tectonism which began in the latest Miocene as the leading edge of the Australian continental lithosphere jammed the north-dipping subduction zone beneath the Irian Ophiolite.
Ular Merah intrusions, 17.4 to 16.6 Ma, were emplaced into the allochthonous Irian Ophiolite Belt. These intrusions are typically high-K calc-alkaline, porphyritic diorites and monzodiorites with phenocrysts of pl + bt ± cpx ± hbl ± kfs. The magmatic district is characterized by high Na2O, Sr, Cr, Ni, and low Y and Yb concentrations. Low 87Sr/86Sr (≈ 0.704), and radiogenic εNd (≈ 3.9) indicate a significant asthenospheric mantle component to the melt. These adakite-like geochemical characteristics lead to the conclusion that Ular Merah intrusions are the result of partially remelting garnet-bearing plutons emplaced into the mantle beneath the allochthonous ophiolite. Deep-seated plutons, results of Oligocene subduction magmatism at the Outer Melanesian Trench, were partially remelted during the initiation of rifting at the Ayu Trough during the mid-Miocene.
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REGIONAL-SCALE LAND–CLIMATE INTERACTIONS AND THEIR IMPACTS ON AIR QUALITY IN A CHANGING CLIMATE
Xiaoyan Jiang, Ph.D.
University of Texas at Austin, December 2010
Supervisor: Zong-Liang Yang
184 pages, 242 references, 9 tables
Land surface areas, which represent approximately 30% of the Earth's surface, contribute largely to the complexity of the climate system by exchanging water, energy, momentum, and chemical materials with the overlying atmosphere. Because of the highly heterogeneous nature of the land surface and its rapid transformation due to human activities, future climate projections are less certain on regional scales than for the globe as a whole. The work presented in this dissertation is focused on a better understanding of regional-scale land–atmosphere interactions and their impacts on climate and air quality. Specifically, I concentrate my research on three typical regions in the United States (U.S.): 1) the Central U.S. (representing transition zones between arid and wet climates); 2) the Houston metropolitan region (representing a major urban area); and 3) the eastern U.S. (representing temperate forested regions). These regions are also chosen owing to the consideration of data availability.
The first study concerns the roles of vegetation phenology and groundwater dynamics in regulating evapotranspiration and precipitation over the transition zones in summer months. It is found that the warm-season precipitation in the Central U.S. is sensitive to latent heat fluxes controlled by vegetation dynamics. Groundwater enhances the persistence of soil moisture memory from rainy periods to dry periods by transferring water to upper soil layers through capillary forces. Enhancement in soil moisture facilitates vegetation persistence in dry periods, producing more evaporation to the atmosphere and resulting in enhanced precipitation, which then increases soil moisture. The second study compares the impacts of future urbanization and climate change on regional air quality. The results show that the effect of land use change on surface ozone (O3) is comparable to that of climate change, but the details differ across the domain. The third study deals with the formation and distributions of secondary organic aerosols (SOA) — a largely overlooked but potentially important component in the climate system. Under future different climate scenarios, I found that biogenic emissions — an important precursor of SOA — are expected to increase everywhere over the U.S., with the largest increase found in the southeastern U.S. and the northwestern U.S., while changes in SOA do not necessarily follow those in biogenic emissions. Other factors such as partitioning coefficients, atmospheric oxidative capability, primary organic carbon, and anthropogenic emissions also play a role in SOA formation. Direct and indirect impacts from climate change complicate the future SOA formation.
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MICROBE-MINERAL AFFINITY IN SULFURIC ACID KARST SYSTEMS
Aaron Alexander Jones, MSGeoSci
University of Texas at Austin, August 2011
Supervisor: Philip Bennett
91 pages, 59 references, 14 tables
Microbial communities influence the kinetics and pathways of reactions involved in the dissolution of a number of minerals (Ehrlich 1996). On a smaller scale these interactions can affect substrate permeability, porosity, and create highly localized biogeochemical conditions. However, a mechanistic understanding of the consequences of microbial surface colonization on calcite dissolution rate has yet to be achieved. More specifically, little is known about the impact of sulfur-oxidizing bacteria activity on the rate of carbonate mineral dissolution, or the nature of the microbe-limestone attachment and interaction. Through a series of laboratory and field experiments the effect of mineral surface colonization by microbial communities, obtained from an active sulfuric acid cave (Lower Kane Cave (LKC), Big Horn Basin, WY), on the dissolution rate of Madison Limestone was quantified. Results from laboratory experiments showed that a microbial biofilm, composed primarily of Epsilonproteobacteria and Gammaproteobacteria growing on a limestone surface oxidized thiosulfate and increased carbonate dissolution rates up to 3.3 times faster than abiotic rates. When all thiosulfate substrate was withheld the community oxidized stored intracellular sulfur, continuing to accelerate limestone dissolution and decreasing pH. This process is sensitive to O2 limitations.
Characterization of this aggressive sub-biofilm corrosion was more closely examined by SEM imaging. By comparing mineral surface morphology of colonized chips to non-colonized chips of various carbonate substrates, it was shown that even under conditions near equilibrium with calcite, aggressive dissolution of carbonate substratum occurs exclusively beneath the biofilm. These findings support the hypothesis that (1) sulfur-oxidizing microbial communities aggressively dissolve carbonates in order to buffer the production of excess acidity by neutrophilic communities and (2) biofilm presence affects carbonate mineral dissolution by physically separating a bulk stream water from the sub-biomat environment.
Furthermore, it was found that mineralogy affects the degree of establishment of microbial communities in this environment. Results from a series of four laboratory and one in situ reactor experiment showed that limestone and dolostone substratum consistently had higher biomass accumulations than silicate minerals or pure Iceland spar calcite in the same reactor. These results provide evidence to support the hypothesis that mineralogy influences microbial accumulation in sulfuric-acid karst systems. Particularly, neutrophilic sulfur-oxidizing communities accumulate in greater quantities on solid substrates that buffer metabolically-generated acidity. These results also demonstrated the dependence of microorganisms on colonization of a particular mineral surface, possibly in order to gain access to micronutrients bound within solid substrates when exposed to nutrient-limited conditions.
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MODELING ADOPTION OF SOLAR PHOTOVOLTAICS AND ANALYSIS OF NET METERING IN THE CITY OF AUSTIN
Siva Kiran Josyula, MA
University of Texas at Austin, August 2011
Supervisor: Varun Rai
73 pages, 37 references, 17 tables
Solar photovoltaics have received government support in the form of rebates, tax credits and net metering tariff mechanisms. The intended goal of these incentives is to encourage innovation in the manufacturing and installation of these systems, which is expected to eventually help overcome the high cost barrier for the adoption of the technology. These systems have the advantages of abundant availability of the solar resource, low environmental footprint, and the possibility of onsite installation, reducing the need for additional generation and transmission capacity. Since millions of dollars have been invested in these incentive programs, there is an interest in tracking the progress in the cost and capacity installed.
In the first part of this thesis, I analyzed the trends in costs and adoption of solar PV by residential and commercial customers in the city of Austin. This is accomplished by tabular and graphical analysis of data on PV installations from 2004, when Austin Energy's rebate program started, to early 2010.
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THE EFFECTS OF PRESSURE VARIATIONS AND CHEMICAL REACTIONS ON THE ELASTICITY OF THE LOWER TUSCALOOSA SANDSTONE OF THE CRANFIELD FIELD, MISSISSIPPI
Xiaoyan Jiang, Ph.D.
University of Texas at Austin, August 2011
Supervisor: Corey Anthony Joy, MSGeoSci
97 pages, 31 references, 3 tables
Compliance with current and evolving federal and commercial regulations require the monitoring of injected carbon dioxide for geological sequestration. The goal of this project is to provide geophysicists with tools to quantitatively interpret seismic data for the amount of carbon dioxide retained in subsurface reservoirs. Rock physics can be used to predict the effects on the seismic response of injecting carbon dioxide on the reservoir. However, classical rock physics models fail when chemical reactions alter the microstructure of the host rock. These chemically induced changes can stiffen or soften the rock frame by precipitation or dissolution, respectively, of minerals in the pore space. Increasing pore pressure is another effect of sequestering carbon dioxide. The amount of change in the microstructure due to chemical reactions and pressure variations depends on the reservoir into which the fluid is injected. Therefore, measuring velocities on site-specific subsurface core samples may provide the ability to differentiate between chemical reactions and pressure variations on the elastic properties of the reservoir rock.
Core samples come from the Lower Tuscaloosa Sandstone of the Cranfield study area in Mississippi. The experiments consisted of injecting core plugs with carbon dioxide rich brine and measuring compressional and shear velocities at different effective pressures. The elastic moduli of the rock frame are calculated from the measured elastic wave propagation velocities at specific injected pore volumes and effective pressures.
Injecting carbon dioxide rich brine into sandstone core samples, which are composed on average of 80% quartz and 20% clay minerals, resulted in softening of the rock frame due to the dissolution of iron bearing minerals. The moduli exponentially decreased with injected pore volumes and were linearly proportional to effective pressure. The bulk modulus and rigidity of the more quartz rich sample decreased by 13% and 6.5%, respectively, due to a combined effect of changing differential pressure from 35 MPa to 27 MPa and injecting CO2-rich brine. For the more clay rich sample, the moduli decreased by even larger percentages (39.0% and 20.1%, respectively), which could have significant implications on time-lapse seismic data and subsequent estimations of injected CO2 volumes.
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DEEP WATER GULF OF MEXICO PORE PRESSURE ESTIMATION UTILIZING P-SV WAVES FROM MULTICOMPONENT SEISMIC IN ATLANTIS FIELD
Jeffrey Chung-Chen Kao, MSGeoSci
University of Texas at Austin, December 2009
Supervisor: Robert H. Tatham
103 pages, 63 references
Overpressure, or abnormally low effective pressures, is hazardous in drilling operations and construction of sea-bottom facilities in deepwater environments. Estimation of the locations of overpressure can improve safety in these operations and significantly reduce overall project costs. Propagation velocities of both seismic P and S wave are sensitive to bulk elastic parameters and density of the sediments, which can be related to porosity, pore fluid content, lithology, and effective pressures. Overpressured areas can be analyzed using 4C seismic reflection data, which includes P-P and P-SV reflections. In this thesis, the effects on compressional (P) and shear (S) wave velocities are investigated to estimate the magnitude and location of excess pore pressure utilizing Eaton’s approach for pressure prediction (Eaton, 1969).
Eaton’s (1969) method relates changes in pore pressure to changes in seismic P-wave velocity. The underlying assumption of this method utilizes the ratio of observed P-wave velocity obtained from areas of both normal and abnormal pressure. This velocity ratio evaluated through an empirically determined exponent is then related to the ratio of effective stress under normal and abnormal pressure conditions. Effective stress in a normal pressured condition is greater than the effective stress value in abnormally overpressured conditions. Due to an increased sensitivity of variations in effective pressure to seismic interval velocity, Ebrom et al. (2003) employ a modified Eaton equation to incorporate the S-wave velocity in pore pressure prediction.
The data preparation and subsequent observations of seismic P and S wave velocity estimates in this thesis represent a preliminary analysis for pore pressure prediction. Six 2D receiver gathers in the regional dip direction are extracted from six individual ocean-bottom 4C seismic recording nodes for P-P and P-SV velocity analysis. The receiver gathers employed have minimal pre-processing procedures applied. The main processing steps applied were: water bottom mute, 2D rotation of horizontal components to SV and SH orientation, deconvolution, and frequency filtering. Most the processing was performed in Matlab with a volume of scripts designed by research scientists from the University of Texas, Bureau of Economic Geology.
In this thesis, fluid pressure prediction is estimated utilizing several 4C multicomponent ocean-bottom nodes in the Atlantis Field in deepwater Gulf of Mexico. Velocity analysis is performed through a ray tracing approach utilizing P-P and P-SV registration. A modified Eaton’s Algorithm is then used for pore pressure prediction using both P and S wave velocity values.
I was able to successfully observe both compressional and shear wave velocities to sediment depths of approximately 800 m below the seafloor. Using Hamilton (1972, 1976) and Eberhart-Phillips et al. (1989) regressions as background depth dependent velocity values and well-log derived background effective pressure values from deepwater Gulf of Mexico, I am able to solve for predicted effective pressure for the study area. The results show that the Atlantis subsurface study area experiences a degree of overpressure.
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A FLUID INCLUSION AND CATHODOLUMINESCENCE APPROACH TO RECONSTRUCT FRACTURE GROWTH IN THE TRIASSIC-JURASSIC LA BOCA FORMATION, NORTHEASTERN MEXICO
Autumn Leigh Kaylor, MS Geo. Sci.
University of Texas at Austin, December 2011
Supervisors: Peter Eichhubl and Stephen Laubach
202 pages, 114 references, 27 tables
Opening-mode fracture shapes are typically the result of brittle deformation and proportional growth in fracture height, length, and width. Based on the typical fracture shape, it is assumed that fracture tips are free to propagate in all directions. Some natural rock fractures have been shown to form as a result of slow non-elastic deformation processes. Such fractures may propagate to a finite length or height and accommodate further growth by aperture widening only. To determine the growth conditions of a fracture in the Triassic-Jurassic La Boca Formation of northeastern Mexico and to test fracture growth models, I combined fluid inclusion microthermometry and SEM-based cathodoluminescence cement texture analysis to determine the relative timing of fracture cement precipitation and related fracture opening for five samples collected along its trace.
Fracture growth initiated at a minimum age of 70 Ma as two separate fractures with branching fracture tips that coalesced to a single continuous fracture under prograde burial conditions at a minimum age of 54 Ma. At this stage, fracture growth was accommodated by both propagation (i.e. increase in trace length) and by an increase in aperture during maximum burial and early exhumation. Samples collected at the fracture tips recorded temperatures reflecting fracture opening starting with maximum burial at a minimum age of 48 Ma at one tip and of 38 Ma at the other tip. Synkinematic fluid inclusions in crack-seal cement track continued fracture opening close to the fracture tips without a concurrent increase in trace length after 38 Ma until about 21 Ma.
I attribute the observed change in fracture growth mechanism to a change in material response. The stage in aperture increase without propagation corresponds to an increase in elastic compliance or in non-elastic flow properties. Non-elastic flow can be attributed to solution-precipitation creep of the host rock. Dissolution of host quartz grains and subsequent quartz precipitation is consistent with the abundance of quartz fracture cement formed during exhumation. Cement textures from fractures in the La Boca Formation mimic those found in subsurface core, which allows application of the results to a variety of geologic environments.
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UNRECOGNIZED COMPLEXITIES OF METAMORPHISM : CRYSTALLIZATION KINETICS, REACTION AFFINITY, AND GEOCHRONOLOGY
Eric David Kelly, Ph.D.
University of Texas at Austin, December 2011
Supervisors: William D. Carlson and Richard A. Ketcham
370 pages, 159 references, 12 tables
Unrecognized metamorphic complexities can produce erroneous interpretations when using equilibrium thermodynamics and isotope geochronology. Universally em-ployed methods for determining pressure-temperature conditions during regional meta-morphism are based on the assumption of chemical equilibrium, and geochronology in metamorphic rocks can suffer from cryptic redistribution of isotopes. In this research, the scales of disequilibrium in regionally metamorphosed rocks and the effects of garnet resorption on Lu-Hf garnet ages were examined through numerical simulations of these processes.
Concerning scales of disequilibrium, thirteen porphyroblastic datasets, previously measured using X-ray computed tomography, were examined by numerically simulating diffusion-controlled nucleation and growth of garnet while tracking chemical potential gradients to determine reaction affinity Ar (-ΔrG). Maximum nucleation rates are 10-13.6-10-9.8 nuclei cm-3 s-1, interfacial energies are 0.004-0.14 J m-2 assuming shape factors of 0.1-1.0, and Al intergranular diffusion (QD = 140 kJ mol-1) is 10-14.4-10-11.1 m2 s-1 at 600 °C. Limitations in determining crystallization kinetics arise from difficulties in constraining rock-specific properties (e.g., porosity and Al solubility). Ar at the time and location of nucleation is 0.4-5.9 kJ mol-1 of 12-oxygen garnet (ΔT = 4.0-62.0 °C) for the earliest nuclei, and 5.3-29.0 kJ mol-1 (ΔT = 50-125 °C) for nucleation at maximum Ar. The results demonstrate potential for delayed nucleation and metastability that can generate spurious interpretations.
The timing of metamorphic events is also critical for understanding geologic history. In the Makhavinekh Lake Pluton aureole, Labrador, garnet resorption caused redistribution of Lu and loss of Hf from consumed rims, creating spuriously young ages. Garnet-ilmenite Lu-Hf geochronology using bulk separates yields apparent ages that young toward the contact from 1876 ± 21 Ma (4025 m) to 1396 ± 8 Ma (450 m). Toward the contact, garnet crystals are progressively more resorbed. Numerical modeling was used to test retention of Lu and loss of Hf during resorption as the dominant control on age. More resorption and Lu retention produce younger apparent ages (false ages). Application of the model to the aureole yields model ages from 1850 Ma to 1374 Ma, younging toward the contact. Thus, Lu-Hf geochronology applied to resorbed garnets requires careful examination of Lu zoning.
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EXAMINING SUPERCRITICAL CO2 DISSOLUTION KINETICS DURING CARBON SEQUESTRATION THROUGH COLUMN EXPERIMENTS
Molly Elizabeth Kent, MSGeoSci
University of Texas at Austin, August 2011
Supervisor: Phil Bennett
148 pages, 25 references, 9 tables
Carbon sequestration is a method of capturing and storing excess anthropogenic CO2 in the subsurface. When CO2 is injected, the temperature and pressure at depth turn it into a supercritical (SC) fluid, where density is that of a liquid, but viscosity and compressibility resemble a gas. Ultimately the SC CO2 is trapped at depth either by low permeability sealing layers, by reactions with minerals, or by dissolving into fluids. The injected CO2 is buoyant and initially exists as a non-aqueous hydrophobic layer floating on top of the subsurface brine, up against the upper sealing formation, but over time it will dissolve into the brine and potentially react with minerals. The details of that initial dissolution reaction, however, are only poorly understood, and I address three basic questions for this research: What is the fundamental kinetics of SC CO2 dissolution into water? How fast does dissolved CO2 diffuse away from the source point? And what geochemical conditions influence the dissolution rate?
To answer these questions I employed a high pressure flow-through approach using a column packed with coarse quartz sand. The system was both pressure and temperature controlled to have either liquid or SC CO2 present, and was typically run at 100 Bar, 0.5 to 2.5 mls/min, and 28-60°C. After establishing the hydraulic parameters for the column using two conservative tracers (Br, As), injections (5 and 20 µl) were made either as aqueous solutions equilibrated to high pressure CO2, or as pure liquid or SC CO2 into 0.1 mmol NaOH. For all experiments the pH of the system was monitored, and [CO2] over time was calculated from those data.
For injections of brine with dissolved CO2, transport was conservative and was nearly identical to the conservative tracers. The CO2 quickly mixes in the column and does not react with the quartz. The liquid and SC CO2 injections, however, do not act conservatively, and have a very long tailing breakthrough curve that extends to tens of pore volumes. I hypothesize that the SC CO2 is becoming trapped as a droplet or many droplets in the pore spaces, and the long breakthrough tail is related either to the rate of dissolution into the aqueous phase, the diffusion of dissolved CO2 away from the phase boundary, or the reaction with the NaOH, limited to the narrow contact zones in the pore throats. Because of the speed at which acid-base reactions occur (nanosecond kinetics), I infer that the rate limiting step is either surface dissolution or diffusion. From plots of ln[CO2] v. time I obtained values for k, the specific rate of the dissolution reaction R= -k[CO2]. No trend for k was seen with respect to changes in temperature, but k did show a trend with respect to changing flow rate. k increased from an average value of 3.05x10-3 at 0.5 ml/min to an average value of 3.38x10-3 at 1.6 ml/min, and then held constant at the higher flow rates, up to 2.5 ml/min. I interpret these data to show that at low flow rates, the reaction is diffusion limited; the fluid nearest the contact zone becomes saturated with dissolved CO2. At higher flow rates, the fluid is moving fast enough that saturation cannot occur, and the kinetics of the dissolution reaction dominate.
Simple geometric models indicate that the CO2/water interface is shaped like a spherical cap, indicating that the snapped-off CO2 is forming a meniscus in the pore throat, limiting the surface area across which dissolution can occur.
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TRANSACTION COST AND HOST COUNTRY'S OPPORTUNISTIC BEHAVIOR IN OIL E&P PROJECT
Tae Eun Kim, M.A.
University of Texas at Austin, May 2011
Supervisor: Christopher J. Jablonowski
73 pages, 51 references, 11 tables
The purpose of this paper is to understand why a host country (HC) shows ex post opportunistic behaviors in E&P projects and frequently forces international oil companies (IOCs) to renegotiate previously signed contracts. This research employs the concept of asset specificity and hold-up problem in transaction cost economics (TCE). It then examines the unique characteristics of E&P projects, HC's opportunistic behaviors, and IOCs' safeguards. For a case study analyzing the implications between the economic theory and HC's ex post opportunism in oil E&P project, I have selected Kazakhstan. The result is that HC's ex post opportunism can be explained by a hold-up problem resulting from IOCs' sunk investments and the unique characteristics of the oil E&P industry. When IOCs' important capital assets become sunk investments and the price of oil increases rapidly, HC has a strong incentive to appropriate IOCs' profits through ex post opportunism. Yet at the same time, HC must consider the damage to its reputation when deciding the extent and ways of its ex post opportunistic behaviors in oil E&P projects.
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EVOLUTION OF A REGIONALLY EXTENSIVE EVAPORITE REMOVAL PALEOKARST COMPLEX : MISSISSIPPIAN MADISON GROUP, WYOMING
Travis T. Kloss, M.S. Geo. Sci.
University of Texas at Austin, December 2011
Supervisors: Charles Kerans and Christopher Zahm
137 pages, 48 references, 2 tables
Paleokarst systems owe their complex geometries to the interaction between the karst aquifers and the host rock being dissolved. The majority of paleokarst research to date has considered dissolution of carbonate strata (James and Choquette 1987), but rapid and extensive dissolution of interstratified evaporites can be an important if largely undocumented style of paleokarst that may play an important role in near-surface environmental settings as well as providing a unique style of reservoir heterogeneity in the subsurface (Sando 1967, 1974, 1988; Smith et al. 2004). This study is designed to answer the question, "How do we recognize evaporite paleokarst as distinct from standard meteoric carbonate paleokarst?" using spectacular, laterally continuous exposures in the upper Madison Formation within Bighorn Canyon, Wyoming.
Key characteristics of the Madison intrastratal evaporite karst complex were documented and contrasted with the top-Madison surficial karst system resulting in a suite of data that includes detailed section measuring, facies mapping using high resolution photo panels and ground based LiDAR for control. Hand samples, thin sections and x-ray diffraction analysis also contributed to this study. High resolution mapping of key surfaces, karst facies and petrophysical properties were used to develop a stepwise evolutionary model of the evaporite removal paleokarst complex. The interplay between surficial karstification, solution enhanced fractures, subsurface intrastratal evaporite dissolution, collapse and infill, were considered in constructing this model.
Similar to standard meteoric paleokarst systems, the Madison evaporite paleokarst has been divided into 7 distinct karst "facies" including laminated cave floor fill, roof collapse chaotic breccias, and suprastratal dissolution complexes. Features proposed to be unique to evaporite paleokarst that will aid in future studies are (1) presence of relic gypsum breccia clasts within cave-fill facies, (2) the near absence of cave pillars or roof touch down within the chaotic breccia zones, indicating removal of a laterally extensive soluble stratum, (4) a striking absence of sub-cave floor breccias or fractures, (5) a distinct breccia matrix consisting of primarily autochthonous detrital dolomite with a minor component of allochthonous detrital clays from the overlying Amsden, suggesting that the bulk of the breccia matrix is locally sourced insoluble residue from evaporite dissolution, and finally (6) close facies associations of the depositional sequence suggesting that evaporites were a likely part of the original stratigraphic record in the Madison. These criteria are considered to be a solid starting point for an evaporite paleokarst model and should assist in the recognition of similar paleokarst breccias in the ancient rock record.
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WIND ENERGY IN TURKEY: POTENTIAL AND ECONOMIC VIABILITY
Zafer Korkulu, M.A.
University of Texas at Austin, May 2011
Supervisor: Charles Groat
72 pages, 44 references, 24 tables
Turkey wants to encourage renewable electricity generation to reduce dependence on imported natural gas and meet its highly growing power demand. The government's objective is to increase the share of renewable resources in electricity generation to at least 30 percent by 2023, and the specific target for the installed wind energy capacity is 20 GW by that date. Fortunately, Turkey has an enormous wind energy potential to exploit for electricity generation. When from "good" to "outstanding" wind clusters are taken into account, the overall technical wind power generation capacity in Turkey is calculated to be nearly 48 GW. In this context, this thesis investigates whether policy instruments in the Turkish regulatory frame contribute to economic viability for wind power projects or not. The financial results point out that an electricity price of 7.3 USD cent/kWh, which is the guaranteed price for wind power generation by current regulations, does not make a typical onshore wind power plant located in a "good" windy resource economically viable. However, when locally produced wing blades and turbine towers are used in the project, the purchase price increases to 8.7 USD cent/kWh, and the project becomes economically viable. As a result, the local content element introduced in recent regulations promotes wind energy investments and helps government to reach its renewable target for 2023.
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A FEASIBILITY STUDY ON UTILITY-SCALE SOLAR INTEGRATION IN THE KINGDOM OF SAUDI ARABIA
Barthram Krishnamoorthy, MA
University of Texas at Austin, May 2010
Supervisor: David Spence
79 pages, 54 references, 20 tables
Due to the vast fossil fuel wealth, the country of Saudi Arabia is experiencing a dramatic growth in both population and GDP. Therefore there is a growing demand for water and energy to meet these needs. All of the electricity that is generated is sourced from crude oil and natural gas. All natural gas production is used domestically and there are no net imports or exports. Due to many constrains on the natural gas supply, there is a slow shift in the generation mix going towards crude oil based power generation. This study assessed the viability of utility scale solar integration into the Saudi Arabian electric mix to potentially relieve some demand pressure for natural gas consumption as well as reduce green house gas emissions. Parabolic trough concentrated solar power technology was chosen as the primary technology for utility scale integration. A total of five scenarios were calculated. The scenarios include the following, base case, 5%, 10%, 15%, 20% solar integration in terms of installed capacity. Two sets of net present values were calculated. The net present values of each scenario were calculated. A second set of net present values was calculated with a projected increase in electricity prices. The natural gas and crude oil offset from the four solar integration scenarios were calculated using the base case forecasted natural gas and crude oil consumption from power generation. As expected, natural gas and crude oil consumption decreased when there was an increase in solar integration. The expected carbon dioxide offsets were calculated for each scenario. There was a decrease in carbon dioxide emission as solar integration was increased. Finally, all of these analyses were used as criteria for a decision analysis using the analytical hierarchy process. Depending on the decision maker's importance on the determined criteria, solar integration in the Kingdom of Saudi Arabia is achievable.
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THE CHALLENGES TO INTEGRATING WIND ENERGY: A STUDY OF ERCOT'S ABILITY TO INTEGRATE SUBSTANTIAL AMOUNTS OF WIND ENERGY BY 2030
Nathan Richard Lapierre, M.A.
University of Texas at Austin, May 2010
Supervisor: Michael Webber
105 pages, 78 references, 4 tables
The wind energy industry in the U.S. has seen robust growth within the last two decades. The amount of renewable resources available throughout the U.S. is substantial, and as renewable energy penetration approaches a significant proportion of total electricity generation, grid operators and utilities will be presented with a myriad of challenges.
Such is the case in wind' rich Texas, where the rate of wind installations surpasses every other state and rivals that of China. By the end of 2009, the ERGOT region of Texas had approximately 9000 MW installed, serving 6.5% of the annual electricity load1. The intermittent nature of wind energy can place a burden on existing generators as they are increasingly relied on to provide regulation of power, frequency control and back-up energy services when wind production is low.
Exacerbating the difficulty of integrating wind energy is the mismatch of wind generation and electricity demand. Although Texas is blessed with plentiful wind resources, the majority of energy produced typically occurs at night when electricity demands are low. The result is transmission congestion that prevents cost effective generators from serving load. Despite these integration difficulties, ERGOT is paving the way forward with transformative infrastructure plans and proactive rulemaking.
This report provides a background on the state of the wind energy industry in the U.S., with a review of power system operation strategies and wind integration best practices. With that context, this study concludes that ERCOT's electricity market operations, transmission plans, and Texas' renewable energy policies will act to reasonably and reliably accommodate wind generation capacity that serves over 15% of annual load by 2030.
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IN SITU MELT GENERATION IN ANATECTIC MIGMATITES AND THE ROLE OF STRAIN IN PREFERENTIALLY INDUCING MELTING
Jamie Sloan Levine, Ph.D.
University of Texas at Austin, August 2011
Supervisor: Sharon Mosher
184 pages, 207 references, 8 tables
Deformation and partial melting have long been recognized to occur together, but differentiating which actually occurred first has remained enigmatic. Prevailing theories suggest that partial melting typically occurs first, and deformation is localized into melt-rich areas because they are rheologically weak. However, evidence from three different areas, suggests the role of strain has been underestimated in localizing partial melting.
Granitic gneisses from the Llano Uplift, central Texas, provide evidence for partial melting occurring within small-scale shear zones and surrounding country rocks, synchronously. In the field, shear zones appear to contain relict melt, whereas the country rock does not provide macroscopic evidence for partial melting. However, detailed microstructural investigation of shear zones and country rocks indicates the same density of melt microstructures, in both rock types. Melt microstructures are important for understanding the full melting history of a rock and without detailed structural and petrographic analysis, erroneous conclusions may be reached.
The Wet Mountains of central Colorado provide evidence for synchronous partial melting and deformation, with each process enhancing the other. Throughout the Wet Mountains, deformation is concentrated in areas where melt producing reactions occurred, and melt appears to be localized along deformation-related features. Melt microstructures present within the Wet Mountains correlate well with crustal-scale plutons and magmatic bodies and provide a proxy for crustal-scale melt flow.
Granulite-facies migmatites of the Albany-Fraser Orogen, southwestern Australia, have undergone partial melting, synchronous with three phases of bidirectional extension. Four major groups of leucosomes, including: foliation-parallel, cross-cutting, boudin neck and jumbled channelway leucosomes and late pegmatites were analyzed via whole-rock geochemistry, and there is evidence for fluid-saturated and -undersaturated biotite- and amphibole-dehydration melting.
Migmatites from these three locations contain pseudomorphs of melt along subgrain and grain boundaries, areas of high dislocation density, in quartz and plagioclase. For these rocks that involve multicomponent systems, the primary cause for preferential melting in high strain locations is enhanced diffusion rates along the subgrain boundary because of pipe diffusion or water associated with dislocations.
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GBM & MRJ: TWO OIL PRICING MODELS’ COMPARISON AND EFFECT ON PROJECT NPV CALCULATION
Zhizhen Liu, M.A
University of Texas at Austin, May 2009
Supervisor: Leon S Lasdon
Co-Supervisor: Christopher J Jablonowski
107 pages, 48 references
This thesis constructs and investigates two widely applied oil pricing models: Geometric Brownian Motion (GBM) and Mean Reversion Motion with Jumps (MRJ). After comparing the forecast results from two models and applying them in the project Net Present Value calculation under offshore and onshore scenarios, a conclusion is drawn out that the MRJ model outperforms the GBM model in both situations and delivers more accurate outcomes in future price prediction and project NPV calculation in petroleum project management.
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GEOMORPHOLOGY AND STRATIGRAPHIC EVOLUTION OF THE GIANT FORESETS, TARANAKI BASIN, NEW ZEALAND
Thomas Daniel Lovitz, MSGeoSci
University of Texas at Austin, August 2009
Supervisors: William Fisher, Lesli Wood
117 pages, 32 references, 2 tables
The Giant Foresets Formation is located in Taranaki Basin, offshore west coast North Island, New Zealand. Despite a complex structural history in the Basin, the Giant Foresets Formation was deposited during the relative quiescence of the Pliocene and Pleistocene. Giant Foresets Formation deposits were studied in the Northern Graben using a subset of a 1600km2 3D seismic survey which focused interest on two large, deeply incised canyon systems of differing ages. Deposition and canyon incision were influenced by relative sea level changes. Progradation occurred during relative lowstands, while canyon formation occurred during periods of sea level high stand due to instability of the slope. Clinoforms prograded during periods of lowstand when significant quantities of sediment were supplied to the slope. During highstand, with little to no sediment supply, slope instability caused failures of the slope and headward erosion of the canyon up through previously deposited slope and topset facies. The Northern Graben to the west and volcanic highs to the east acted to funnel the canyons up its axis. The older major canyonization headwardly eroded until the canyon reached a point where it was no longer bound by the fault to the west and the canyon branched out into feeder canyons which bifurcate into smaller and smaller channels towards the south until they reach their updip termination. Canyon filling within the dataset occurred during lowstand when renewed sediment influx created localized, prograding clinoforms within the canyon. Headwardly eroded sediment is likely to be deposited at the mouth of the canyon and partially onlap the canyon; although, there is no evidence of this within the seismic volume. Canyon fill has geometries and characteristics similar to that of prograding clinoforms and was deposited during lowstand. While structure played a minor role in development of the Giant Foresets Formation, the majority of its depositional history is controlled by sediment supply.
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TO CONSERVE OR CONSUME : BEHAVIOR CHANGE IN RESIDENTIAL SOLAR PV OWNERS
Kristine Lee McAndrews, M.A.
University of Texas at Austin, December 2011
Supervisor: Varun Rai
63 pages, 16 references, 16 tables
A survey of residential solar photovoltaic (PV) adopters in Texas was administered and the results are presented and discussed. A 40% response rate was achieved and 365 complete responses were received. In addition to demographics, the survey uncovered aspects related to the decision-making process, information search, financial attractiveness of PV, and post-installation experience. Peer-effects did not have a large influence on the adoption of residential PV in Texas, but the potential for increasing the number of communication/information channels to increase the adoption rate of PV exists. Adopters experienced little uncertainty at the time of PV installation because sufficient dependable information was available during the search process. Overall, they are satisfied with PV.
Contextual factors, such as income and the ability to purchase a PV system rather than lease one, influence behavior. Those who decreased electricity consumption post-adoption were more motivated to adopt by environmental concern and a general interest in energy than those who increased electricity consumption post-adoption. Those who experienced behavior changes also experienced an increase in awareness of electricity use post-adoption, while those who did not experience a behavior change reported no change in awareness post-adoption. Change in awareness of electricity use is less dependent on the attitudinal and contextual factors, such as environmental concern, motivation for adoption, age, and income, that influence consumption change.
The potential for further analysis of the survey results is great and will likely yield additional conclusions about the consequences of the adoption of PV. Coupling the survey results with historical electricity bill data will yield stronger conclusions about behavior change. Surveying geographical areas outside of Texas is recommended.
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AN EVALUATION OF QUARTZ-INCLUSION BAROMETRY BY LASER RAMAN MICROSPECTROMETRY: A CASE STUDY FROM THE LLANO UPLIFT OF CENTRAL TEXAS
Emily Allen McDowell, M.S. Geo. Sci.
University of Texas at Austin, August 2009
Supervisor: William D. Carlson
208 pages, 25 references, 6 tables
A new barometric technique measuring stored stress in quartz inclusions via laser Raman microspectrometry was employed in an attempt to elucidate the extent of high-pressure (HP) metamorphism in the Llano Uplift of central Texas. Rare lithologies within the Llano Uplift contain mineralogical evidence of HP metamorphism (pressures from 1.4 to 2.4 GPa at temperatures from 650 to 775°C), but much of the uplift is composed of felsic gneisses lacking any HP signature; these felsic gneisses may never have transformed to HP assemblages, or they may have been thoroughly overprinted by later low-pressure events. Barometry via laser Raman microspectrometry computes entrapment pressure for a quartz inclusion in garnet from measurement of the displacements of its Raman peak positions from those of a quartz standard at atmospheric pressure. Quartz inclusions in garnets that grew in felsic gneisses under HP conditions should retain HP signatures, despite later overprinting. Application of the Raman microspectrometry technique should therefore allow barometry of previously uncharacterizable rocks.
For two localities in the Llano Uplift, entrapment pressures from Raman barometry (0.6-0.7 GPa and 0.2-0.3 GPa) were substantially lower than pressures expected based on conventional barometers (1.4 GPa and 1.6-2.4 GPa). This absence of any HP signatures in the Llano rocks contrasts with more successful applications of the Raman technique by previous workers in high P/T blueschist-facies rocks. A key difference in the Llano rocks is that they reached peak temperatures at which intracrystalline diffusion in garnet, driven by compositional gradients produced during growth, had noticeable effects: complete homogenization of growth zoning had occurred in the locality that produced the greatest discrepancies between Raman and conventional pressures, and modest relaxation of zoning occurred in the locality with the smaller discrepancies. The failure of the Raman technique to recover pressures consistent with conventional barometry in the Llano Uplift is therefore attributed to relaxation of stress on the quartz inclusions as the result of intracrystalline diffusion within the garnet. This conclusion suggests that use of the Raman barometric technique must be restricted to rocks whose time-temperature histories produce only very limited intracrystalline diffusion in garnet, typically those rocks whose peak metamorphic temperatures fall at or below upper amphibolite-facies conditions.
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EXPRESSIONS AND IMPLICATIONS OF SEDIMENT TRANSPORT VARIABILITY IN SANDY RIVERS
Brandon John McElroy, Ph.D.
University of Texas at Austin, December 2009
Supervisor: David Mohrig
128 pages, 142 references, 2 tables
This dissertation presents an investigation of the effects of a stochastic component of sediment transport in sandy rivers in an attempt to gain information about the transport system and its implications for the evolution of Earth's surface topography. First, a method for characterizing the geometries of bed forms is introduced and compared to previously proposed methods. This new method is then implemented on a field dataset as well as laboratory dataset and the results are compared to those obtained by traditional methods. Second, a method for characterizing the dynamic evolution of the bed geometries is demonstrated. It produces a velocity scale, the mean migration rate of the bed topography, and a deformation scale, the evolutionary departures of the bed topography from pure migration. These scales are calculated for the field and laboratory data and are compared. The flux of bed sediment is then shown to depend on the stochastic component of bed evolution. The fluxes for each dataset are calculated, they are related to the environmental conditions causing the transport of sediment, and suggestions are made for the design of field campaigns that attempt to measure sediment transport by repeated surveys of bed topography. Finally, the implications of stochasticity for sediment transport are investigated. A null hypothesis is formulated for topographic change by a stochastic process. Then the effects of measurement and field collection methods on the null hypothesis are evaluated. The most important prediction is non-trivial behaviors in measurable rates of surface change at short timescales. This prediction is then evaluated with field data from a growing sandy channel network whose behaviors can be determined at timescales of decades to centuries (dendrochronology), tens of thousands of years (cosmogenic radiochemistry), and hundreds of thousands to millions of years (age of channel system and sediments through which it cuts). These three investigations create a coherent account of the expressions and implications of variability in the transport of sediment, and therefore the evolution of topography, in sandy river systems that can then be generalized to changes across Earth's surface.
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PROVENANCE OF THE SOUTH TEXAS PALEOCENE-EOCENE WILCOX GROUP, WESTERN GULF OF MEXICO BASIN: INSIGHTS FROM SANDSTONE MODAL COMPOSITIONS AND DETRITAL ZIRCON GEOCHRONOLOGY
Glen Nelson Mackey, III, MSGeoSci
University of Texas at Austin, August 2009
Supervisor: Kitty L. Milliken
155 pages, 181 references, 57 tables
Sandstone modal compositions and detrital zircon U-Pb analysis of the Paleocene-Eocene Wilcox Group of the southern Gulf Coast of Texas indicate long-distance sediment transport primarily from volcanic and basement sources to the west, northwest and southwest.
The Wilcox Group of south Texas represents the earliest series of major post-Cretaceous pulses of sand deposition along the western margin of the Gulf of Mexico (GoM). Laramide basement uplifts have long been held to be the provenance of the Wilcox Group, implying that initiation of basement uplifts was the driving factor for this transition from carbonate sedimentation to clastic deposition. To determine the provenance of the Wilcox Group and test this conventional hypothesis, 40 thin sections were point-counted using the Gazzi-Dickinson method to determine sandstone composition and 10 detrital zircon samples were analyzed by LA-ICP-MS to determine U-Pb age spectra for each of the sampled areas.
Modal data for sand grain populations suggest mixed sources including basement rocks, magmatic arc rocks and subordinate sedimentary rocks for the Wilcox Group. Zircon age spectra for these sandstones reveal a complex grain assemblage derived from older sediments and crystalline rocks ranging in age from Archean to Cenozoic. Sediment was primarily derived from Laramide uplifted crystalline blocks of the central and southern Rocky Mountains, the Cordilleran arc of western North America, and arc related extrusive and intrusive igneous rock of northern Mexico. Comparisons of Upper and Lower Wilcox zircon age spectra show that more arc related material was deposited in the Lower Wilcox, whereas more basement material was deposited in the Upper Wilcox.
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SEQUENCE STRATIGRAPHIC ANALYSIS OF MARGINAL MARINE SABKHA FACIES: ENTRADA SANDSTONE, FOUR CORNERS REGION
Glenn Kenneth Makechnie, MSGeoSci
University of Texas at Austin, August 2010
Supervisor: Gary Kocurek
66 pages, 48 references
The Middle Jurassic Entrada Sandstone of the Four Corners region, USA, is composed predominantly of very fine-grained, red, silty sandstone with poorly defined sedimentary structures. The origin of this facies is enigmatic, even though it is common both on the Colorado Plateau and globally, and is spatially situated between deposits recording unambiguous marine and aeolian environments. Eleven sections were measured along an 85 km transect from the Blanding Basin in southeastern Utah to the San Juan Basin in northwestern New Mexico. Outcrop and laboratory analyses distinguish eight facies: (1) silty shale, (2) shallow subaqueous reworked, fine- to medium-grained sandstone, (3) brecciated, very fine-grained sandstone, (4) crinkly laminated, very fine-grained sandstone with preserved wind ripples and abundant silty laminae, (5) weakly laminated, fine-grained sandstone with occasional silty laminae, (6) planar-laminated, fine-grained, wind-rippled sandstone, (7) cross-stratified, fine- to medium-grained aeolian cross-stratified sandstone, and (8) micritic limestone. Lateral and vertical relationships of these facies show a proximal to distal transition from cross-bedded wind-lain facies to loess-dominated sabkha facies with increasing abundance of water-lain facies basinward. The well known Todilto Limestone (facies 8) is situated stratigraphically below loess-dominated sabkha facies (facies 4 and 5) within the Entrada Sandstone, reinforcing previous interpretations that the unit represents a catastrophic flooding event and not a local groundwater flux.
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CHARACTERIZING GROUNDWATER-SURFACE WATER INTERACTIONS IN A REGULATED RIVER USING ELECTRICAL RESISTIVITY
Michael Sean Markowski, B.S.
University of Texas at Austin, May 2010
Supervisor: Meinhard B. Cardenas
31 pages, 16 references, 1 table
The regular release of water from Tom Miller Dam, Austin, TX causes daily stage oscillations in the Colorado River that persist downstream over long distances. Fifteen km downstream from the dam, at the Hornsby Bend Center for Environmental Research, river stage rises and falls by nearly a meter every day. The objective of this research project was to test a method of electrical resistivity imaging that detects and characterizes the effects of this stage fluctuation on groundwater/ surface water interactions. Two separate resistivity methods are utilized in this study. A stationary transect is run across the width of the river. Data collection along this transect is repeated back-to-back for approximately 24 hours to capture the 24 hour cycle of the stage oscillation. Continuous Resistivity Profiling (CRP) was also used along two separate transects each about 400 m. The two transects were repeated ten times, at 2.5 hour intervals to correspond with the 24 hour stage oscillation. Stacking the tomographs from the stationary transect into a time-lapse representation shows significant changes in resistivity in the uppermost 2.0 m of substrate located immediately below the sediment-water interface. Results from the CRP profiles indicate that this exchange can be detected over an even larger spatial scale. These results show electrical resistivity as a powerful tool for better understanding the effects of oscillating river stage on hyporheic processes.
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PETROLOGY OF THE COAST RANGE OPHIOLITE NEAR SAN SIMEON, CALIFORNIA: IMPLICATIONS FOR TECTONIC SETTING
Paul Michael Mehring, M.S. Geo. Sci.
University of Texas at Austin, August 2009
Supervisor: Mark Cloos
353 pages, 150 references, 13 tables
A fragment of the middle Jurassic (165.55 ± 0.12 Ma) Coast Range ophiolite (CRO) is present near San Simeon, San Luis Obispo County, California. Rocks from different levels of the ophiolite sequence are exposed along 5.5 km of fresh, wave-cut coastline between Ragged Point and Piedras Blancas Point. The ophiolite crops out with ultramafics in the north and volcanics and chert in the south. For this study 238 samples were examined petrographically. Twenty samples were selected for electron probe microanalysis (EPMA) in order to determine mineral composition of plagioclase, clinopyroxene, orthopyroxene, olivine, and chromian spinel. Nine samples from the diabase sill complex were selected for whole-rock geochemistry.
Ragged Point (~0.5 km length of exposure) has abundant ultramafic cumulate rocks that include serpentinized dunite. The ultramafics are intruded by meter-thick mafic sills. Breaker Point (~1.5 km of exposure) has abundant ultramafic and mafic cumulate rocks that include serpentinized dunite, wehrlite, olivine clinopyroxenite, clinopyroxenite, websterite, gabbro (norite), and clinopyroxene troctolite. As at Ragged Point, the cumulate ultramafics are intruded by meter-thick mafic sills. Point Sierra Nevada (~2.0 km of exposure) has hornblende-bearing (up to 15% estimated modal abundance) gabbro(norite) and massive hornblende gabbro in fault contact with a sheeted diabase sill complex. The gabbroic rocks are cross-cut by swarms of 3-25 centimeter hornblende-rich (up to 40% modal abundance in ~200 m length of exposure) diabase intrusions. Point Piedras Blancas (~1.8 km of exposure) has volcanics including pillow and breccia flows faulted against thin-bedded chert. Meter-wide slices of residual harzburgite are present within fault zones at both Ragged Point and Point Sierra Nevada. A tall (>700 meters) magma chamber must have been present to explain the measured thickness of ultramafic and mafic cumulates.
The field observations indicate that cumulate ultramafics (dunite, wehrlite, olivine clinopyroxenite, clinopyroxenite, and websterite) are followed up-sequence by cumulate gabbroic rocks and then massive hornblende gabbro. This order indicates a crystallization sequence of olivine ± chromian spinel; then olivine + clinopyroxene ± orthopyroxene ± hornblende ± chromian spinel; then plagioclase + clinopyroxene ± olivine ± orthopyroxene ± hornblende; followed by plagioclase + hornblende ± clinopyroxene ± Fe-Ti oxide. Compositional ranges of minerals are consistent with formation from a single differentiating mafic magma: plagioclase (An98 to An30); clinopyroxene (Mg#: 91 to 79); orthopyroxene (Mg#: 85 to 75); olivine (Fo91 to Fo71); and chromian spinel (Cr#: 48 to 82). The new data are similar to those reported for other CRO fragments.
The appearance of low-TiO2 clinopyroxene before highly calcic plagioclase in the crystallization sequence and the relative abundance of orthopyroxene in cumulate ultramafic and mafic rocks indicate magma with a high MgO/SiO2 ratio and suggest that the differentiating mafic magma was extracted from asthenosphere that experienced moderate degrees of partial melting (15 to 30%). A moderate degree of partial melting is greater than expected for those at open-ocean-spreading ridges (~15%), and is explained as due to the addition of subducted H2O.
Selected samples from the sheeted diabase sill complex are geochemically similar to CRO volcanics at Del Puerto, Llanada, and Point Sal. Their compositional range for major-, trace-, and rare-earth-elements suggest that the San Simeon ophiolite formed from a differentiating parental magma, which had a component of subducted material. The addition of LIL-enriched hydrous fluids (and possibly subducted sediment) from the down-going plate fluxed the asthenosphere resulting in moderate degrees of partial melting. The San Simeon CRO is interpreted to be an on-land slab of ocean crust formed at a slow-spreading center (few cm/yr) above a west-directed subduction zone. A rifting-arc or back-arc environment, similar to the Mariana Trough (Deep Sea Drilling Project Leg 60), is proposed for the San Simeon ophiolite.
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SOUTHWEST U.S. PALEOCLIMATE OVER THE PAST 30 KY : INSIGHTS FROM SPELEOTHEM δ18O AND GROWTH RATE TIME SERIES
Kevin J. Meyer, B.S.
University of Texas at Austin, December, 2011
Supervisor: Jay L. Banner
61 pages, 38 references, 3 tables
A 30 ky growth rate and high-resolution δ18O time series from a central Texas (TX) speleothem provides new climate insights when integrated with recently published speleothem records from New Mexico (NM) and Arizona (AZ), and a foraminifera record from the Gulf of Mexico (GOM). This comparison enables a possible regional assessment of factors controlling temporal variations in rainfall amount and moisture sources in the southwestern U.S. The three speleothem locations (TX, NM, AZ) span near 1,200 km. A regional east-to-west decrease in speleothem δ18O values of up to 7‰ is observed between TX and AZ. This is the same direction of regional decrease as in modern rainfall. This suggests 1) mixing of moisture from two sources, Pacific moisture (low δ18O), and GOM moisture (high δ18O), and 2) that these two sources have contributed moisture to the region for most of the last 30 ky. Prior to 15 ka, relatively large magnitude, millennial-scale oscillations (up to ~3‰) occur in the NM δ18O record while the TX and AZ records show smaller variations (~1‰). Starting at about 15 ka, both the AZ and NM records show a rapid increase in δ18O, whereas TX shows a decrease. This dip in the TX δ18O record corresponds with a δ18O decrease in the GOM seawater record that has been attributed to melt water influx. TX and NM show peaks in growth rate between about 15 and 13 ka whereas AZ shows a peak between 13 and 11.5 ka. All three speleothem records show significant decreases in growth rate in the Holocene. The speleothem δ18O time series appear to reflect changes in rainfall amount and composition. The correspondence of the TX and GOM records indicates GOM moisture composition as the major control on Late Pleistocene to Holocene TX precipitation composition. NM and AZ, by contrast, apparently received varying proportions of Pacific and GOM sources over this time period. Periods of high δ18O values in the NM and AZ records, when combined with relative high growth rates, may suggest increased overall water availability and GOM moisture contribution. The growth rate records are consistent with a regional transition to a drier climate from the latest Pleistocene to the Holocene.
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DEPOSITIONAL AND DIAGENETIC PROCESSES IN THE FORMATION OF THE EOCENE JACKSON GROUP BENTONITES, GONZALES COUNTY, TEXAS
Michael Nicholas Michaelides, MS Geology
University of Texas at Austin, December 2011
Supervisor: J. Richard Kyle
173 pages, 155 references, 20 tables
Bentonite clays are exposed in Paleogene strata stretching over 650 km parallel to the Texas coastline. This study focuses on a white and blue and a yellow and brown commercial Ca-montmorillonite bentonite near the city of Gonzales, Gonzales county, Texas. The deposits have stratigraphic ages of Late Eocene (~36.7 - 32.7 Ma). The bentonites in these deposits have varying colors, purities and brightness affording them diverse industrial uses. The distribution and geologic character of the high purity white and blue bentonite suggests that the deposit represents an accumulation of volcanic ash in a secondary tidal channel during the ash-fall event. A low rate of terrigenous clastic sedimentation and rapid accumulation of fresh ash were critical to the formation of high purity clay. The lower purity yellow and brown bentonites appear to have a fluvial origin marked by higher rates of detrital sedimentation and episodic accumulation of clay and ash.
The bentonite and associated strata were studied using optical microscopy, SEM, XRD and REE analyses to constrain their textural, mineralogic, and chemical character. Eocene pyroclastic volcanism is well documented from sources in southwestern North America, specifically in the Sierra Madre Occidental (Mexico), Trans-Pecos (Texas) and Mogollan-Datil (New Mexico) volcanic fields. Projected Eocene wind patterns support this region as a potential source for the Gonzales bentonites. A comparison of the trace and REE fingerprints of the white and blue bentonites and the yellow and brown bentonites with data available for Late Eocene volcanics in the North American Volcanic Database provides a couple of potential matches. The strongest potential match for the Late Eocene bentonite protolith is described as a sample of silicic tuff with an age range of 32.2 - 30.6 Ma, located in the southern Mexican state of Oaxaca. While the trace and REE match is strong, the tuff is somewhat young compared to the Jackson Group sediments. In addition, the sample location is due almost directly south of the Gonzales deposits, rather than the western location expected for a Gonzales bentonite source. The other potential matches are located in New Mexico, and the Mexican state of Chihuahua. These potential matches only have 6 REE available for comparison, and require further investigation. Many Paleogene volcanic units in southern North America are undocumented with regard to REE data or precise absolute ages. As additional geochemical analyses become available for a more extensive suite of Paleogene volcanic units, stronger matches with Gulf of Mexico Basin bentonites are expected to emerge.
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IMPACT OF TRACE METAL CONCENTRATIONS ON THE LUMINESCENCE OF HYDROTHERMAL CALCITE VEINS FROM THE BATOPILAS MINING DISTRICT, CHIHUAHUA, MEXICO
Stephanie Mills, B.S.
University of Texas at Austin, May 2009
Supervisor: J. Richard Kyle
77 pages, 33 references
This project investigates the effect of trace-metal concentrations on the photoluminescence (PL) and cathodoluminescence (CL) of hydrothermal calcite from the Batopilas mining district as a contribution to understanding vein paragenesis and constraining hydrothermal fluid chemistry.
The calcite veins studied exhibit PL colors ranging from red-violet to pink to orange when exposed to short wave UV (254 nm). The change in color is coupled with an increase in PL intensity, so that the red-violet PL color is the weakest intensity and the orange PL is the strongest. Metallic minerals present include native silver, galena, and sphalerite.
The bulk of the calcite veins bearing metallic minerals fall into the pink category. This supports the observation that Pb, Zn and Ag sulfides and native Ag occur in calcite veins exhibiting pink PL. Since the pink PL coincides with samples containing only Pb and Zn sulfides, it does not appear at this time that the relationship can be applied to exclusively silver-bearing veins.
Trace-element studies show Mn concentration increases from 1,000 ppm to 10,000 ppm and Ce from 10 ppm to 100 ppm with color and intensity variation. The other trace-elements show no pattern. These data lead to the conclusion that Mn, the main luminescence activator for calcite, and Ce, a sensitizer, are the main controls on PL color and intensity.
Studies on the CL emission spectra show all samples with a peak close to 600 nm, but variations in intensity from 500 counts to 1,800 counts between samples. Trace-element data suggest that an increase in Zn concentration from 2 to 10 ppm is the cause of CL intensity variation.
CL microstratigraphy in one sample was analyzed, and preliminary data indicate a relationship between the zonations and Mn, Fe, and Ce. These relationships are general at best and require more precise measurements to be interpreted decisively; however the apparent influence of an activator, quencher, and sensitizer on the same microstratigraphy is compelling.
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DISTRIBUTION AND DEVELOPMENT OF MIDDLE MIOCENE SUBMARINE FANS, TARANAKI BASIN, NEW ZEALAND
Renas Ismael Mohammed, MS. GeoSci.
University of Texas at Austin, August 2011
Supervisor: William L. Fisher
83 pages, 41 references
The Taranaki Basin was formed as a consequence of multiple geologic events. From the Cretaceous period until present, it went through rifted margin, passive margin, foreland basin, and back-arc phases. A dominantly sandy unit, the Moki Formation, was deposited during the Middle Miocene within the Taranaki Basin offshore the west coast of the North Island of New Zealand. The study area covers about 1600 km2 of the southern part of the north Taranaki graben, an area covered by a 3D seismic volume. The Moki Formation is interpreted as a basin floor fan deposit that accumulated during basinward migration of the shelf edge with supplied sediments sourced from the SSE.
Seismic profiles revealed that the mound-shape reflectors of Moki fan deposits situated between continuous reflectors of underlying Oligocene carbonates and hemipelagic muds of the overlying Manganui Formation. The reflections of the Moki sandy fan deposits locally grade laterally into interlobal deposits of hemipelagic muds. Correlation between wells Witiora-1, Taimana-1, and Arawa-1 verified the seismic interpretation, which shows an overall thickness variation of fan deposits that range from a greater thickness in the middle part of the sand lobe accumulation towards diminished thicknesses on the flanks. Gamma ray facies show clear progradation then aggradation motif that confirm the results from the seismic analyses. Depending on seismic attribute maps, paleochannels associated with the sand bodies sharing a SE to NW flow direction can be distinguished. Due to the volcanic activity in the eastern mobile belt, no paleochannels or significant stratigraphic features were recognized within the studied interval of the seismic data. Generally, in the study area, the fan deposits represent sand rich deposits that developed and prograded from south to north with variations in lateral extent driven by three major shifts in sediment pathways as the feeder channel orientations changed.
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PALEOGENE SEDIMENTATION PATTERNS AND BASIN EVOLUTION DURING ANDEAN OROGENESIS, MIDDLE MAGDALENA VALLEY BASIN, COLOMBIA
Christopher John Moreno, M.S.Geo.Sci
University of Texas at Austin, August 2010
Supervisor: Brian K. Horton
49 pages, 55 references, 4 tables
The Central Cordillera and Eastern Cordillera of the northern Andes form the western and eastern flanks of the north-trending Middle Magdalena Valley basin. Previous estimates for the timing of initial exhumation of the two cordilleras range from ~100 to ~10 Ma. Accurately constraining the spatial and temporal distribution of deformation in Colombia has implications for the shortening history of the Andean convergent margin and the prediction of rapid lateral facies changes in sedimentary basins in close proximity to sediment sources.
This study applies sandstone petrographic point counts, field sedimentological analyses of basin fill, and paleocurrent measurements of trough cross-stratification, clast imbrication, and flute casts to provide new insights into the tectonic history of the flanks of the Middle Magdalena Valley basin. Between the lower and upper Paleocene strata of the Lisama Formation, paleocurrent orientations show a shift from northward to eastward transport. This change in sediment dispersal coincides with a shift from a cratonic (Amazonian) to orogenic (Andean) sediment source, as recorded by published U-Pb detrital zircon geochronological results (Nie et al. 2010), suggesting initial uplift of the Central Cordillera by mid-Paleocene time. Later in the basin's history, establishment of an alluvial-plain system with meandering-channel deposits is recorded in lower–middle Eocene strata of the lower La Paz Formation.
Consistent eastward paleocurrents characterize mid-Paleocene through uppermost Eocene strata, indicating a continuous influence of western sediment source areas. However, within the upper middle Eocene succession (~40 Ma), at the boundary between the lower and upper La Paz Formation, sandstone compositions show a dramatic decrease in lithic content. This compositional change is accompanied by a facies shift to amalgamated fluvial channels, reflecting changes in both the composition and proximity of the western sediment source. We attribute these changes to the growing influence of the exhumed La Cira/Infantas paleohighs off the western flank of the present-day Nuevo Mundo syncline.
In the uppermost Eocene strata of the Esmeraldas Formation, paleocurrents show a switch to dominantly westward transport that persisted through the Neogene. In addition, deposits show a contemporaneous decrease in the amount of coarse-grained channel deposits. These changes are interpreted to reflect the onset of exhumation in the Eastern Cordillera. The lack of a significant change in sandstone compositions at this boundary suggests a compositional similarity between strata uplifted by the Lisama structure and the Eastern Cordillera. These data support and further refine previous thermochronologic and provenance studies which suggest that uplift-induced exhumation of the Central Cordillera and Eastern Cordillera commenced by mid-Paleocene and late Eocene-early Miocene time, respectively.
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FRACTURE APERTURE AND SPACING PATTERNS IN TWO FOLDED QUARTZ ARENITES : CAMBRIAN FLATHEAD FORMATION, TETON RANGE, WYOMING AND CAMBRIAN ERIBOLL FORMATION, NORTHWEST SCOTLAND
Frank L. Morgan, Bachelor of Science in Geological Sciences
University of Texas at Austin, May 2011
Supervisors: Stephen E. Laubach and Mark Cloos
59 pages, 37 references, 4 tables
Understanding the controls on opening-mode fracture width, or kinematic aperture, in folds can help improve predictions of fluid flow and storage. However, it is challenging to sample subsurface fractures that have widths large enough to preserve porosity and affect fluid flow. Microfracture data can be analyzed to help understand fracture patterns in the subsurface. Fracture patterns within two folds, an open syncline in the Flathead Formation, Teton Range Wyoming and the limb of a gentle anticline in the Eriboll Formation, NW Scotland were investigated and described using their fracture intensities, the number of fractures per unit length along a scan line. Fracture kinematic aperture was measured along lines of observation in outcrop and in thin-section along with spacing between fractures. Fracture width distribution can be described using a power law, which shows that strain is manifested in large fractures rather than microfractures. Fracture widths range from 5.10×l0-4 mm to 1.34 mm and are described by power laws spanning up to three orders of magnitude. Both the Flathead and the Eriboll Formation displayed proportionally more large fractures and fewer small fractures than was expected. Strain was greatest at the hinge of the fold in the Flathead Formation, but showed an opposite effect in the Eriboll Formation due to fractures being caused by an unknown structure or because fractures are unrelated to folding in the region.
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QUANTITATIVE SEISMIC GEOMORPHOLOGY OF A CONFINED CHANNEL COMPLEX, SOUTHERN ATWATER FOLD BELT, GULF OF MEXICO, U.S.A.
Jessica Leanne Morgan, M.S.
University of Texas at Austin, August 2010
Supervisor: Lesli J. Woo
76 pages, 40 references, 2 tables
The structures along the Atwater Fold belt form important deep-water hydrocarbon traps in the northern Gulf of Mexico. The purpose of this study is to map and quantify the morphology, sedimentology and architecture of Plio-Pleistocene basin floor fan systems outboard of the Poseidon Minibasin, located along the Atwater deep-water fold belt (mid-Miocene to Pliocene), and apply that information to determine the temporal and spatial nature of the fill and its implications as a reservoir analog. The data set includes ~2200 km sq. of 3D seismic data, along with information from several wells. Wireline logs show the Tertiary age deposits outboard of the Sigsbee Escarpment to be several hundred feet thick, sharp-based, dominantly coarse-grained (sandy) but fining up cycles composed of sandy basin floor fans, mass transport complexes and leveed channels developed in a confined setting within deep-water "valleys."
The largest valley formed in five main stages: initiating from narrow channel incision, widening through lateral incision and sidewall slumping, straightening, and finally flooding and infilling. The valley system is ~20,000 feet across and ~ 1,400 feet deep, with what look like well-developed levees ranging from 700 to 1300 feet at their thickest point extending ~19000 feet away from the channel. This system is underlain by a ~700 foot thick mass transport complex and overlain by younger, low sinuosity leveed channel systems. Both of these systems appear to have been sourced by large submarine drainages, originating from a shelf edge sediment source system to feed the rugose slope with deep-water channel pathways uninhibited by salt wall inflation at the time of valley deposition.
Major phases of salt thrusting along the southern edge of the Atwater were contemporaneous with the formation of these large, through-going valley system, which appear to be associated with the period of sheet thickening and development of monoclinal basinward dip related to rafted mini-basin docking.
Well log signatures show evidence for armored clay drapes along the valley margins as well as a flattening of lateral accretion packages toward the distal end of the system. The flattening of these packages seems to signal proximity to the fan terminus, which would serve as an important indicator of spatial extent of plays in deep-water.
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CONTROLS ON AND USES OF HYDROCHEMICAL AND ISOTOPIC HETEROGENEITY IN THE PLATEAU AQUIFER SYSTEM, CONTIGUOUS AQUIFERS, AND ASSOCIATED SURFACE WATER, EDWARDS PLATEAU REGION, TEXAS
Hardie Seay Nance III, Ph.D.
University of Texas at Austin, May 2010
Supervisors: John M. Sharp and Jay L. Banner
300 pages, 136 references, 2 tables
Groundwater and surface water in the Edwards Plateau region exhibits spatial variability arising from mineral differences in aquifers and mixing of groundwaters with diverse flow paths and ages. Integration of basic hydrochemical and isotope data (87Sr/86Sr, δ18O, δD, 14C, 3H) document that groundwaters in the Lower Cretaceous Edwards-Trinity (Plateau) aquifer system reflect intermixing of modern and Pleistocene recharge. Pleistocene recharge occurred under cooler paleo-climatic conditions, based on δ18O variance of 4.59‰, and flow traversed sub-cropping Permian evaporite and Triassic strata under hydraulic conditions that promoted upward flow into the Plateau system. Recharge areas may have been in topographically elevated areas in New Mexico that no longer are connected with the Plateau. Present distribution of groundwaters with higher SO4/Cl values occurring beneath topographic divides on the Plateau suggests that modern recharge occurs preferentially in losing-stream networks and is inhibited on divides by low-permeability soils.
Relationships between 14C, tritium, δ13C, and Mg/Ca values confirm that effectively younger groundwaters occur beneath the upper parts of drainage networks, but down slope of divides. Thus, groundwater-age and hydrochemical data suggest that recharge preferentially occurs in the upper parts of drainage networks. Correlations between groundwater relative age and Mg/Ca enable estimation of the proportion of modern recharge at specific well locations based on Mg/Ca values and enables estimating local absolute recharge rates from regional-scale recharge estimates obtained from regional flow models.
The Upper Colorado River bounds the northern and northeastern margin of the Plateau system and shows systematic chemical evolution along its flow path, including decreasing salinity and increasing SO4/Cl values. The stream can be conceptually divided into three segments that each reflect groundwater inputs from five hydrochemically distinct intervals: 1) deep Permian and Pennsylvanian reservoirs similar to those that produce hydrocarbons in the region; 2) Upper Permian halite (Salado Formation); 3) the Triassic siliciclastic aquifer (Dockum Group); 4) the sulfate-evaporite-bearing Permian system (Ochoan, Guadalupian, and Leonardian Series); and 5) the Plateau aquifer system. Conservative mixing models suggest that any aquifer that the river is traversing at a specific location contributes a distinct hydrochemical signature, but the dominant contribution is from the Plateau system.
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DEPOSITION OF THE FLUVIAL ERICSON SANDSTONE, ROCK SPRINGS UPLIFT, SW WYOMING: HOW EMBRYONIC LARAMIDE UPLIFT CONTROLLED SEDIMENTATION
Andrew Nicholson, B.S.
University of Texas at Austin, May 2010
Supervisor: Ronald Steel
30 pages, 9 references
The Ericson Sandstone is a Campanian fluvio-estuarine sandstone and has been re-examined on and around the Rock Springs Uplift in SW Wyoming. The latter is a Laramide feature, usually believed to have been uplifted in latest Cretaceous and Paleogene times. It is proposed, based on Ericson thickness changes and the occurrence of multiple internal erosion surfaces, or internal unconformities, around the Rock Springs Uplift that the broader area was repeatedly active during the deposition of the Trail and Rusty members of Ericson Formation, possibly as old as 79my (early Middle Campanian). This is justified by gross interval isopach maps of the Trail and Rusty members that show a pronounced area of decreased accommodation (thinner sediment accumulation) across the crest of the uplift, the presence of unconformities at the base of Trail and top of Rusty members, and increased internal erosion surface density (# of surfaces per vertical measured section divided by the gross thickness) trends within the Trail and Canyon Creek members from flank to crest. However, the unconformities have a much more widespread distribution than the uplift itself and are likely to be partly caused by significant basinward shifts of alluvial plain deposition, possibly forced by large-scale isostatic uplift of the Sevier fold-and-thrust belt at these times. The uplift activity during Ericson deposition was primarily in the form of reduced rates of subsidence around the uplift rather than positive landscale relief as there is no evidence of stratal onlap from flank to crest, only systematic thinning
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SEDIMENT TRANSPORT DYNAMICS IN THE LOWER MISSISSIPPI RIVER: NON-UNIFORM FLOW AND ITS EFFECTS ON RIVER-CHANNEL MORPHOLOGY
Jeffrey Albert Nittrouer, Ph. D.
University of Texas at Austin, December 2010
Supervisor: David Mohrig
158 pages, 78 references, 10 tables
This dissertation examines the dynamics of sediment transport and channel morphology in the lower Mississippi River. The area of research includes the portion of the river where reach-averaged downstream flow velocity responds to the boundary condition imposed by the relatively uniform water-surface elevation of the receiving basin. Observational studies provided data that are used to identify channel-bed sediment composition, and measure bed-material sediment flux and the properties of the fluid-flow field over a variety of water-discharge conditions. The analyses demonstrate that a significant portion of the channel bed of the final 165 kilometers of the Mississippi River consists of exposed and eroding underlying relict sedimentary strata that qualify as surrogate bedrock. The exposed bedrock is confined to the channel thalweg, particularly in river-bend segments, and actively mobile bed-material sediments are positioned on subaqueous bars fixed by river planform. The analyses for sediment flux provides insight to the nature of sediment transport: during low- and moderate-water discharge, bed-material movement occurs primarily as minimal bedform flux, and so bed materials are not transferred between alluvial bars. During high-water discharge, bed-material transport increases one-hundred fold, and sands move as a part of both suspended and bedform transport. Physical models are used to show that skin-friction shear stress increases by a factor of ten for the measured water-discharge range. This change is not possible given conditions of uniform water flow, and therefore non-uniform flow in response to the Mississippi River approaching its outlet has a significant impact on the timing and magnitude of sediment flux through the lower river. In order to estimate the dynamics of bed material movement from the uniform to non-uniform segment of the river (lower 800 km), data for channel morphology are used to construct a model that predicts spatial changes in water-flow velocity and bed-material flux over a range of water-discharge conditions. The model demonstrates that non-uniform flow tends to produce a region of net channel-bed aggradation between 200-700 kilometers above the outlet, and a region of channel-bed degradation for the final 200. The implication for these results for the spatial variability of channel morphology and kinematics is explored.
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INTRA-MEANDER GROUNDWATER-SURFACE WATER INTERACTIONS IN A LOSING EXPERIMENTAL STREAM
John David Nowinski, MSGeoSci
University of Texas at Austin, August 2010
Supervisor: Meinhard Bayani Cardenas
80 pages, 52 references
Groundwater-surface water interactions between streams and shallow alluvial aquifers can significantly affect their thermal and chemical regimes and thus are critical for effective management of water resources and riparian ecosystems. Of particular significance is the hyporheic zone, an area delineated by subsurface flow paths that begin and end in surface water bodies. Although detailed work has examined hyporheic flow in the vertical dimension, some studies have suggested that the drop in a stream's elevation as it flows downstream can laterally extend the hyporheic zone. This study examines intra-meander hyporheic flow using extensive field measurements in a full-scale experimental stream-aquifer system. Synoptic head measurements from 2008 and 2009 and a lithium tracer test were conducted to determine the extent and nature of hyporheic flow within the meander. Permeability was measured and sediment cores were analyzed from 2008 to 2009 to assess aquifer properties. Finally, transient head and temperature measurements were collected during flooding events to assess the sensitivity of intra-meander hyporheic flow and temperature to stream discharge. Results verify that hyporheic flow through meanders occurs, but show that it is sensitive to whether a stream is gaining or losing water to the subsurface overall. In addition, permeability and core grain size results indicate moderate heterogeneity in permeability can occur in aquifers composed of relatively uniform sediment. Results also demonstrate that permeability in alluvial aquifers can evolve through time. Such evolution may be driven by groundwater flow, which transports fine particles from areas where porosity and permeability are relatively high and deposits them where they are relatively low, thus creating a positive feedback loop. Finally, measurements during flooding indicate that steady-state hyporheic flow and the thermal regime within the aquifer are largely insensitive to stream discharge. Together, these results expand upon previous field studies of intra-meander hyporheic flow and verify previous modeling work, although they demonstrate a level of complexity within these systems that should be considered in future work.
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THE EVOLUTION OF SKELETAL DEVELOPMENT IN EARLY TETRAPODS: ANATOMY AND ONTOGENY OF MICROSAURS (LEPOSPONDYLI)
Jennifer Catherine Olori, Ph.D.
University of Texas at Austin, May 2011
Supervisor: Christopher J. Bell
518 pages, 217 references, 37 tables
Because the ancestry of extant amphibians remains highly controversial, under traditional perspectives, amphibians and amniotes often are distinguished by differences in developmental mode rather than their evolutionary relationships. Resolution of relationships is important, however, because phylogeny affects interpretations of biology, including the evolution of development. To address those issues, I documented the growth and development of two extinct lepospondyls, Microbrachis pelikani and Hyloplesion longicostatum, and compared the patterns in those taxa to data from other tetrapods. I quantified allometry in the skeleton using both measurement-based and geometric morphometric analyses. I applied Ontogenetic Sequence Analysis (OSA), a size-independent method, to the reconstruction of ossification sequences based on fossils. I also documented skeletal morphogenesis and used Parsimov Analysis and Parsimov-based Genetic Inference of ossification sequence data to evaluate the three hypotheses of extant amphibian ancestry, the Lepospondyl (LH), Temnospondyl (TH), and Polyphyletic (PH) hypotheses.
Skeletal growth in Microbrachis pelikani and Hyloplesion longicostatum is primarily isometric. Comparisons with data from other Paleozoic taxa suggest that isometry was the ancestral pattern of growth in tetrapods. All regression analyses had a linear fit indicating lack of an abrupt metamorphosis. Absence of metamorphosis is also supported by the possession of lateral lines in both taxa throughout ontogeny, and Microbrachis pelikani additionally retained gills. However, ossification of the skeleton was completed at small body size. The greatest resolution in ossification sequence reconstruction was achieved with OSA, but results from all reconstruction methods indicated advanced ossification of the pubis and delayed ossification of the scapula in the lepospondyls. In terms of total number of sequence shifts optimized across each hypothesis of amphibian relationships, the TH had the shortest tree length. However, the values for the three hypotheses did not differ significantly, demonstrating that none was supported strongly.
Based on my synthesis of new developmental data, I propose that Microbrachis pelikani and Hyloplesion longicostatum expressed a mosaic pattern of skeletal development. That pattern included a gradual transition to an adult morphology, and a lack of an amphibian-like metamorphosis. A similar pattern is common to most early tetrapods and Eusthenopteron, supporting the hypothesis that metamorphosis is not ancestral for Tetrapoda.
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CREATION AND DEGRADATION OF AN AQUIFER CAUSED BY LAND USE CHANGE: SEYMOUR AQUIFER, ROLLING PLAINS, TEXAS
Jeffrey Jack Olyphant, M.S.Geo.Sci.
University of Texas at Austin, December 2009
Supervisor: Bridget R. Scanlon
96 pages, 79 references, 13 tables
Land-use change can greatly impact water resources, both water quantity and water quality, by changing the partitioning of water at the land surface among evapotranspiration, runoff, and recharge. The objective of this study was to evaluate the impact of land-use change on water resources in a semiarid region using the Seymour aquifer in the Rolling Plains of Texas as an example. Historical reports indicate that the aquifer was mostly created as a result of land-use change and nitrate contamination has been recorded since the 1940’s. Unsaturated zone profiles (18) drilled under three land-use settings (1 rangeland, 11 rain-fed and 6 irrigated) were used to quantify impacts of land-use on groundwater recharge and subsoil nitrate reservoirs, and to link land surface source data with nitrate levels in the aquifer. It is very difficult to find a site that represents the natural rangeland system because most of the region has been cultivated. Only one profile approximates the natural rangeland ecosystem and it has minimal recharge (6 mm/yr), a moderate chloride inventory (358 kg/ha), and a low nitrate inventory (5 kg/ha N). Rain-fed agriculture has moderate recharge (median: 24 mm/yr) and low to moderate inventories of chloride (median: 123 kg/ha) and nitrate (median: 33 kg/ha NO3-N). Irrigated agriculture has moderate to high recharge rates (median: 70 mm/yr), moderate to high chloride inventories (median: 590 kg/ha), and high nitrate inventories (median: 253 kg/ha). Replacement of natural rangeland ecosystems with rain-fed agroecosystems increased recharge indicating that cultivation induced the median water table rise of 8 m recorded from 1910 to 1934, essentially creating the aquifer. The implementation of irrigation in the region began in the 1950’s, tripling the recharge under the irrigated systems. Long-term groundwater hydrographs have remained stable suggesting that current pumpage is balanced by the increased recharge under rain-fed and irrigated agriculture and is sustainable.
Many of the profiles under rain-fed agriculture (9 of 11) indicate that increased recharge from cultivation has already flushed accumulated salts and nutrients into the underlying aquifer. One profile shows a displaced nitrate inventory of 272 kg/ha NO3-N that should correspond to initial cultivation based on chloride soil water age dating. This nitrate may be attributed to mineralization and nitrification of soil organic nitrogen during initial cultivation related to increased soil moisture and soil aeration. Mobilization of an inventory of this size to the underlying aquifer would produce an increase in groundwater nitrate concentrations of 12.4 mg/L NO3-N based on a current saturated thickness of 7 m (median 1997) and could explain the elevated nitrate concentrations found throughout the aquifer prior to intensive use of synthetic fertilizers. Inventories under cultivated land (86% rain-fed, 14% irrigated by area) indicate that there is sufficient nitrate in the unsaturated zone to maintain current nitrate levels in the aquifer (median: 15.3 mg/L NO3-N), potentially increasing groundwater concentrations by 2.8 mg/L, with 56% derived from irrigated land. Evaluations of surface inputs indicate that irrigated agriculture represents ~ 74% of the total excess nitrogen in the cultivated system and that fertilizer is the dominant source. Current management strategies in irrigated systems do not take into account nitrate inputs from irrigation water, which alone are sufficient to meet crop nitrogen demands, resulting in a 100% mean annual over application of fertilizer. Best management strategies incorporating nitrate in irrigation water should reduce groundwater nitrate contamination and production costs by mining this free nitrate resource in irrigation water and eliminating unnecessary use of fertilizer. Understanding impacts of land-use change is essential for effective management of sustainable groundwater resources in these semiarid regions.
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ECONOMETRIC ANALYSIS OF THE IMPACT OF MARKET CONCENTRATION ON PRICES IN THE OFFSHORE DRILLING RIG MARKET
Amanda Chiderah Onwuka, MA
University of Texas at Austin, December 2010
Supervisor: Christopher Jablonowski
53 pages, 22 references, 26 tables
This thesis presents an econometric methodology for analyzing the impact of market concentration (HHI) on the day rate prices paid by E&P operators for the lease of drilling rigs. It is an extension of the work of Lee (2008), 'Measuring the Impact of Concentration in the Drilling Rig Market'. Specifically, the work entailed using a more detailed time series data than was initially used (quarterly), analyzing impact of concentration on day rate prices by water depth specification of drilling rigs, and accounting for the impact of autocorrelation on the analysis. The results for jack-ups, without adjustment for autocorrelation, supported the results of the prior study i.e. showing that increase in HHI causes rig day rate price increase. However, the results for semi-submersibles was inconclusive as it varied from region to region and also was contrary to the assumptions of positive relationships between HHI and day rate prices made in this study. These results imply that market concentration caused both price increase and decrease within the industry depending on whether it increased market power or increased cost efficiency and technological ability.
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FACIES AND DEPOSITIONAL HISTORY OF APTIAN (CRETACEOUS) BEACHES: A 120 MY OLD RECORD OF FETCH AND PREVAILING WIND PATTERNS DURING TRANSGRESSION OF THE TEXAS HILL COUNTRY
Leigh A. Owens, B.S.
University of Texas at Austin, May 2009
Supervisor: Charles Kerans
61 pages, 16 references, 1 plate
Carbonate beach complexes are significant in that they are characteristically excellent shoreline indicators. These deposits are unique because of how rarely they get preserved in the rock record. The Cow Creek Formation of Central Texas provides one of the best exposed examples of a carbonate beach complex found in the Phanerozoic sedimentary record. It is Aptian (Cretaceous) in age and is a tectonically undisturbed outcrop that preserves a range of shallow marine depositional environments. Lower Cretaceous strata of Central Texas include, in ascending order, the Hammett Shale, the Cow Creek Limestone, and the Hensel Sandstone. They represent a sedimentary sequence deposited during one marine transgression and regression.
This study utilizes the Cow Creek foreshore-upper shoreface exposure to map and document the sedimentary facies. A detailed analysis of grain size, sedimentary structures, and major allochems, has been used to identity five facies in the Cow Creek outcrop. The widths and lateral extents of these facies have been used to constrain the likely water-depth range of the receiving basin during the Aptian. The dip angle of the foreshore and the facies architecture of the upper shoreface have been used to estimate the wave fetch, wave height and the prevailing wind direction. An ideal profile for the ancient prograding beach complex was constructed using outcrop data. This study details the depositional history of the Cow Creek Formation in the greenhouse climatic conditions of the Lower Cretaceous and establishes a microtidal, wind-dominated, foreshore-shoreface environment.
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STRUCTURAL DIAGENETIC ATTRIBUTES OF THE LATE WILLIAMS FORK SANDSTONES WITH IMPLICATIONS FOR PETROPHYSICAL INTERPRETATION AND FRACTURE PREDICTION, PICEANCE BASIN, COLORADO
Aysen Ozkan, Ph.D.
University of Texas at Austin, May 2010
Supervisors: Kitty L. Milliken and Steve E. Laubach
304 pages, 228 references, 16 tables
Diagenetic and structural aspects of tight gas sandstones must be addressed concurrently in order to fully understand low-permeability sandstones and to better predict their reservoir quality attributes that arise from a combination of pore-scale and fracture distribution characteristics. This dissertation focuses on aspects of rock evolution that are germane to concurrent structural and diagenetic evolution, such as loading and thermal history, rock mechanical property evolution, and fracture timing. I tested the hypothesis that the cement precipitation step, governed by thermal exposure and grain surface attributes, governs how sandstone attributes evolve using observations from the Late Cretaceous Williams Fork sandstones from the Piceance Basin, Colorado.
My research shows that essential information for predicting and understanding fracture patterns in sandstone can be obtained by unraveling cement precipitation (diagenetic) history. Fractures depend on the mechanical properties existing during fracture growth. I show that key rock mechanical properties (subcritical crack index, Young`s modulus and Poisson`s ratio), petrophysical behavior, and reservoir quality depend in a systematic way on time-temperature history and the intrinsic grain surface attributes of these sandstones.
I classified the Williams Fork lithofacies petrographically and correlated those with log responses to create a model that can be used to predict reservoir quality and diagenesis directly from well logs. I determined rock mechanical characteristics by measuring the subcritical crack index (SCI), a mechanical property that influences fracture distribution characteristics, and by examining log-derived bulk mechanical properties. To quantify the influence of quartz cementation on the SCI and to determine the range of SCI values for sandstone of given framework composition at different diagenetic stages, I measured SCI on Williams Fork core samples and their outcrop equivalents. Diagenetic modeling is applied to determine the sandstone characteristics during fracturing.
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NEW METHODS FOR QUANTIFYING AND MODELING ESTIMATES OF ANTHROPOGENIC AND NATURAL RECHARGE : A CASE STUDY FOR THE BARTON SPRINGS SEGMENT OF THE EDWARDS AQUIFER, AUSTIN, TEXAS
Michael Charles Passarello, M.S. Geo. Sci.
University of Texas at Austin, May 2011
Supervisors: John M. Sharp Jr. and Suzanne A. Pierce
185 pages, 104 references, 14 tables
Increased population and recent droughts in 1996 and 2009 for the Barton Springs segment of the Edwards Aquifer have focused attention on groundwater resources and sustainability of spring flow. These springs serve as a local iconic cultural center as well as the natural habitat for the endangered Barton Springs salamander. In response to the potential compromise of these vulnerable groundwater resources, a two-dimensional, numerical groundwater-flow model was developed for the Barton Springs / Edwards Aquifer Conservation District and other governmental entities to aid in aquifer management. The objective of this study is to develop new methods of quantifying and distributing recharge for this model. The motivation for conducting this study includes the following: recent availability of more extensive data sets, new conceptual models of the aquifer system, and the desire to incorporate estimates of urban recharge. Estimates of recharge quantities and distributions for natural and artificial sources were implemented within this model to simulate discharge at Barton Springs and water-level elevations from January, 1999 to December, 2009. Results indicate that the new methods employed generated good agreement amongst simulated and observed discharge and water-level elevations (Root mean square error of 0.5 m3 sec-1 and 10.5 m, respectively). Additionally, these recharge calculations are decoupled from Barton Springs discharge which eliminates the circular logic inherent with the previous methodology. Anthropogenic, or artificial, recharge accounts for 4% of the total recharge between January, 1999 and December, 2009. Using observed data to quantify contributions from leaky utility lines and irrigation return flows, recharge estimates were completed with spatial and temporal resolution. Analyses revealed that on a month by month basis, anthropogenic contributions can vary from ‹1 to 59% of the total recharge. During peak anthropogenic recharge intervals, irrigation return flow is the most significant contributor. However, leakage from utility lines provides more total recharge during the study period. Recharge contributions from artificial sources are comparable to the mid-size watershed contributions over the ten-year analysis period. Urban recharge can be a critical source for buffering seasonal fluctuations, particularly during low flow periods. Outcomes are relevant for habitat conservation, drought response planning, and urban groundwater management.
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ALBIAN/MAASTRICHTIAN TECTONO-STRATIGRAPHIC EVOLUTION OF CENTRAL SANTOS BASIN, OFFSHORE BRAZIL
Mônica Alves Pequeno, Ph.D
University of Texas at Austin, December 2009
Supervisor: William Fisher
Co-supervisor: Martin Jackson
205 pages, 136 references
The dissertation examines the interaction between basement tectonics, salt tectonics and sedimentation during the Late Cretaceous basement reactivation in the center of the Santos Basin. The study area is a seismic volume 60 x 30 km2 in area, augmented by 2D regional seismic lines. The results of seismic interpretation and structural restorations revealed important inversions in the Late Cretaceous, including inversion of an NNE-oriented aborted rift segment known as Merluza Graben.
The following tectono-stratigraphic evolution was inferred. During the Albian, basin subsidence and differential loading by the overburden caused salt to flow basinwards. In the Late Turonian, intraplate compression resulted in uplift of the onshore and proximal areas of the Santos Basin and in a newly recognized basement inversion in deep water. ENE and NNE oriented structures were reactivated. The uplift exposed the Turonian shelf and a new shelf began to prograde. The first shelves were narrow (~25 km wide) but enlarged to 60 km in the Santonian. Salt influenced the position of the shelf break and the progradation pattern of the shelf margin. Because of the continuous accommodation space provided by salt withdrawal underneath the sedimentary wedge, the shelf margin aggraded until underlying salt welded, after which the shelf prograded to a position around 50 km to the east of the present-day shelf break. Deformation peaked in the Late Santonian when the shelf was widest, the rate of progradation of the shelf margin was anomalously high, and transtension along the borders of the Merluza Graben allowed Late Santonian magma to intrude. Salt acted as a partial seal, causing a large part of the magma to spread beneath it. Some magma formed sills inside the evaporitic layer, intruding zones of dilation in the salt. Magma also followed the top of the evaporitic layer and intruded salt-related faults as dikes. These dikes supplied sills in the overburden and extrusive flows emerged on the Late Santonian seafloor from ENE-striking transtensional zones. Right-lateral reactivation of the Merluza Graben borders slightly compressed the graben, which favored sill injection in Coniacian/Santonian strata. Tectonic activity diminished towards the end of the Cretaceous.
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FACIES ARCHITECTURE AND PETROLOGY OF AN ALBIAN RUDIST REEF MEDINA AREA, SOUTH TEXAS
Madelyn S. Percy, B.A.
University of Texas at Austin, May 2009
Supervisor: Charles Kerans
45 pages, 21 references
The purpose of this study is to better describe the characteristic facies of an Albian (Lower Cretaceous) caprinid rudist reef complex so as to understand the depositional history and associations between different energy-levels and faunal types in the Late Cretaceous seas around South Texas. This understanding was gained using mapping techniques, as well as the study of the rocks at the outcrop, slab, and thin section scales. A second goal of this project is to determine if geologists can predict subsurface geometry from boreholes, under the assumption that there is a link between rock fabric in hand sample scale and the bioherms' microfacies.
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AZIMUTHAL ANALYSIS OF HYBRID GATHERS
Anisa Marie Perez, M.S.Geo.Sci.
University of Texas at Austin, May 2009
Supervisor: Robert Tatham
89 pages, 14 references
The cross-spread formed by intersecting source and receiver lines, or “hybrid gather” consisting of all common mid-points (CMPs) in a reflection patch defined by the acquisition geometry, has been revived in recent years as a possible solution to the increasing need for ever-improving imaging of 3-D seismic reflection data. These hybrid gathers, however, are currently not widely used in processing. Development of processing procedures for hybrid gathers is needed to further the efficiency of their application. The use of hybrid gathers in processing is justified by their performance as an areal array in attenuating both random and coherent noise from all azimuthal directions. Hybrid gathers also allow for azimuthal filtering to correct for wave propagation effects. Through an azimuthal analysis in an azimuthally anisotropic medium, the effects of structural dip on reflection time can be isolated and separated from pre-stack propagation effects of the media, particularly distortions due to azimuthal anisotropy. A binning strategy is determined for hybrid gathers which best allows for azimuthal anisotropy to be observed and distinguished from structural dip. This allows for improved velocity estimation for imaging and separate analysis of azimuthal variations in propagation properties of subsurface media at an early stage in the processing sequence. The degree and orientation of the anisotropy can then be estimated using a semblance method.
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LATE MIOCENE SEDIMENTATION IN THE CENTRAL ANDEAN FORELAND BASIN, SOUTHERN BOLIVIA: CONSTRAINT FROM MAGNETOSTRATIGRAPHY
Nicholas David Perez, B.S. Department of Geological Sciences
University of Texas at Austin, December 2009
Supervisor: Brian Horton
56 pages, 50 references, 3 tables
Competing models for the construction of the central Andes suggest a contrasting importance of tectonic and climatic forces on foreland basin evolution. Presented here is the first and most detailed magnetostratigraphic analysis of sediment accumulation rates from the Chaco foreland basin in southern Bolivia. Precise constraints on the timing of deposition for ~1370 m of nonmarine basin fill from the Angosto del Pilcomayo section near the town of Villamontes in southern Bolivia indicate various phases of slow and rapid sediment accumulation. The onset of high accumulation rates (up to ~680 m/Myr) began at ~7.7 Ma, correlating temporally with the proposed onset of climate shifts in the central Andes (as determined by other workers), South American monsoonal activity, a global climate shift, and proposed rapid uplift of the central Andean plateau, potentially as a result of lithospheric removal. This detailed record of foreland basin accumulation should be useful in furthering the understanding of the relationship between climatic, tectonic and sedimentation processes operating in contractional orogenic systems.
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STRATIGRAPHIC IMPLICATIONS OF THE SPATIAL AND TEMPORAL VARIABILITY IN SEDIMENT TRANSPORT IN RIVERS, DELTAS, AND SHELF MARGINS
Andrew Lucas Petter, Ph.D.
University of Texas at Austin, May 2010
Supervisor: Ronald Steel
205 pages, 227 references, 9 tables
Sediment delivery to a basin exerts a first-order control over sedimentation, and therefore study of sedimentary rocks can reveal information about the nature of sediment delivery in the past. This dissertation examines several aspects of this problem using experimental, outcrop, and subsurface data. Flume experiments were undertaken to test the combined effects of autogenic alluvial aggradation and forced regression on the development of fluviodeltaic stratigraphy. Alluvial aggradation occurred in response to steady relative sea-level fall, and eventually consumed the entire sediment budget as the river lengthened in response to forced regression. The Campanian Lower Castlegate Sandstone (Utah) was studied as a potential ancient analog resulting from similar autogenic behaviors as observed in the experiments. Extensive measurement of grain-size distributions and paleo-flow depths from outcrop were utilized to explore downstream changes in paleo-hydraulics of the ancient fluvial systems in the Lower Castlegate in response to extensive alluvial aggradation and consequent loss of sediment from transport. An interesting finding was the stratigraphic signature of backwater hydraulic conditions in the distal reaches of the Lower Castlegate paleo-rivers. Finally, a simple and novel inversion scheme was developed for estimating paleo-sediment flux from ancient shelf-margin successions. An advantage of the methodology is that it allows for both spatial and temporal reconstruction of paleo-sediment flux patterns. The inversion scheme was applied to shelf-margin successions in the Washakie-Sand Wash Basin of Wyoming, the New Jersey Atlantic margin, the North Slope of Alaska, and the Zambezi margin of East Africa using published subsurface datasets. The Neogene passive margins within the studied datasets were found to consistently deposit around one-third of their total sediment budget on the shelf-margin topset, and bypass two-thirds of their budget beyond the shelf edge. The implications of this finding on the flux of terrestrial-derived particulate organic carbon (POC) from rivers to the ocean were explored, and a long-term average flux of POC to deepwater storage was estimated. The sediment-flux inversion scheme was also applied to derive input parameters for stratigraphic modeling of the Ebro margin. The modeling results indicate that the autostratigraphic behavior of the margin may have been previously underestimated.
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MORPHODYNAMICS AND GEOMETRY OF CHANNELS, TURBIDITES AND BEDFORMS
Aymeric-Pierre Bernard Peyret, Ph.D.
University of Texas at Austin, December 2011
Supervisor: David Mohrig
203 pages, 41 references, 11 tables
The evolution of landscapes and seascapes in time is the result of the constant interaction between flows and topography. Flows change topography, which in turn change the flow. This feedback causes evolution processes to be highly non-linear and complex. When full analytical derivations of the co-evolution of topography and flow are not possible without oversimplifications, as is the case in river bends, recent large topographical datasets and modern computers allow for correlations between horizontal (planview) and cross-sectional geometry of channels. Numerical analysis in the Mississippi and Trinity rivers indicate that the type of correlation between river radius of curvature and bankfull channel width depends on the migration behavior of the river. In other cases, channel topography may only have a second-order effect on its own evolution, as is the case for fully depositional turbidity currents, and the evolution of æolian field topography may only be a function of this topography. I show that in these situations, changes in topography may be decoupled from details of the flow field and modeled very easily with a good accuracy.
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PRE-INJECTION RESERVOIR EVALUATION AT DICKMAN FIELD, KANSAS
Son Dang Thai Phan, MS
University of Texas at Austin, August 2011
Supervisor: Mrinal K. Sen
82 pages, 37 references, 2 tables
I present results from quantitative evaluation of the capability of hosting and trapping CO2 of a carbonate brine reservoir from Dickman Field, Kansas. The analysis includes estimation of some reservoir parameters such as porosity and permeability of this formation using pre-stack seismic inversion followed by simulating flow of injected CO2 using a simple injection technique.
Liner et at (2009) carried out a feasibility study to seismically monitor CO2 sequestration at Dickman Field. Their approach is based on examining changes of seismic amplitudes at different production time intervals to show the effects of injected gas within the host formation. They employ Gassmann's fluid substitution model to calculate the required parameters for the seismic amplitude estimation. In contrast, I employ pre-stack seismic inversion to successfully estimate some important reservoir parameters (P- impedance, S- impedance and density), which can be related to the changes in subsurface rocks due to injected gas. These are then used to estimate reservoir porosity using multi-attribute analysis. The estimated porosity falls within a reported range of 8-25%, with an average of 19%. The permeability is obtained from porosity assuming a simple mathematical relationship between porosity and permeability and classifying the rocks into different classes by using Winland R35 rock classification method. I finally perform flow simulation for a simple injection technique that involves direct injection of CO2 gas into the target formation within a small region of Dickman Field. The simulator takes into account three trapping mechanisms: residual trapping, solubility trapping and mineral trapping. The flow simulation predicts unnoticeable changes in porosity and permeability values of the target formation. The injected gas is predicted to migrate upward quickly, while it migrates slowly in lateral directions. A large amount of gas is concentrated around the injection well bore. Thus my flow simulation results suggest low trapping capability of the original target formation unless a more advanced injection technique is employed. My results suggest further that a formation below our original target reservoir, with high and continuously distributed porosity, is perhaps a better candidate for CO2 storage.
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MIDDLE-HAUTERIVIAN TO LOWER-CAMPANIAN SEQUENCE STRATIGRAPHY AND STABLE ISOTOPE GEOCHEMISTRY OF THE COMANCHE PLATFORM, SOUTH TEXAS
Ryan Matthew Phelps, Ph.D.
University of Texas at Austin, May 2011
Supervisor: Charles Kerans
227 pages, 349 references, 1 table
Carbonate platforms contain a wealth of information regarding the changing biota, sea level, ocean-chemistry, and climate of the Cretaceous Period. The Comanche platform of the northern Gulf of Mexico represents a vast, long-lived carbonate system that extended from west Texas through the Florida panhandle. In central and south Texas, excellent outcrops and an extensive suite of subsurface data provide an opportunity to document the evolution of this system, from the shoreline to the shelf-margin and slope. This study examines the changing facies, platform morphologies, and shelf-margin architectures of the mixed carbonate-siliciclastic, middle-Hauterivian to lower-Campanian interval. Stratigraphic results are integrated with stable-isotope geochemistry to document the detrimental effects of oceanic anoxic events on the carbonate platform.
Seven second-order, transgressive-regressive supersequences of 3-14 Myr duration are defined in south Texas using sequence stratigraphic analysis of shelf-interior facies successions. Second-order supersequences are subdivided into several third-order depositional sequences of 1-3 Myr duration. In these sequences, facies proportions and stratal geometries of the shelf-interior are found to be the result of changing platform morphology and temporal evolution from distally-steepened ramp to rimmed-shelf depositional profiles. Shelf-margin trajectories, stratigraphic architectures, and facies proportions are a function of long-term accommodation trends expressed in second-order supersequences. These characteristics are modified by lateral variability in the underlying structural/tectonic setting and localized syndepositional faulting.
The stratigraphic equivalents of oceanic anoxic events 1a, 1b, 1d, 2, and 3 are documented in the Cretaceous section of south Texas. These oceanic anoxic events coincided with maximum flooding zones of supersequences and are linked to carbonate platform drowning events on four separate occasions. The occurrence of oceanic anoxic events is found to be a fundamental driver of carbonate platform morphology, faunal composition, and facies evolution in transgressive-regressive supersequences of the northern Gulf of Mexico.
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VARYING FLUX CONTROLS ON TIMESCALES OF AUTOGENIC STORAGE AND RELEASE PROCESSES IN FLUVIO-DELTAIC ENVIRONMENTS : TANK EXPERIMENTS
Erica Janette Powell, M.S. GeoSci
University of Texas at Austin, May 2011
Supervisor: Wonsuck Kim
49 pages, 58 references, 2 tables
Changes in external forcing having traditionally been the main area of interest in trying to understand paleo-depositional environments in sedimentary systems; however, autogenic variability has been rising in importance, while autogenic behavior has been thought of as a "noise" generator. Recently, autogenic variability has been rising in attention because decoupling allogenic signatures (externally driven) from the stratigraphic record requires robust understanding of autogenic variations (internally generated). This study aims to quantitatively measure autogenic processes under a range of flux conditions and to show that autogenic processes generate distinct signatures rather than random noise. We present data from a matrix of nine different tank experiments in order to systematically evaluate the effects of sediment flux and water discharge variations on the autogenic timescale of fluvial sediment storage and release processes and the implications of this data to the stratigraphic record. The sediment flux tow ater discharge ratio and the absolute values of these two discharges control the autogenic timescale. Variations in sediment supply yield two competing effects on the autogenic timescale. The primary sediment flux control causes a reduction in the autogenic timescale as an increase in sediment supply yields an increased rate of filling the "fluvial envelope" (the space between the maximum and minimum fluvial slopes obtained during storage and release events). In contrast, the secondary sediment flux control increases the size of the fluvial envelope and works against the primary sediment flux control. Increasing the water discharge increases the autogenic timescale by widening the fluvial envelope during the organization of the fluvial system and more importantly, diminishes the functionality of the secondary sediment control. A competition exists between these factors, causing a non-linear range of autogenic timescales for a given sediment flux to water discharge ratio. In the nine experiments here, as the ratio decreases, the secondary effects of variations in sediment supply are suppressed by the relatively high water discharge, and the timescale is more predictable using the primary sediment control. As the ratio increases, the secondary effects from sediment supply are enhanced by a poorly organized fluvial system, and the timescale converges to a narrow range. This suggests significant implications for autogenic sediment delivery and stratigraphic development in a wide range of discharge conditions in field cases.
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STRUCTURAL FRAMEWORK AND ITS INFLUENCE ON THE QUATERNARY-AGE SEQUENCE ARCHITECTURE OF THE NORTHERN SHELF OF TRINIDAD AND TOBAGO
Stefan Wayne Punnette, M.S. Geo. Sci.
University of Texas at Austin, August 2010
Supervisors: Paul Mann and Lesli J. Wood
166 pages, 85 references, 3 tables
The North Coast Marine Area (NCMA) extends across ~7000 km2 of the northern Trinidad and Tobago shelf in water depths between 50 to 200 meters. In 2009 the NCMA had two exploration blocks under active oil and gas exploration with gas production from the NCMA totaling ~ 1.1 tcf since 2002. All natural gas discovered to date in the NCMA has been interpreted as biogenic although one previous worker has speculated that a minor component of thermogenic gas is also present. The NCMA is located within a complex tectonic environment characterized by oblique strike-slip displacements between the Caribbean and South American plates at a rate of about 20 mm/yr. The main faults of the 200-km-wide plate boundary zone include: 1) the El Pilar right-lateral strike-slip fault zone to the south on the island of Trinidad and the Gulf of Paria which GPS results indicate to be largely inactive; 2) the North Coast fault zone (NCFZ) which coincides with the southern boundary of the Tobago basement terrane and appears to be slightly active with down-to-the-north, Miocene to recent oblique-slip movements on the NCFZ producing accommodation space for deposition of sediments along the northern shelf of Trinidad and Tobago; and 3) the Hinge Line fault zone (HLFZ) crossing through the NCMA and forming the focus of Chapter 2 of this thesis. The ~120 km long Hinge Line fault zone has an average east-northeast strike approximately parallel to the GPS-derived plate motion direction (080°), and is a sub-vertical, thick-skinned right-lateral strike-slip fault. Localized zones of transpression and transtension form locally where the trace of the fault deviates from the 080° direction of pure, right-lateral shear and these localized areas of complex faulting and folding provide important structural traps for Pliocene and Miocene gas reservoirs in the NCMA north of the HLFZ. Growth sequences along the HLFZ indicate that the fault activated in Miocene time and continues to up to the late Pleistocene (~500 k.y.) and in some areas forms active scarps on the seafloor. Structural maps and isochron maps were made for four horizons underlying the northern shelf of Trinidad including top Mesozoic basement, top Miocene, top Pliocene and seafloor. These maps support a change in terrigenous source area for the northern shelf of Trinidad: during the Miocene and early Pliocene, terrigenous sources were coming from the southeast through the Atlantic Ocean; where as during the mid-Pliocene to present the source area changed to the southeast through the Gulf of Paria.
The shallow seismic stratigraphic study of Chapter 3 analysed two Pleistocene fourth-order shelf and shelf-edge stratigraphic sequences deposited over the past ~500 k.y in the western part of the NCMA. New micropaleontologic data tied to a well through the two sequences B and C constrain the initial deposition of each sequence ~450 k.y (Sequence B) and ~260 k.y. (Sequence C). The lithologic well log shows that the sequences are sand, shale, and thin limestone. Seismic interpretation allows division of sequences B and C into eight system tracts which include: 1) lowstand system tracts, 2) transgressive system tracts, 3) highstand system tracts and 4) falling stage system tracts. Two lowstand systems tracts in sequences B and C are characterized by delta plain deposition of the Orinoco Delta with a north-eastward terrigenous source direction coming from the western side of Trinidad, through the Gulf of Paria. The falling stage systems tract of sequence C consists of a suite of ~20 – 45-m-high, 0.1° – 0.25°-inclined, and north-eastward-prograding muddy, shelf deltaic clinoforms marking the paleo-shelf edge. Fault controls penetrate into Sequence B and may have produced accommodation space but do not penetrate into overlying Sequence C which therefore must have been eustatically controlled. These Pleistocene sequences may provide a more recent analog for Miocene and Pliocene age sequences and reservoirs that form the highly productive horizons of the NCMA gas field.
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CARBON ISOTOPE ANALYSIS OF THE SOURCES AND MECHANISMS OF CO2 INPUT AND REMOVAL FROM CENTRAL TEXAS CAVE SYSTEMS
Ashley Elizabeth Quinn, B.S.
University of Texas at Austin, May 2010
Supervisors: Jay L. Banner and Dan Breecker
54 pages, 29 references, 4 tables
Speleothem calcite growth rate is a commonly used paleoclimate proxy. Seasonal variations in cave CO2 concentration (PCO2) are known to control speleothem growth. Thus, it is important to understand the mechanisms of CO2 input and removal from cave systems in order to better use speleothem calcite growth rate as a proxy. To this end, spatial and temporal variations in the atmosphere of several central Texas caves were studied over the course of a year. The stable isotope composition of the sources of CO2 in cave air were determined by measuring the δ13C values of cave-air CO2 samples collected from specific sites within the caves.
Cave-air PCO2 consistently increased and δ13C values consistently decreased with distance from the cave entrance. The values along these spatial transects vary seasonally towards higher δ13C values and lower PCO2 in the winter months (October-March). The linear relationship between δ13C and l/CO2 suggests that CO2 in the cave atmosphere is a mixture between atmospheric air (~380ppm, -8‰ δ13C, V-PDB) and a cave-end-member with low δ13C and high PCO2. The concentrations and δ13C values of cave-air CO2 were used to find the δ13C value of respired CO2 [δ13Cr] by correcting for atmospheric mixing and diffusion in the soil. The δ13C value of respired CO2 is generally higher in the summer and lower in the winter.
The seasonal- and regionally consistent variations in PCO2 and the δ13C value of cave-air CO2 support density-driven ventilation controlled by seasonal surface temperature changes as the major influence on cave-air CO2. The calculated δ13C values suggest that C3 organic material is the primary source of cave-air CO2 and that seasonal variation in the magnitude of photosynthetic discrimination and/or seasonal changes in the relative productivity of C3 vs. C4 vegetation influence the δ13C value of CO2 entering the cave.
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SUSPENSION OF BED MATERIAL OVER LATERAL SAND BARS IN THE LOWER MISSISSIPPI RIVER, SOUTHEASTERN LOUISIANA
Michael Towler Ramirez, MSGeoSci
University of Texas at Austin, December 2011
Supervisor: Mead Allison
122 pages, 62 references, 9 tables
Understanding specific pathways for sand transport in the lower reaches of large rivers, particularly the Mississippi, is the key to several geologic problems and environmental restoration efforts. Field studies were performed in the Mississippi River 75-100 kilometers upstream of the Gulf of Mexico outlet in April 2010 (water discharge: 23,000 m3 s-1), May 2010 (18,500-20,500 m3 s-1), and March 2011 (27,000 m3 s-1). Methods consisted of multibeam sonar bathymetric surveys, acoustic Doppler current profiler (ADCP) measurements of current velocity and acoustic backscatter, point-integrated isokinetic sampling of suspended sediment, and grab sampling of channel-bed sediment. Multibeam surveys of channel morphology revealed a 30-60 m deep thalweg, alternating between banks every 2-3 km. Opposite the thalweg between crossings were bedform-covered lateral sand bars extending nearly across the channel. Dune sizes nearest the thalweg ranged from 7 m wavelength and 0.3 m height in May 2010 to over 100 m wavelength and 2.3 m height in March 2011, with decreasing dune sizes away from the thalweg. Material comprising the dunes was well-sorted, fine-to-medium sand. Bedload transport rates increased exponentially with water discharge in April 2010 and March 2011 comparable to previous studies in this reach, though rates measured in May 2011 were well below predicted values. Average water velocities ranged from 1.3 m s-1 in May 2010 to over 2 m s-1 in March 2011. Skin-friction shear stress increased with water discharge, but displayed over an order of magnitude variation in the span of ten minutes at all measured discharges. Increasing suspended sand concentration and grain size with proximity to the bed was observed during all study periods, though this gradient was most pronounced in March 2011. Suspended sand concentrations were greatest over the center of lateral bars, and lowest in the thalweg. Washload discharge displayed a relationship with flood phase rather than water discharge, but total bed-material discharge was observed to increase exponentially with water discharge. Quadrant analysis of stationary time-series ADCP data from March 2011 revealed a high proportion of quadrant II and IV turbulent ejection and inrush events, which may be a mechanism responsible for the suspension of bed material.
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LATE CRETACEOUS TURBIDITES, HEIDRUN FIELD, NORWEGIAN CONTINENTAL SHELF
Sarika Kala Ramnarine, M.A.
University of Texas at Austin, May 2011
Supervisors: Lorena Moscardelli and William Fisher
82 pages, 26 references, 1 table
The Heidrun field is located in the Halten Terrace of the Mid-Norwegian Continental Shelf and is one of the first giant oil fields found on the Norwegian Sea. Modern 3D seismic reflection data acquired over the field, as well as well data were used to define the key structural and stratigraphic elements within the study area. The basic geologic history of the Heidrun field is typical of most North Sea plays, and includes Triassic rift sequences that are masked by the reactivation of bounding faults that were active during the Jurassic rift phase. This rifting phase was followed by deposition of marine black shales and subsequent carbonaceous shales during the Latest Jurassic to Earliest Cretaceous. The next sequence was characterized by the deposition of Paleocene-Eocene boundary tuffs, which were formed due to volcanism associated with a rifting event that separated Norway and Greenland. Finally, an Eocene to present passive margin marine sequence is dominant over the study area that is mainly composed by glacial deposits. Traditional reservoir intervals within the Heidrun field are located within the Jurassic age inter-rift sequence. However, most recently Cretaceous-age turbidites have been explored in the Norwegian and North Sea as possible targets with some success. These Cretaceous turbidites are traditionally found as basin floor fan deposits within rifted deeps along the Norwegian continental shelf and are believed to be sourced from localized erosion of Jurassic- age rifted highs. Data within our study area revealed the existence of a deep-water Cretaceous age wedge located within the downthrown hanging wall of several smaller half-grabens formed on the Halten Terrace. Seismic attribute extractions taken within this Cretaceous wedge show the presence of several elongate to lobate bodies that seem to cascade over fault-bounded terraces associated with the rifted structures. These high amplitude elongated bodies are interpreted as proximal sedimentary conduits that are time equivalent to the Cretaceous basin floor fans located in more distal portions of the basin to the west. Several wells penetrate the updip, tilted half-graben hanging walls which are believed to be sourcing these turbidite systems. These half graben fills have the potential to contain high quality Cretaceous sandstones that might represent a potential new reservoir interval within the Heidrun field.
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EMPIRICAL METHODS FOR COMPARING GOVERNANCE STRUCTURE
Timothy Patrick Reinhardt, Master of Arts in Energy and Earth Resources
University of Texas at Austin, May 2009
Supervisor: Christopher Jablonowski
53 pages, 34 references
In the Gulf of Mexico offshore exploration and production (E&P) industry, oil company decision-makers desire to drill wells for exploration or development purposes. While a number of organizational arrangements are employed by firms in the E&P industry, most drilling arrangements can be categorized as one of two types of organizational structure based upon the allocation of planning and supervision responsibilities. Companies can employ internal drilling organizations (best-efforts) to plan and manage their drilling operations or choose to contract externally (turnkey) for these activities. The decision made by the exploration and production company as to which organizational form to employ can have significant impacts on the efficiency and profitability of any given well or drilling campaign. This research examines this choice of governance structure. This paper will examine the drivers of this decision using the theory of transaction cost economics. Regression models are specified and estimated for the turnkey drilling decision, and for the underlying cost functions of best-efforts and turnkey drilling. Results provide support for the transaction cost hypothesis as significant in the choice of governance.
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THE EFFECTS OF CHANNEL MIGRATION ON POINT BAR DEVELOPMENT IN THE LOWER TRINITY RIVER, TEXAS
Elizabeth Rinehart, BS, Department of Geological Sciences
University of Texas at Austin, May 2011
Supervisor: David Mohrig
61 pages, 15 references, 4 tables
Sand-bed rivers are physically dynamic and undergo lateral migration. In areas of sediment transport equilibrium, often associated with higher rates of lateral migration, healthy point bars are built. Because the lower Trinity River from Lake Livingston Dam to Galveston Bay is an excellent example of such a sand-bed coastal river and because it experiences approximate sediment transport equilibrium in the middle section, it was chosen as the field site. This middle section, or Zone 2, is bounded upstream by a zone of dam influence and bounded downstream by a zone of backwater influence.
Two point bars from Zone 2 of the Trinity were trenched and surveyed. There was also bathymetric data taken around each point bar and photographs and sediment samples taken from each of the trenches. These measurements, along with four sets of aerial photos corresponding to the years 1952, 1968/1972, 1996, and 2009, were used to study the migration, shape, sedimentary structures, topography, subaerial extent, and trends in grain size for both point bars in this study.
Using the aerial photographs, average rates of lateral migration for the channel were calculated. I also analyzed the shapes of the two point bars; the downstream point bar, Bar 2, has the classic crescent shape, while the upstream point bar, Bar 1, which experienced a progressive, meander-loop cutoff between 1996 and 2009, deviates from the crescent shape. This deviation in map-view shape is likely because of the aforementioned cutoff. The survey data showed a very steep slope at the upstream end of Bar 1.1 attribute this high bar slope to the steep bank of the channel sidewall itself, a consequence of the loop cutoff. The grain size data from Bar 1 's trench one, the most upstream trench, showed a trend of decreasing grain size from the river's edge to the bar top. The other trenches showed no clear trends in grain size. This is likely connected to the considerably shallower bar slope topography associated with the downstream end of Bar 1 and all of Bar 2. Finally, the sedimentary structures observed in trench one of Bar 1 included a unique zone of climbing ripples at the bar top with an underlying zone built entirely of dune strata. This zonal change in structures and the lack of gravel size material on the bar top at trench one is attributed to the uniquely steep topography of the upstream end of Bar 1. All of this data seems to indicate that channel migration can have an effect on point bar development, particularly on bar shape and style of sediment deposition associated with bar growth.
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RISK MANAGEMENT STRATEGIES AND PORTFOLIO ANALYSIS FOR ELECTRICITY GENERATION PLANNING AND INTEGRATION OF RENEWABLE PORTFOLIO STANDARDS
Stephanie Michelle Ritter, M.A.
University of Texas at Austin, December 2009
Supervisor: David Spence
74 pages, 29 references, 1 table
Renewable Portfolio Standards (RPS) require electricity providers to supply a minimum fixed percentage or total quantity of customer load from designated renewable energy resources by a given date. These policies have become increasingly prevalent in the past decade as state governments seek to increase the use of renewable energy sources. As a policy tool, RPS provide a cost-effective, market-based approach for meeting targets which promote greater use of renewable energy in both regulated and deregulated markets.
To facilitate the obtainment of Renewable Portfolio Standards, most states allow the trading of Renewable Energy Credits (RECs). RECs represent the environmental attributes of renewable energy generation which are decoupled from the generated power. These credits are created along with the generation of renewable energy, decoupled from energy generation, tracked by regional systems, and eventually purchased by retail suppliers to fulfill their RPS obligations.
As of April 2010, RPS have been passed into law in 29 states and Washington D.C. and an additional 6 states have non-mandatory renewable portfolio goals however the U.S. government has yet to enact a Federal Renewable Portfolio Standard. Although the final requirements and details of a Federal RPS arc undecided, federal standards would be unlikely to preempt or override stale programs which arc already in place. A key concern regarding the passage of a federal RPS is that a national REC market would result in a shift of wealth from states with few renewable energy resources and limited resource potential to regions richer in renewable resources. Because of the implications that a federal renewable portfolio standard would have on the economy, the environment, and the equitable treatment of all the stales, many issues and concerns must be resolved before federal standards will be passed into law.
A hypothetical case study for an electric utility generation planning decision that includes obligations to meet Renewable Portfolio Standard is presented here. A framework is provided that allows decision makers and strategic planning teams lo: assess their business situation, identify objectives of generation planning, determine the relative weights of the objectives, recognize tradeoffs, and create an efficient portfolio using Portfolio Theory. The case study follows the business situation for Austin Energy as it seeks to meet Texas State RPS and mandates set by Austin City Council and prepares for potential National RPS legislation.
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REGIONAL STRUCTURE, STRATIGRAPHY, AND HYDROCARBON POTENTIAL OF THE MEXICAN SECTOR OF THE GULF OF MEXICO
Anthony Byron Rodriguez, M.S. Geo. Sci.
University of Texas at Austin, August 2011
Co-Supervisors: Paul Mann and William E. Galloway
177 pages, 127 references, 2 tables
I have compiled digital seismic and well data over a region of approximately 700,000 km2 to better improve the correlation of the Mexican sector of the Gulf of Mexico (MGOM) with the better studied and more explored U.S. sector. I have ~25,000 km of regional 2D lines that were collected by the University of Texas in the 1970's. I have digitized data from published PEMEX data from the MGOM using SEG-Y converter software and incorporated these data into my seismic grid. Using these data, I interpreted and correlated 20 surfaces that range in age from Late Jurassic to Recent. The combined shelf-slope-basin dataset from the MGOM allows for correlation of units from the deepwater MGOM, across into the Mexican Ridges passive margin foldbelt, and onto the Mexican shelf. I have also incorporated seismic data from the offshore Chicxulub crater and correlated units in the Yucatan platform area with the deepwater MGOM. This regional data set indicates that normal, growth faulting linked with downdip toe thrusts and folds of the Mexican Ridges initiated in post-Middle Miocene time and are therefore unrelated to the earlier Paleogene Laramide uplift deformation phase. Shelf-slope-deep basin seismic facies of Eocene and Oligocene units show an influx of clastic materials linked with regional uplift and volcanic events affecting central Mexico during this period. I propose that the deepwater folds of the Mexican Ridges accompanied shelf-edge gravity sliding and normal faulting activated during accelerated Oligo-Miocene uplift, regional volcanic activity, and erosion of the Mexican landmass. Downdip sliding occurred on the seaward-dipping top Cretaceous carbonate unit (7° to 13°) along with overlying horizons that range in dip from 1° to 2°. Shelf¬slope-deep basin seismic facies of the Paleocene units around the Yucatan peninsula suggest a sediment-starved and slide-free carbonate margin with a current basinward dip of approximately 12° and significantly greater than those dips observed along the present-day eastern Gulf of Mexico. Based on the seismic interpretations and plate reconstructions, I propose four major tectonosequences fill the Gulf of Mexico basin: 1) A Late Jurassic to Late Cretaceous passive margin phase; 2) a Late Cretaceous to Late Eocene Laramide deformational phase; 3) a Late Eocene to Middle Miocene passive margin phase; and 4) a Late Miocene to Recent Neogene deformational phase.
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EVALUATING ENHANCED HYDROLOGICAL REPRESENTATIONS IN NOAH LSM OVER TRANSITION ZONES: AN ENSEMBLE-BASED APPROACH TO MODEL DIAGNOSTICS
Enrique Xavier Rosero Ramirez, Ph.D.
University of Texas at Austin, December 2009
Supervisor: Zong-Liang Yang
232 pages, 198 references, 15 tables
This work introduces diagnostic methods for land surface model (LSM) evaluation that enable developers to identify structural shortcomings in model parameterizations by evaluating model ‘signatures’ (characteristic temporal and spatial patterns of behavior) in feature, cost-function, and parameter spaces. The ensemble-based methods allow researchers to draw conclusions about hypotheses and model realism that are independent of parameter choice.
I compare the performance and physical realism of three versions of Noah LSM (a benchmark standard version [STD], a dynamic-vegetation enhanced version [DV], and a groundwater-enabled one [GW]) in simulating high-frequency near-surface states and land-to-atmosphere fluxes in-situ and over a catchment at high-resolution in the U.S. Southern Great Plains, a transition zone between humid and arid climates. Only at more humid sites do the more conceptually realistic, hydrologically enhanced LSMs (DV and GW) ameliorate biases in the estimation of root-zone moisture change and evaporative fraction. Although the improved simulations support the hypothesis that groundwater and vegetation processes shape fluxes in transition zones, further assessment of the timing and partitioning of the energy and water cycles indicates improvements to the movement of water within the soil column are needed. Distributed STD and GW underestimate the contribution of baseflow and simulate too-flashy streamflow.
This work challenges common practices and assumptions in LSM development and offers researchers more stringent model evaluation methods. I show that, because of equifinality, ad-hoc evaluation using single parameter sets provides insufficient information for choosing among competing parameterizations, for addressing hypotheses under uncertainty, or for guiding model development. Posterior distributions of physically meaningful parameters differ between models and sites, and relationships between parameters themselves change. ‘Plug and play’ of modules and partial calibration likely introduce error and should be re-examined. Even though LSMs are ‘physically based,’ model parameters are effective and scale-, site- and model-dependent. Parameters are not functions of soil or vegetation type alone: they likely depend in part on climate and cannot be assumed to be transferable between sites with similar physical characteristics.
By helping bridge the gap between the model identification and model development, this research contributes to the continued improvement of our understanding and modeling of environmental processes.
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AIRBORNE LIDAR-AIDED COMPARATIVE FACIES ARCHITECTURE OF YATES FORMATION (PERMIAN) MIDDLE TO OUTER SHELF DEPOSITIONAL SYSTEMS, MCKITTRICK CANYON, GUADALUPE MOUNTAINS, NEW MEXICO AND WEST TEXAS
Cari Elizabeth Sadler, M.A.
University of Texas at Austin, December 2010
Supervisor: Charles Kerans
57 pages, 35 references, 1 table
The eastern side of the Guadalupe Mountains, located in New Mexico and west Texas, represents an erosional profile along the Capitan reef margin. A complete shelf-to-basin exposure of the Upper Permian Capitan shelf margin is found on the north wall of North McKittrick Canyon, which is nearly perpendicular to the Capitan reef margin. An excellent 2-D sequence stratigraphic framework for upper Permian backreef facies has been developed by previous workers for North McKittrick Canyon (Tinker, 1998) and Slaughter Canyon (Osleger, 1998), forming the basis for observations in this study.
The goal of this study is to describe the sequence stratigraphic architecture of the Yates Formation, focusing on the Y4-Y6 high-frequency sequences (HFSs) found in the middle to outer shelf depositional systems, and to illustrate the use of airborne lidar data to quantitatively map at the cycle-scale. Seven measured sections were taken in North McKittrick Canyon. From airborne lidar, 3-D geometries of key sedimentary and structural features were mapped in Polyworks, in addition to the sequence boundaries delineating the Yates 4-6 HFSs.
In general, major cycles exhibit asymmetry and shoal upward. Cycle boundaries are sometimes hard to delineate due to amalgamation, particularly in the shelf crest. High-frequency sequences are commonly asymmetric; they deepen and thicken upward toward the maximum flooding surface, and the boundaries between HFSs are usually marked by thick siltstones. Major HFS boundaries can be mapped across the entire dataset, and some component cycles can be observed for minimum distances of one kilometer in an updip-downdip direction. Also, some facies tract dimensions can be estimated directly from the lidar data. Measured sections indicate that the shelf crest facies tract shifts seaward with each successive HFS, while the outer shelf facies tract steps landward.
Future work that could be done with the Y4-Y6 HFSs includes 8-10 more measured sections, collection of samples for thin sections, and tracing out of contacts between facies tracts. Extensive lidar data interpretation needs to be done so that digital outcrop models demonstrating facies distributions can be produced. This would enable the development of an outcrop analog model to mixed carbonate-siliciclastic reservoirs, which would be unprecedented in this area.
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CENOZOIC STRUCTURAL EVOLUTION OF THE EASTERN MARGIN OF THE MIDDLE MAGDALENA VALLEY BASIN, COLOMBIA: INTEGRATION OF STRUCTURAL RESTORATIONS, LOW-TEMPERATURE THERMOCHRONOLOGY, AND SANDSTONE PETROGRAPHY
Carlos Javier Sánchez
University of Texas at Austin, August 2011
Supervisor: Brian K. Horton
114 pages, 119 references, 9 tables
Structural analysis of surface and subsurface data from the Middle Magdalena Valley basin and Eastern Cordillera fold-thrust belt to construct a kinematic model for its Cenozoic structural and stratigraphic evolution. The La Salina west-vergent thrust system marks the boundary between the Paleogene foreland basin of the Middle Magdalena basin and the Eastern Cordillera fold-thrust belt. New low-temperature thermochonological and sandstone petrographic analyses provide constraints on ages of thrust deformation and sediment dispersal. Apatite fission track (AFT) and U-Th/He thermochronological results show the timing of three structural events along the La Salina fault system: (1) late Eocene-early Oligocene (~43–35 Ma) initial hanging wall exhumation; (2) continued middle Miocene (~15 Ma) exhumation; and (3) continued but more rapid late Miocene (~12–3 Ma) hanging wall exhumation. Vitrinite reflectance results provide estimates of maximum burial depths for the hanging wall of the La Salina fault ranging from 4 to 6 km., this depth of burial estimates constrain the basin geometry during its late Eocene to late Miocene evolution.
The eastern hanging wall of the La Salina fault displays a broad anticline-syncline pair affecting Cretaceous to Eocene strata with no significant faulting, whereas the western footwall contains a complex series of tight, thrust-related folds in Eocene-Quaternary strata. For foreland basin province, a proposed triangle zone accommodates a small amount of east-west shortening (< 1000 m) along the frontal thrust system by east-vergent backthrusting within a broader passive-roof duplex. East-west shortening in the Cenozoic stratigraphic section was also accommodated by detachment folding, which produced localized areas of steep dips. In the proposed kinematic restoration, the most recent phase of deformation represents out-of-sequence reactivation of the La Salina fault that is consistent with irregular crosscutting relationships of some footwall structures.
Earliest exhumation by ~45–30 Ma in the Eastern Cordillera fold-thrust belt province matches (1) an increased proportion of sedimentary lithic fragments; and (2) a high degree of compositional maturity (Q88F4Lf8). Exhumation since ~15 Ma in the foreland province coincides with (1) the highest accumulation rates observed for the upper Miocene Real Group; and (2) a decrease in compositional maturity (Q55F8Lf36).
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CONTROLS ON SEDIMENTARY PROCESSES AND 3D STRATIGRAPHIC ARCHITECTURE OF A MID-MIOCENE TO RECENT, MIXED CARBONATE-SILICICLASTIC CONTINENTAL MARGIN : NORTHWEST SHELF OF AUSTRALIA
Carla Maria Sanchez Ph.D.
University of Texas at Austin, May 2011
Supervisors: Ronald Steel and Craig Fulthorpe
141 pages, 124 references
Determining the relative importance of processes that control the generation and preservation of continental margin stratigraphy is fundamental to deciphering the history of geologic, climatic and oceanographic forcing imprinted on their sedimentary record. The Northern Carnarvon Basin (NCB) of the North West Shelf of Australia has been a site of passive margin sedimentation throughout the Neogene. Cool-water carbonate sedimentation dominated during the early-middle Miocene, quartz-rich siliciclastics prograded over the shelf during the late-middle Miocene, and carbonate sedimentation resumed in the Pliocene. Middle Miocene to Pliocene siliciclastics were deposited as clinoform sets interpreted as delta lobes primarily based on their plan-view morphology and their relief of 40-100 m. Shelf-edge trajectory analysis suggests that part of this stratigraphic succession was built during a long-term, third order, regressive phase, producing shelf-edge deltas, followed by an aggradational episode. These trends appear to correlate with third-order global eustatic cycles. Slope incisions were already conspicuous on the slope before deltas reached the shelf-break. Nevertheless, slope gullies immediately downdip from the shelf-edge deltas are wider and deeper (>1 km wide, ~100 m deep) than coeval incisions that are laterally displaced from the deltaic depocenter (~0.7 km wide, ~25 m deep). This change in gully morphology is likely the result of greater erosion by sediment gravity flows sourced from shelf-edge deltas. Total late-middle to late Miocene margin progradation increased almost three times from 13 km in the southwest to 34 km in the northeast, where shelf-edge deltas were concentrated.
Flat-topped carbonate platforms seem to have initiated on subtle antecedent topographic highs resulting from these deltaic lobes. A reduction of siliciclastic supply to the outer paleo-shelf during the Pliocene combined with the onset of a southwestward-flowing, warm-water Leeuwin Current (LC) most likely controlled the initiation of these carbonate platforms. These platforms display marked asymmetry, likely caused by an ancestral LC, which created higher-angle, upcurrent platform margins, and lower-angle, downcurrent clinoforms. The along-strike long-term migration trend of the platforms could be the result of differential subsidence. These platforms constitute the first widespread accumulation of photozoan carbonates in the Northern Carnarvon Basin. They became extinct after the mid-Pleistocene when the LC weakened or became more seasonal.
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COMPLEXITY IN RIVER-GROUNDWATER EXCHANGE DUE TO PERMEABILITY HETEROGENEITY, IN-STREAM FLOW OBSTACLES, AND RIVER STAGE FLUCTUATIONS
Audrey Hucks Sawyer, Ph.D.
University of Texas at Austin, May 2011
Supervisor: M. Bayani Cardenas
150 pages, 141 references, 8 tables
River-groundwater exchange (hyporheic exchange) influences temperature, water chemistry, and ecology within rivers and alluvial aquifers. Rates and patterns of hyporheic exchange depend on riverbed permeability, pressure gradients created by current-obstacle interactions, and river stage fluctuations. I demonstrate the response of hyporheic exchange to three examples of these driving forces: fine-scale permeability structure in cross-bedded sediment, current interactions with large woody debris (LWD), and anthropogenic river stage fluctuations downstream of dams.
Using numerical simulations, I show that cross-bedded permeability structure increases hyporheic path lengths and modifies solute residence times in bedforms. The tails of residence time distributions conform to a power law in both cross-bedded and internally homogeneous riverbed sediment. Current-bedform interactions are responsible for the decade-scale tails, rather than permeability heterogeneity.
Like bedforms, wood debris interacts with currents and drives hyporheic exchange. Laboratory flume experiments and numerical simulations demonstrate that the amplitude of the pressure wave (and thus hyporheic exchange) due to a channel-spanning log increases with channel Froude number and blockage ratio (log diameter : flow depth). Upstream from LWD, downwelling water transports the river's diel thermal signal deep into the sediment. Downstream, upwelling water forms a wedge of buffered temperatures. Hyporheic exchange associated with LWD does not significantly impact diel surface water temperatures. I tested these fluid and heat flow relationships in a second-order stream in Valles Caldera National Preserve (NM). Log additions created alternating zones of upwelling and downwelling in a reach that was previously losing throughout. By clearing LWD from channels, humans have reduced hydrologic connectivity at the meter-scale and contributed to degradation of benthic and hyporheic habitats.
Dams also significantly alter hydrologic connectivity in modern rivers. Continuous water table measurements show that 15 km downstream of the Longhorn dam (Austin, Texas), river stage fluctuations of almost 1 m induce a large, unsteady hyporheic exchange zone within the bank. Dam-induced hyporheic exchange may impact thermal and geochemical budgets for regulated rivers. Together, these three case studies broaden our understanding of complex drivers of hyporheic exchange in small, natural streams as well as large, regulated rivers.
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FAILURE MECHANICS, TRANSPORT BEHAVIOR, AND MORPHOLOGY OF SUBMARINE LANDSLIDES
Derek Edward Sawyer, Ph.D.
University of Texas at Austin, December 2010
Supervisor: Peter B. Flemings
141 pages, 196 references, 7 tables
Submarine landslides retrogressively fail from intact material at the headwall and then become fluidized by strain weakening; the final deposits of these flows have low porosity, which controls their character in seismic reflection data. Submarine landslides occur on the open slope and also localized areas including margins of turbidite channel-levee systems. I develop and quantify this model with 3-D seismic reflection data, core and log data from Integrated Ocean Drilling Program Expedition 308 (Ursa Basin, Gulf of Mexico), flume experiments, and numerical modeling. At Ursa, multiple submarine slides over the last 60 ky are preserved as mass transport deposits (MTDs). Retrogression proceeded from an initial slope failure that created an excavated headwall, which reduced the horizontal stress behind the headwall and resulted in normal faults. Fault blocks progressively weakened until the gravitational driving stress imposed by the bed slope exceeded soil strength, which allowed the soil to flow for more than 10 km away from the source area. The resulting MTDs have lower porosity (higher bulk density) relative to non-failed sediments, which ultimately produces high amplitude reflections at the base and top of MTDs. In the laboratory, I made weak (low yield strength) and strong flows (high yield strength) from mixtures of clay, silt, and water. Weak flows generate turbidity currents while moving rapidly away from the source area. They create thin and long deposits with sinuous flow features, and leave behind a relatively smooth and featureless source area. In contrast, strong flows move slowly, do not generate a turbidity current, and create blocky, highly fractured source areas and short, thick depositional lobes. In Pleistocene turbidite channels of the Mississippi Fan, deep-seated rotational failures occurred in the flanking levees. The rotational failures displaced material into the channel from below where it became eroded by turbidity flows. This system achieved a delicate steady state where levee deposition and displacement along the fault into the channel was balanced by erosion rate of turbidity flows. This work enhances our understanding of geohazards and margin evolution by illuminating coupled processes of sedimentation, fluid flow, and deformation on passive continental margins.
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COMPRESSION AND PERMEABILITY BEHAVIOR OF NATURAL MUDSTONES
Julia Schneider, Ph.D.
University of Texas at Austin, December 2011
Supervisor: Peter B. Flemings
302 pages, 161 references, 25 tables
Mudstones compose nearly 70% of the volume of sedimentary basins, yet they are among the least studied of sedimentary rocks. Their low permeability and high compressibility contribute to overpressure around the world. Despite their fundamental importance in geologic processes and as seals for anthropogenic-related storage, a systematic, process-based understanding of the interactions between porosity, compressibility, permeability, and pore-size distribution in mudstones remains elusive.
I use sediment mixtures composed of varying proportions of natural mudstone such as Boston Blue Clay or Nankai mudstone and silt-sized silica to study the effect of composition on permeability and compressibility during burial. First, to recreate natural conditions yet remove variability and soil disturbance, I resediment all mixtures in the laboratory to a total stress of 100 kPa. Second, in order to describe the systematic variation in permeability and compressibility with clay fraction, I uniaxially consolidate the resedimented samples to an effective stress equivalent to about 2 km of burial under hydrostatic conditions. Scanning electron microscope images provide insights on microstructure.
My experiments illuminate the controls on mudstone permeability and compressibility. At a given porosity, vertical permeability increases by an order of magnitude for clay contents ranging from 59% to 34% by mass whereas compressibility reduces by half at a given vertical effective stress. I show that the pore structure can be described by a dual-porosity system, where one rock fraction is dominated by silt where large pores are present and the majority of flow occurs and the other fraction is dominated by clay where limited flow occurs. I use this concept to develop a coupled compressibility-permeability model in order to predict porosity, permeability, compressibility, and coefficient of consolidation. These results have fundamental implications for a range of problems in mudstones. They can be applied to carbon sequestration, hydrocarbon trapping, basin modeling, overpressure distribution and geometry as well as morphology of thrust belts, and an understanding of gas-shale behavior.
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DETECTION OF PRODUCTION-INDUCED TIME-LAPSE SIGNATURES BY GEOPHYSICAL (SEISMIC AND CSEM) MEASUREMENTS
Alireza Shahin, PhD
University of Texas at Austin, May 2011
Supervisors: Paul L. Stoffa and Robert H. Tatham
While geophysical reservoir characterization has been an area of research for the last three decades, geophysical reservoir monitoring, time-lapse studies, have recently become an important geophysical application. Generally speaking, the main target is to detect, estimate, and discriminate the changes in subsurface rock properties due to production. This research develops various sensitivity and feasibility analyses to investigate the effects of production-induced time-lapse changes on geophysical measurements including seismic and controlled-source electromagnetic (CSEM) data. For doing so, a realistic reservoir model is numerically simulated based on a prograding near-shore sandstone reservoir. To account for the spatial distribution of petrophysical properties, an effective porosity model is first simulated by Gaussian geostatistics. Dispersed clay and dual water models are then efficiently combined with other well-known theoretical and experimental petrophysical correlations to consistently simulate reservoir model parameters. Next, the constructed reservoir model is subjected to numerical simulation of multi-phase fluid flow to replicate a waterflooding scenario of a black oil reservoir and to predict the spatial distributions of fluid pressure and saturation. A modified Archie's equation for shaly sandstones is utilized to simulate rock resistivity. Finally, a geologically consistent stress-sensitive rock physics model, combined with the modified Gassmann theory for shaly sandstones, is utilized to simulate seismic elastic parameters. As a result, the comprehensive petro-electro-elastic model developed in this dissertation can be efficiently utilized in sensitivity and feasibility analyses of seismic/CSEM data with respect to petrophysical properties and, ultimately, applied to reservoir characterization and monitoring research.
Using the resistivity models, a base and two monitor time-lapse CSEM surveys are simulated via accurate numerical algorithms. 2.5D CSEM modeling demonstrates that a detectable time-lapse signal after 5 years and a strong time-lapse signal after 10 years of waterflooding are attainable with the careful application of currently available CSEM technology.
To simulate seismic waves, I employ different seismic modeling algorithms, one-dimensional (1D) acoustic and elastic ray tracing, 1D full elastic reflectivity, 2D split-step Fourier plane-wave (SFPW), and 2D stagger grid explicit finite difference (FD). My analyses demonstrate that acoustic modeling of an elastic medium is a good approximation up to ray parameter (p) equal to 0.2 sec/km. However, at p=0.3 sec/km, differences between elastic and acoustic wave propagation is the more dominant effect compared to internal multiples. Here, converted waves are also generated with significant amplitudes compared to primaries and internal multiples.
I also show that time-lapse modeling of the reservoir using SFPW approach is very fast compared to FD, 100 times faster for my case here. It is capable of handling higher frequencies than FD. It provides an accurate image of the waterflooding process comparable to FD. Consequently, it is a powerful alternative for time-lapse seismic modeling.
I conclude that both seismic and CSEM data have adequate but different sensitivities to changes in reservoir properties and therefore have the potential to quantitatively map production-induced time-lapse changes.
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SENSITIVITY OF SEISMIC RESPONSE TO VARIATIONS IN THE WOODFORD SHALE, DELAWARE BASIN, WEST TEXAS
Na Shan, M.S.Geo.Sci.
University of Texas at Austin, December 2010
Supervisor: Robert H. Tatham
106 pages, 69 references, 3 tables
The Woodford Shale is an important unconventional oil and gas resource. It can act as a source rock, seal and reservoir, and may have significant elastic anisotropy, which would greatly affect seismic response. Understanding how anisotropy may affect the seismic response of the Woodford Shale is important in processing and interpreting surface reflection seismic data.
The objective of this study is to identify the differences between isotropic and anisotropic seismic responses in the Woodford Shale, and to understand how these anisotropy parameters and physical properties influence the resultant synthetic seismograms. I divide the Woodford Shale into three different units based on the data from the Pioneer Reliance Triple Crown #1 (RTC #1) borehole, which includes density, gamma ray, resistivity, sonic, dipole sonic logs, part of imaging (FMI) logs, elemental capture spectroscopy (ECS) and X-ray diffraction (XRD) data from core samples. Different elastic parameters based on the well log data are used as input models to generate synthetic seismograms. I use a vertical impulsive source, which generates P-P, P-SV and SV-SV waves, and three component receivers for synthetic modeling. Sensitivity study is performed by assuming different anisotropic scenarios in the Woodford Shale, including vertical transverse isotropy (VTI), horizontal transverse isotropy (HTI) and orthorhombic anisotropy.
Through the simulation, I demonstrate that there are notable differences in the seismic response between isotropic and anisotropic models. Three different types of elastic waves, i.e., P-P, P-SV and SV-SV waves respond differently to anisotropy parameter changes. Results suggest that multicomponent data might be useful in analyzing the anisotropy for the surface seismic data. Results also indicate the sensitivity offset range might be helpful in determining the location for prestack seismic amplitude analysis. All these findings demonstrate the potentially useful sensitivity parameters to the seismic data.
The paucity of data resources limits the evaluation of the anisotropy in the Woodford. However, the seismic modeling with different type of anisotropy assumptions leads to understand what type of anisotropy and how this anisotropy affects the change of seismic data.
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TECTONIC RELATIONSHIPS BETWEEN ULTRA-HIGH PRESSURE SUBDUCTION COMPLEX ASSEMBLAGES AND CO-EXISTING GRANITOIDS, SIVRIHISAR MASSIF, TURKEY
Timothy Andrew Shin, B.S.
University of Texas at Austin, May 2011
Supervisor: Elizabeth J. Catlos
101 pages, 72 references, 9 tables
This study developed a model to explain a very high pressure/low-temperature exhumed metamorphic accretionary subduction complex intruded by granitoid plutons in the Sivrihisar Massif in western Turkey. The Sivrihisar Massif is a portion of the Tavşanlı Zone metamorphic subduction complex which (in conjunction with the Izmir-Ankara-Erzincan ophiolite suite) is a remnant of the Late Cretaceous to Eocene closure of the northern branch of the NeoTethyan Ocean. High pressures and very low temperatures have been reported for rocks from the area, and are thought to be one of the deepest portions of a subduction zone ever exhumed. The relationship of these granitoid plutons to the subduction complex is not well-known. This study used techniques never before applied to the Sivrihisar area rocks, including in situ U-Pb zircon ion microprobe dating with Secondary Ion Mass Spectrometer and relative barometry of Na and Ca amphibole analysis via electron microprobe. These two techniques are combined with major and trace element geochemistry and textural analysis via back-scattered electron and cathodoluminescence imagery to gain new insights on the region's geologic history. Major and trace element geochemistry and zircon U-Pb ages from two granitoid samples from the Sivrihisar Pluton and one granitoid sample from the Kaymaz Pluton and zircon U-Pb ages from one chlorite-schist sample associated with the high-pressure/low-temperature metamorphic terrane suggest calc-alkalic granitoid crystallization occurred from Late Cretaceous (79.9±8.6 Ma) to Early Oligocene (33.3±2.0 Ma) sourced from a subducting slab and later mixed with syn-collisional and within-plate granitoid magmas while undergoing fractional crystallization. Subduction of the Tavşanlı Zone may have been occurring as early as the Cambrian (564.8±32.1 Ma) or Carboniferous (310.8±6.0 Ma) with metamorphism of detrital zircons from the Paleoproterozoic (1870±102 Ma and 1646±81 Ma). Na and Al contents in amphiboles from three samples of the high-pressure/low-temperature metamorphic rocks reveal relative pressures higher than that observed in subduction zones like the Franciscan, Sanbagawa, and very high pressure zones like that of the Qiantang Plateau in Tibet. The new tectonic model developed in this study explains granitoid intrusion into the metamorphic complex of the subduction margin that created the Tavşanlı Zone by melts derived from the younger Afyon subduction zone to the south. Rapid exhumation of the metamorphic terrane and entrainment of the granitoids is accommodated in a multistage poly-subduction zone environment that progressively transitions to collision from north to south over time. The Sivrihisar and Kaymaz Plutons are a part of a suite of Afyon slab generated arc magmatic rocks that were originally intrusive to the Tavşanlı Zone but later became syn-collisional. Alternatively, the granitoids are sourced from subducting slab breakoff.
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SEDIMENTARY, STRUCTURAL, AND PROVENANCE RECORD OF THE CIANZO BASIN, PUNA PLATEAU-EASTERN CORDILLERA BOUNDARY, NW ARGENTINA
Benjamin Charles Siks, MS GeoSci
University of Texas at Austin, May 2011
Supervisor: Brian K. Horton
The fault-bounded Cianzo basin represents a Cenozoic intermontane depocenter between the Puna plateau and Eastern Cordillera of the central Andean fold-thrust belt in northern Argentina. New characterizations of fold-thrust structure, nonmarine sedimentation, and sediment provenance for the shortening-induced Cianzo basin at 23°S help constrain the origin, interconnectedness, and subsequent uplift and exhumation of the basin, which may serve as an analogue for other intermontane hinterland basins in the Andes. Structural mapping of the Cianzo basin reveals SW and NE-plunging synclines within the ›6000 m-thick, upsection coarsening Cenozoic clastic succession in the shared footwall of the N-striking, E-directed Cianzo thrust fault and transverse, NE-striking Hornocal fault. Growth stratal relationships within upper Miocene levels of the succession indicate syncontractional sedimentation directly adjacent to the Hornocal fault.
Measured stratigraphic sections and clastic sedimentary lithofacies of Cenozoic basin-fill deposits show upsection changes from (1) a distal fluvial system recorded by fine-grained, paleosol-rich, heavily bioturbated sandstones and mudstones (Paleocene-Eocene Santa Bárbara Subgroup, ~400 m), to (2) a braided fluvial system represented by cross-stratified sandstones and interbedded mudstones with 0.3 to 8 m upsection-fining sequences (Upper Eocene-Oligocene Casa Grande Formation, ~1400 m), to (3) a distributary fluvial system in the distal sectors of a distributary fluvial megafan represented by structureless sheetflood sandstones, stratified pebble conglomerates and sandstones, and interbedded overbank mudstones (Miocene Río Grande Formation, ~3300 m), to (4) a proximal alluvial fan system with thick conglomerates interbedded with thin discontinuous sandstone lenses (upper Miocene Pisungo Formation, ~1600 m).
New 40Ar/39Ar geochronological results for five interbedded volcanic tuffs indicate distributary fluvial deposition of the uppermost Río Grande Formation from 16.31 ± 0.6 Ma to 9.69 ± 0.05 Ma. Sandstone petrographic results show distinct upsection trends in lithic and feldspar content in the Casa Grande, Río Grande, and Pisungo formations, potentially distinguishing western magmatic arc (Western Cordillera) sediment sources from evolving eastern thrust-belt sources (Puna-Eastern Cordillera). In addition to growth stratal relationships and 40Ar/39Ar constraints, conglomerate clast compositions reflect distinct lithologic differences, constraining the activation of the Cianzo thrust and coeval movement on the reactivated Hornocal fault. Finally, U-Pb geochronological analyses of sandstone detrital zircon populations in conjunction with paleocurrent data and depositional facies patterns help distinguish localized sources from more distal sources west of the basin, revealing a systematic eastward advance of Eocene to Miocene fold-thrust deformation in the central Andes of northern Argentina.
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TWO-WAY TRAVELTIME ANALYSIS FOR SEISMIC RESERVOIR CHARACTERIZATION
Samik Sil, Ph.D.
University of Texas at Austin, May 2009
Supervisor: Mrinal K. Sen
157 pages, 88 references, 6 tables
Two-way traveltime (TWT) is one of the most important seismic attributes for reservoir characterization. Erroneous analysis of TWT can lead to incorrect estimates of velocity models resulting in improper structural interpretation of the subsurface. TWT analysis starts with the most fundamental step of seismic data processing, namely, Normal Moveout (NMO) correction. NMO correction is generally performed in the offset-time (X-t) domain, by fitting a hyperbolic curve to the observed traveltime corresponding to each reflection event. The performance of NMO correction depends on the quality of the data in the prestack domain and the underlying geology.
When ideal data sets are available (high signal to noise ratio), and underlying geology is simple (flat layers), the NMO correction can still be erroneous due to 1) its long offset non-hyperbolic behavior, and 2) due to the presence of seismic anisotropy. Even though in the X-t domain several equations have been developed to account for seismic anisotropy induced non-hyperbolic move out, they are prone to error, when multiple anisotropic and isotropic layers are present. The non-hyperbolic equations for moveout corrections are also approximate as they are some form of truncated Taylor series and can only estimate effective root mean square (rms) parameters for each reflection event.
In the plane wave (τ-p) domain, the estimation of layer parameters can be done using exact equation for delay-time free from the approximation errors present in the X-t domain. In this domain a layer striping approach can also be used to account for the presence of multiple anisotropic and isotropic layers. Thus it is lucrative to develop NMO correction equation in the τ-p domain for an anisotropic medium, which in its limiting case can be useful for the isotropic medium as well.
The simplest anisotropic media are Transversely Isotropic (TI) media which are also common in exploration seismology. One of the TI media, with a vertical axis of symmetry (VTI) shows non-azimuthal anisotropy whereas another TI medium, with a horizontal axis of symmetry (HTI) shows azimuthal anisotropy. Since quantifying VTI is easy (as it does not have azimuthal effect) most of the initial researches have focussed on VTI media. Satisfactory NMO correction equations are also available for the VTI media in the τ-p domain. In this thesis I have developed a τ-p domain NMO correction equation for the HTI media, which in its limiting cases can be used for VTI and isotropic media.
More complicated anisotropic medium than TI media is an orthorhombic medium. Orthorhombic media are common when two sets orthogonal vertical fractures sets are observed in the subsurface. Estimation of model parameters in such media from traveltime analyis is more complicated and no work in the τ-p domain for such media is reported before. To fill this gap, this thesis reports on the development of a τ-p domain NMO correction equation for the orthorhombic medium as well. In the limiting case this equation takes the form of a pervious τ-p domain TI media NMO correction equation.
For the purpose of subsurface parameter estimation based on traveltime, it is important to determine the presence of anisotropy in the data set. For that I developed a critical angle reflectometry scheme in the τ-p domain. This method analyzes critical slowness at each azimuth and relates it with the anisotropy parameters. Satisfactory critical slowness analysis for detecting anisotropy is presented in this thesis.
Even though most of the rocks are anisotropic ‘until proved otherwise’, data processing schemes commonly employed in the industry are based on isotropic assumption of the earth model. This can lead to large residuals in the NMO corrected traveltime. This residual traveltime can be used for anisotropic parameter estimation. In this thesis I present a case study from the Gulf of Mexico, where residual traveltime from seismic data and anisotropy parameter information from well logs are used with the help of geostatistics to generate fracture maps showing spatial variations of fracture orientation.
Finally I present a case study from the Gulf of Mexico, where estimation of structural uncertainty is made by combining traveltimes from seismic data, and well log derived marker depths in the time domain. I used a Markov-Bayes stochastic simulation to estimate structural uncertainty. Occurence of significant uncertainty in several parts of the subsurface model may be attributed to using erroneous velocity model, presence of faults and fractures in the subsurface, and ignoring seismic anisotropy during data processing.
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FACILITY PLANNING AND VALUE OF INFORMATION USING A TANK RESERVOIR MODEL: A CASE STUDY IN RESERVE UNCERTAINTY
Ashutosh Singh, MA
University of Texas at Austin, May 2010
Supervisor: Christopher J. Jablonowski
63 pages, 25 references, 9 tables
This thesis presents a methodology to incorporate reservoir uncertainties and estimate the loss in project value when facility planning decisions are based on erroneous estimates of input variables. We propose a tank model along with integrated asset development model to simulate the concept selection process. The model endogenizes drilling decisions and includes an option to expand. Key decision variables included in the model arc number of pre-drill wells, initial facility capacity and number of well slots. Comparison is made between project value derived under erroneous estimates for reserve size and under an alternate hypothesis. The results suggest loss in project value of up to 40% when reservoir estimates are erroneous. Moreover, both optimistic and pessimistic reserve estimates results in a loss in project value. However, loss in project value is bigger when reserve size is underestimated than when it is overestimated.
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KINEMATIC AND GEOMETRIC EVOLUTION OF THE BUCKSKIN-RAWHIDE METAMORPHIC CORE COMPLEX, WEST-CENTRAL ARIZONA
John Selwyn Singleton, Ph.D.
University of Texas at Austin, December 2011
Supervisor: Sharon Mosher
235 pages, 22 references, 9 tables, 4 loose maps
Reconstructing the structural evolution of metamorphic core complexes is critical to understanding how large-magnitude extension is accommodated in the middle to upper crust. This dissertation focuses on the Miocene geometric and kinematic evolution of the Buckskin-Rawhide metamorphic core complex in west-central Arizona, addressing controversial topics including the geometric development of mid-crustal shear zones, the formation of detachment fault corrugations, and the transition from detachment faulting to more distributed deformation.
Detailed microstructural data from mylonites in the lower plate of the Buckskin- Rawhide detachment fault indicate that early Miocene mylonitization was characterized by consistent top-NE-directed shear and ~450-500°C deformation temperatures that varied by =50°C across a distance of ~35 km in the extension direction. The relatively uniform deformation conditions and strain recorded in mylonitized ~22-21 Ma granitoids are incompatible with models in which the lower plate shear zone represents the down- dip continuation of a detachment fault. Instead, lower plate mylonites initiated as a subhorizontal shear zone that was captured and rapidly exhumed by a moderately to gently dipping detachment fault system.
Structural data and geologic mapping demonstrate that the prominent NE-trending Buckskin-Rawhide detachment fault corrugations are folds produced by extension- perpendicular (NW-SE) shortening during core complex extension. Dominant NE- directed slip on the detachment fault was progressively overprinted by NW- and SE- directed slip associated with corrugation folding. Orientation patterns of upper plate bedding across the corrugations are compatible with folding about a NE-trending axis. Extension-perpendicular shortening in the lower plate is recorded by synmylonitic constriction and folding. Upright m-scale and km-scale lower plate folds parallel the detachment fault corrugations and developed primarily by postmylonitic flexural slip that was coeval with detachment faulting. The total amount of NW-SE shortening across the lower plate is ~10%, but the amount of NW-SE shortening recorded by the younger detachment fault is only ~1%. The relatively late-stage development of corrugations in the Buckskin-Rawhide metamorphic core complex suggests that extension-perpendicular shortening was primarily driven by a reduction of vertical stresses through crustal thinning and tectonic denudation.
Brittle fault data document the transition from large-magnitude, NE-directed extension to distributed E-W extension and right-lateral faulting. Following exhumation to brittle conditions, lower plate mylonites were extended up to ~20-30% by NE-dipping, syndetachment normal faults. Towards the end of detachment faulting, the extension direction rotated clockwise, and some portions of the Buckskin detachment fault record a transition from dominant top-NE slip to ENE- and E-directed slip. After detachment faulting ceased, E-W extension was accommodated primarily by steeply NE-dipping, right-lateral and oblique right-lateral-normal faults. The cumulative amount of right- lateral shear across the core complex is probably 7-9 km, which is the amount needed to restore the topographic trend of lower plate corrugations into alignment with the dominant extension direction. Postdetachment right-lateral/transtensional faulting across the Buckskin-Rawhide metamorphic core complex reflects the increasing influence of the Pacific-North American transform plate boundary towards the end of the middle Miocene.
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GEOMETRY AND NATURE OF MODERN AND ANCIENT MASS TRANSPORT DEPOSITS WORLDWIDE
Kadira Analisa Singh, MS
University of Texas at Austin, May 2010
Co-Supervisor: Lesli Wood
Co-Supervisor: William Fisher
140 pages, 90 references, 3 tables
Mass transport deposits form a significant portion of the rock record in both modern and ancient basins. Their geometry, composition, distribution and genesis are poorly understood, making it difficult to predict anything about these deposits in assessing subsurface basin stratigraphy or modern seafloor hazards. A tremendous effort has been made in the last few years to characterize and better understand seafloor failures in numerous margins of the world. These mass failures have triggered the interests of geologists, particularly in the oil and gas industry, as they can form prominent seals and reservoirs. To increase our knowledge base of mass transport deposits (MTDs), the characteristics of 259 siliciclastic deposits worldwide, were analyzed in terms of their volume, area, length, thickness, lithology, and tectonic settings. In some instances, MTDs were geo-referenced and digitized into ArcGIS and their dimensions were calculated. These data reveal several interesting points and suggest a number of statistically significant predictive relationships. Sand-rich mass transport deposits show a propensity to be short and thick. Muddy MTDs show a propensity to be longer and thinner. The highest number and largest volume of clastic mass transport deposits occur along passive margins. These mega-MTDs are typically muddy with lengths up to 800 km and volumes up to 5000 km3. Sandy and gravelly Quaternary-age MTDs show maximum lengths of less than 300 km and with volumes less than 2000 km3. Pre-Quaternary MTDs are systematically under-documented in literature, but known occurrences are found in passive, active and convergent margins. The largest (30,000 to 40,000 km2) occur along the older Tertiary margin of West Africa. To date, 41 separate mass transport deposits composed dominantly of carbonate material have been identified in literature. The most extensive and voluminous (7000 km3) carbonate mass transport deposits occur in the Citronens Fjord, Offshore Greenland. They are 200 m thick, Silurian-age mega-breccias that were deposited in a convergent margin setting. On comparison carbonate MTDs tend to show longer flows with coarser grain sizes, while clastics show coarser grained deposits to be of more limited length. The Mad Dog area, Gulf of Mexico is a region of active salt tectonics and mass transport processes. Consequently, it was selected to form a focus study area to test the relationships developed during this project. MTDs in this region were grouped into four main types based on their size, geomorphology and internal structure. Their geometries indicate they are comparable to MTDs found offshore Oregon and New Jersey and are most likely muddy in nature.
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SURFACE ROUGHNESS OF NATURAL ROCK FRACTURES: IMPLICATIONS FOR PREDICTION OF FLUID FLOW
Donald Timothy Slottke, Ph.D.
University of Texas at Austin, May 2010
Supervisor: John M. Sharp, Jr.
234 pages, 60 references, 20 tables
Where open, connected fractures are present, they dominate both fluid flow and transport of solutes, but the prediction of hydraulic and transport properties a priori has proven exceedingly difficult. A major challenge in predicting solute transport in fractured media is describing the physical characteristics of a representative surface that is appropriate to modeling. Fracture aperture, roughness, and channeling characteristics are important to predict flow and transport in hard rock terrains. In areas with little soil cover, fracture mapping can indicate areas or directions of greater permeability but not the magnitudes. Both cover and complex geology can limit mapping. Hand samples are generally available and upscaling from their properties would be highly beneficial. Assessing the impact of roughness on field-scale fluid flow through fractured media from samples of natural fractures on the order of 100cm2 assumes a relationship between fracture morphology and discharge is either scale invariant or smoothly transformable. It has been suggested that the length scale that surface roughness significantly contributes to the discharge falls within the size of a typical hand sample, but few data exist to support extension of small-scale relationships to larger scales. I analyze the results of flow tests on a single fracture through a 60 x 30cm block of rhyolitic tuff. The results are compared with relationships of smaller samples in a similar tuffs and granites. The data are processed to yield regularly gridded surface elevations. Describing roughness as a ratio of surface area to footprint, variances of the roughnesses of surface covering equivalently sized square samples are plotted against sample size to determine if a representative surface exists. For specimens of fractures measuring up to 25 x 29cm, a 3.2 x 3.2cm sample of granite with an iron oxide/clay fracture skin yields a reasonable expression of the roughness of the entire surface. The number of data points included in a sample of this size transcends skin type, composition and grain/crystal size. The results suggest that the unmodified cubic law is valid for the range of gradients expected in the field using the geometric mean of areal aperture data to estimate hydraulic aperture. The data also indicate that fracture aperture is not well predicted by single aperture measurements or even by averaging along a particular scan line; three-dimensional laboratory analysis and/or field testing are required. There may be a suitable scale of data for upscaling fracture roughness on the order of 10cm2. However, due to mismatch between top and bottom surfaces inherent in natural fractures, aperture samples are not consistent across the specimen and cannot be scaled. Upscaling of other factors, such as flow channeling, remain to be tested.
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SYSTEMATICS AND EVOLUTION OF EXTINCT AND EXTANT ALCIDAE (AVES, CHARADRIIFORMES) : COMBINED PHYLOGENETIC ANALYSES, DIVERGENCE ESTIMATION, AND PALEOCLIMATIC INTERACTIONS
Neil Adam Smith, Ph.D.
University of Texas at Austin, August 2011
Supervisor: Julia A. Clarke
748 pages, 486 references, 41 tables
Although the ecological interactions and ethology of the wing-propelled diving seabirds known as the Alcidae (Aves, Charadriiformes) have been intensively studied, systematic studies of the clade have been overwhelmingly limited to extant taxa. Alcidae have the richest fossil record among Charadriiformes, with specimens representing more than 35 million years of evolutionary history. Morphometric and apomorphy-based taxonomic revision of previously named extinct alcids along with description of new species of extinct alcids facilitated refined estimates of species richness. Combined phylogenetic analyses of morphological and molecular sequence data including alcid fossils elucidated the poorly understood evolutionary history of the clade. Divergence estimation analysis for Charadriiformes placed previously hypothesized episodes of alcid radiation and extinction in context with proposed paleoclimatic drivers of alcid evolution.
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EVOLUTION OF PLINIAN MAGMAS FROM POPOCATÉPETL VOLCANO, MÉXICO
Giovanni Sosa Ceballos, Ph.D.
University of Texas at Austin, May 2010
Supervisor: James E. Gardner
421 pages, 101 references, 10 tables
Fractional crystallization, magma mixing, assimilation of continental crust, and how those processes modify volatile budgets, control the evolution of magma. As a consequence, the understanding of these processes, their magnitudes, and timescales is critical for interpreting ancient magma systems, their eruptions, and the potential future volcanic activity. In this dissertation I present the results of three projects. The first explores how magmatic processes affect magma reservoirs and eruption dynamics. The second explores where in the storage system and how often these processes occur. The third explores how volatile budgets are modified by processes such as crystallization, mixing, and assimilation.
Volcán Popocatépetl (central México) erupted ~14100 14C yr BP producing the Tutti Frutti Plinian Eruption (TFPE). The eruption tapped two different silicic magmas that mixed just prior and during the eruption. The influx of mass and volatiles generated during the mixing of both magmas overpressured the reservoir, which was weakened at the top. The weakened reservoir relaxed while magma was tapped and collapsed to form a caldera at the surface.
Although it is known that fractional crystallization, mixing, and assimilation can greatly modify magmas, the frequency and intensity of these events is not known. I investigated the magmatic processes responsible for the evolution of magmas erupted during five Plinian events of Popocatépetl volcano. Results show that during the last 23 ky magma was stored in two different zones, and was variably modified by replenishments of mafic magma. Interestingly, little evidence for large mafic inputs triggering explosive eruptions was found.
Each of these processes alters the abundances of volatiles and introduces different types of volatiles to the system. Hence, the volatile budget of magma can have a rich and complex history. To investigate how volatile budgets evolve in active magma systems, I analyzed the abundances of volatiles (H2O, CO2, F, Cl, and S) in numerous glass inclusions trapped in phenocrysts. Results show that the magmas that produced the last five Plinian eruptions at Popocatépetl volcano evolved by crystallization and magma mixing, assimilation of the local carbonate basement is not chemically appreciable. Mixing with mafic magmas added substantial CO2 and S to the system, dewatered the magma, yet produced little change in the F contents of the magmas.
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EFFECTS OF DAM-INDUCED DAILY RIVER STAGE FLUCTUATIONS AND SEDIMENTARY ARCHITECTURE OF A LARGE GRAVEL BAR ON GROUNDWATER FLOWPATHS
Blair Avant Stanley, MSGeoSci
University of Texas at Austin, August 2009
Supervisor: Meinhard Bayani Cardenas
89 pages, 54 references, 10 tables
Dam-controlled river stage fluctuations alter groundwater-surface water connectivity between persistent gravel bars and rivers. Hydraulic gradients in the hyporheic zone, the transition zone between a river and an aquifer, change as river stage fluctuates, thus affecting the magnitude and direction of water flow within riverbanks, and potentially modifying important biogeochemical and ecological processes. However, limited research has been conducted on river islands subjected to regular and marked changes in stage. A large gravel bar with an established riparian forest, located in the Colorado River (Austin, TX), is subjected to daily storage and release of water, and river stage variations over one meter. Questions driving this project are: (1) How do regulated stage fluctuations affect transient flow patterns in the gravel bar? (2) What is the sedimentary architecture of the island and how does this control surface water-groundwater exchange? And (3) Is the hydraulic conductivity distribution in the island affecting the surface water-groundwater exchanges flow paths in the bar? Groundwater dynamics and sedimentary architecture of this large gravel bar were investigated by mapping the water table and groundwater flow paths, mapping sedimentary units, and permeability measurements of the sediment. Piezometer nests were installed and instrumented with logging pressure-transducers to monitor the evolution of head distributions and groundwater flow paths through several cycles of dam release and storage, and correlated to river discharge from gauging stations upstream of the site and downstream of the dam. Sediment samples were collected during piezometer installation; hydraulic conductivity values were obtained from grain-size analyses of the samples. Results show that hydraulic head within the island closely tracks the river stage associated with dam release. Water table variations permeated throughout the island, but decreased in intensity with distance from the bank. Dam operations have drastically altered groundwater-surface water connectivity between the Colorado River and the riparian aquifer at Hornsby Bend Island by pumping water in and out of the aquifer during dam release and storage cycles respectively. The pronounced surface water-groundwater interactions also affected groundwater temperatures in the island tens of meters from the bank, indicative of strong advective heat transport.
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THE LITTLE BUCKSKIN MOUNTAINS: A FOOTWALL CORRUGATION WITHIN THE BUCKSKIN-RAWHIDE METAMORPHIC CORE COMPLEX, WEST CENTRAL ARIZONA
Evan Douglas Strickland, B.S.
University of Texas at Austin, May 2010
Supervisor: Mark Cloos
63 pages, 16 references
Metamorphic core complexes are features of large magnitude [10’s of km] crustal extension. Extension is accommodated by a regional-scale, low-angle, normal offset detachment fault. The detachment faults and footwalls of most core complexes are undulating, and several models have been proposed to explain the origin of these corrugations. The Little Buckskin Mountains are an antiformal footwall exposure that is a corrugation in the Buckskin-Rawhide metamorphic core complex. Mylonitic foliations define a subhorizontal NE-SW trending axis that is parallel to the regional extension direction. Across the antiform axis mylonitic stretching lineations and epidote veins have different orientations. Rotating the limbs of the antiform to horizontal reorients the lineations and epidote veins on either side of the antiform axis into parallelism. This indicates the ductile stretching lineations and brittle epidote veins formed before the footwall block was arched to create the antiform. Meter-scale upright folds, some of which record evidence of forming from flexural slip along the mylonitic foliation, are interpreted as parasitic folds to the antiform. The Little Buckskin Mountains antiform is interpreted as a late-stage fold that resulted from ~10% horizontal, extension-perpendicular shortening within west central Arizona.
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THE ORIGIN AND PROPERTIES OF MASS TRANSPORT DEPOSITS URSA BASIN, GULF OF MEXICO
Hilary Elizabeth Strong, MSGeoSci
University of Texas at Austin, December 2009
Supervisor: Peter B Flemings
77 pages, 53 references, 9 tables
Uniaxial consolidation experiments on Mass Transport Deposit (MTD) and non-MTD core samples from Ursa Basin, Gulf of Mexico, show MTDs have a lower porosity at a given effective stress compared to adjacent non-MTD sediments; a behavior observed in additional experiments on lab remolded Ursa core and resedimented Boston Blue Clay (BBC). I hypothesize debris flow action remolded the sediment: removing its stress history through shearing action, resulting in dense sediments at shallow depth. I supplement testing this hypothesis through lab remolding of BBC (in addition to Ursa clay) due to the greater availability and knowledge of this material. Ursa MTDs record multiple submarine slope failure events within the upper 200 meters below sea floor (mbsf); the most prominent is labeled MTD-2. MTDs have lower porosity and higher bulk density than surrounding, non-MTD, sediment. Porosity Φ is 52% at 125mbsf – immediately below MTD-2; whereas Φ is 46% at 115mbsf – within MTD-2. Comparison of non-MTD samples to MTD-2 samples, and intact to remolded samples, shows a decrease in sediment compressibility (Cc) within the MTD-2 and remolded sediments. Permeability within Ursa mudstones also declines with porosity according to: log (k) = AΦ - B. Permeability is slightly higher within MTD-2; however grain size analysis indicates lower clay content in MTD-2 versus the non-MTDs. Pre-consolidation stress interpretations from the experiments show a linear trend in both MTD and non-MTD sediments, indicating both geologic units depict the same pore pressure profile. Remolding via debris flow explains the origin of MTDs at Ursa and governs the evolution of this geologic unit to its dense, highly consolidated, state today. At some point, slope failure triggered movement of the sediment down slope in form of a debris flow. The shearing action of the debris flow weakened the sediment, reducing its ability to support the overburden. As consolidation resumed, the remolded sediment followed a new, less steep, Cc curve. Within the geologic record, a distinctive dense, shallow unit is preserved; evidence for historical slope failure.
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COMPARISON OF FLUID PREDICTION SUCCESS BETWEEN AVO AND BRIGHT SPOT TECHNIQUES IN THE MARCO POLO FIELD, THE GULF OF MEXICO
Krongrath Suwannasri, B.S.
University of Texas at Austin, May 2011
Supervisor: Robert Tatham
45 pages, 10 references, 4 tables
Bright spot amplitude anomalies in exploration seismic data are common indicators of natural gas; however, an interpretation based purely on these amplitude anomalies is often a false I indicator of natural gas. A data set from the Marco Polo field, the Gulf of Mexico, demonstrates this. A discovery well was drilled into a sequence of bright spot anomalies that indeed gas-I saturated sands. This suggested that other bright spots in the seismic section also corresponded to gas sands and that non-bright spots were brine-saturated sands. Nine development wells were later drilled into those bright spots, but not all of them were gas sands and not all of non-bright : spots were brine saturated sands. This study utilized Gassmann fluid substitution and three i seismic amplitude versus offset (AVO) techniques (intercept and gradient, elastic impedance, and Lambda-Mu-Rho) as a comparison to using only bright spots for fluid-type prediction away from the discovery well in the purpose of calibration. This method used borehole information only from the discovery well. Forward models for the three techniques were created from the ; well-log information in order to predict differences in the modeled attributes between gas- and brine-saturated scenarios. Pre-stack seismic data were inverted for intercept and gradient j attributes, elastic impedance (EI) volumes, and Lambda-Mu-Rho (LMR) volumes. These volumes were compared to the forward models to predict gas- and brine-saturated locations. The prediction results were evaluated with information from the nine development wells. The intercept and gradient, elastic impedance, and LMR techniques yielded correct predictions of 52%, 61%, and 70%, respectively, of the observed sands. The traditional bright spot method yielded only 45% correct fluid prediction. In conclusion, the pre-stack AVO techniques provided a better fluid prediction than relying solely on the post-stack bright spots alone. Furthermore, the prediction results improved as the computational intensity of the inversion increased from the intercept and gradient, to the elastic impedance, and to the LMR technique.
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HEAT TRANSPORT AND TRACING WITHIN THE HYPORHEIC ZONE OF A POOL-RIFFLE-POOL SEQUENCE
Travis Eric Swanson, MS GeoSci
University of Texas at Austin, May 2010
Supervisor: Meinhard Bayani Cardenas
95 pages, 46 references, 1 table
Hyporheic water is thought to infiltrate at the head of a riffle which in turn is complemented by upwelling back to the stream at the tail of the riffle in a pool-riffle-pool (PRP) sequence. Heat tracing is a potentially useful method to characterize these hyporheic flow paths and quantify associated fluxes. Temperature was monitored within a PRP sequence for several days. Temperature in the hyporheic zone reflected the diel temperature change in the river but not uniformly. The observed thermal pattern exhibited deeper penetration of thermal oscillations below the head pool and shallower penetration below the tail pool. This pattern is consistent with the conceptual model of hyporheic exchange over a PRP sequence. One-dimensional analytical heat transport models were used at different points below the PRP sequence to estimate distributed vertical fluid fluxes. The calculated fluxes exhibit a trend that follows the expected distribution for a PRP sequence but modified for a losing stream. Deviation of both magnitude and distribution of fluxes from the conceptual ‘downwelling-to-upwelling’ model is partly due to the dominantly losing conditions at the study site but the trends are consistent with a losing stream undergoing hyporheic exchange. Violation of the assumptions in the analytical models most likely adds error to flux estimates. For this study, flux estimation methods using a temperature time series amplitude analysis more closely matched field measurements than phase methods.
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BASALTIC VOLCANISM : DEEP MANTLE RECYCLING, PLINIAN ERUPTIONS, AND COOLING-INDUCED CRYSTALLIZATION
Lindsay Ann Szramek, Ph.D
University of Texas at Austin, August 2010
Supervisors: James E Gardner and John C. Lassiter
314 pages, 109 references, 17 tables
Mafic magma is the most common magma erupted at the surface of the earth. It is generated from partial melting of the mantle, which has been subdivided into end-members based on unique geochemical signatures. One reason these end members, or heterogeneities, exist is subduction of lithospheric plates back into the mantle. The amount of elements, such as Cl and K, removed during subduction and recycled into the deep mantle, is poorly constrained. Additionally, the amount of volatiles, such as Cl, that are recycled into the deep mantle will strongly affect the behavior of the system. I have looked at Cl and K in HIMU source melts to see how it varies. Cl/Nb and K/Nb suggest that elevated Cl/K ratios are the result of depletion of K rather than increased Cl recycled into the deep mantle.
After the mantle has partially melted and mafic melt has migrated to the surface, it usually erupts effusively or with low explosivity because of its low viscosity, but it is possible for larger eruptions to occur. These larger, Plinian eruptions, are not well understood in mafic systems. It is generally thought that basalt has a viscosity that is too low to allow for such an eruption to occur. Plinian eruptions require fragmentation to occur, which means the melt must undergo brittle failure. This may occur if the melt ascends rapidly enough to allow pressure to build in bubbles without the bubbles expanding. To test this, I have done decompression experiments to try to bracket the ascent rate for two Plinian eruptions. One eruption has a fast ascent, faster than those seen in more silicic melts, whereas the other eruption is unable to be reproduced in the lab, however it began with a increased viscosity in the partly crystallized magma.
After fragmentation and eruption, it is generally thought that tephra do not continue to crystallize. We have found that crystallinity increases from rim to core in two basaltic pumice. Textural data along with a cooling model has allowed us to estimate growth rates in a natural system, which are similar to experimental data.
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TECTONOSTRATIGRAPHIC EVOLUTION OF THE NORTHEASTERN MATURIN FORELAND BASIN, VENEZUELA
Gustavo A. Taboada, M.S. Geo. Sci.
University of Texas at Austin, August 2009
Supervisors: Paul Mann and William L. Fisher
97 pages, 72 references, 3 tables
The study uses subsidence analysis of three deep wells to basement combined with sequence stratigraphic mapping to show that a 85,000 km2 area of the Eastern Venezuelan foreland basin in the region of the Orinoco Delta underwent three main stages of foreland-related subsidence that followed a protracted Cretaceous - late Oligocene period of precollisional, passive margin formation. Phase 1 consists of increased foreland basin subsidence in the late Oligocene to middle Miocene (23 - 13 Ma) at average sedimentation rates of 0.14 mm/yr. Clastic rocks of Phase 1 include the Freites Formation, a 1.2 km-thick section of greenish-gray fissile shale and shaly sandstone deposited in shallow marine- neritic environments. Seismic facies show progradation of Phase 1 clastic rocks as a wedge from the NE and NNE. Clastic rocks deposited during the accelerated Phase 2 in the middle to late Miocene (13 -11 Ma at sedimentation rates of 1.45 mm/yr) include the La Pica Formation, a 2.7 km-thick section of gray silt and fine-grained sandstone deposited in shallow marine/coastal proximal environments. Seismic facies show progradation of Phase 2 clastic rocks as a wedge to the northeast. Phase 3 consists of decelerating foreland basin subsidence in the period of late Miocene-mid Pliocene (11-6 Ma at average sedimentation rates of 0.86 mm/yr). Sedimentary rocks deposited during this period include the Las Piedras Formation, a 1.45 km-thick section of sandstone, carbonaceous siltstone and shale deposited in deltaic environments. Seismic facies show a progradation of Phase 3 clastic rocks as a wedge to the northeast and east-northeast. Deeper marine environments and more rapid subsidence rates of Phases 1 and 2 are interpreted as an underfilled foreland basin controlled by active thrusting along the Serrania del Interior at the northern flank of the basin. Deltaic environments and slower rates of Phase 3 are interpreted as an overfilled foreland related to rapid seaward progradation of the Orinoco Delta and its filling of the former, dynamically- maintained interior seaway. Paleogeographic maps constrained by wells and seismic lines show a large regression of the Orinoco River towards the west across the Columbus basin and Eastern Venezuelan basin during the late Miocene and the Paleocene. In this foreland basin setting, the effects of thrust-related tectonic subsidence and early deposition of the Orinoco Delta play a larger role in the early Miocene-Pleistocene sequences than eustatic effects.
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P-T-T PATHS AND DEFORMATION OF BLUESCHIST AND ASSOCIATED GRAPHITE-SCHIST BLOCKS FROM THE FRANCISCAN MÉLANGE, SAN SIMEON, CALIFORNIA
Estibalitz Ukar, Ph.D.
University of Texas at Austin, May 2010
Supervisor: Mark Cloos
1218 pages, 224 references, 16 tables
The Franciscan Complex forms the structurally complicated, locally chaotic basement of the Northern and Central California and southwestern Oregon Coast Ranges. It is an accretionary wedge formed during the Late-Jurassic-Tertiary subduction along the west coast of North America.
In northern California, the Franciscan is subdivided into three belts, the Western, Central, and Coastal belts, which show a zonation in age, metamorphic “grade”, and structural style. Franciscan mélanges are present in the Central belt, as well as the Diablo Range --a tectonic window within the structurally overlying Great Valley Group--, and the Nacimiento Block, where the study area is located.
One of the best exposures of Franciscan mélange, where contact relationships between blocks and matrix can be observed, crops out along 6 km of seacliffs near San Simeon. Boudinaged blocks of graywacke, greenstone, chert, and much rarer blueschist and graphite-schist are dispersed in the shale matrix. Block sizes range from 10 cm to 15 m. The discovery of interlayered blueschist and graphite-schists, and the presence of lawsonite in some graphite-schists demonstrate that these two lithologies were metamorphosed together. Graphite-schist blocks in the Franciscan have not been reported prior to this study.
Two main mineral assemblages were recognized among the studied 34 mafic blueschist blocks: 1) Lws + Na-amp + Pmp + Phe + Ttn + Chl recrystallized at ~5 kbar and 200-250°C, and 2) Lws + Na-amp + Pmp + Phe + Ttn + Ep + Chl, which recrystallized under slightly higher temperatures but similar pressures (300-350°C, at 5 kbar). A pre-blueschist facies metamorphic event under greenschist facies conditions is recorded by calcic cores overprinted by Na-amp rims in about half of the blocks. Sodic amphibole rims with a higher Fe3+ content probably developed due to the breakdown of epidote during a decrease in T. These mafic blueschists followed a counterclockwise P-T path.
Remnants of “actinolitic rinds”, which are reaction zones formed when the blocks were in contact with serpentine, were found associated with nine of the studied mafic blueschist blocks. Such rinds were thought to be unique to better-studied Franciscan high-T blocks.
Graphite-schist blocks (30 studied) contain Qtz + Phen + Ab + Gr, and are of two types. One type has relict sedimentary textures with a weak foliation defined by graphite and pressure solution seams. The other type has a compositional layering with layers containing well recrystallized quartz. Nine of these blocks also contain lawsonite within the more graphitic layers.
The geochemistry of the blueschist blocks indicates that they were derived from the MORB-like oceanic crust, and seamounts underplated during the initiation of subduction. The mainly mafic protolith contained a small volume of interlayered sediment, as indicated by the presence of associated metasedimentary graphite-schists. Blueschist facies conditions were attained at the bottom of the overriding plate during the initial states of Franciscan subduction (150-155 Ma). Mafic material continued to be underplated, and low-T dynamic blueschist-facies metamorphism continued to form until at least ~137 Ma.
A model is proposed in which exhumation was facilitated by normal faulting near the surface driven by gravitational collapse driven by decrease in subduction plate dip around 80 Ma that is known to have caused the Laramide orogeny. During this time, blueschist and graphite-schist blocks were plucked from the bottom of the hanging wall, incorporated into the shale- and water-rich shear zone at the plate interface, and exhumed during the upward flow of mélange driven by the movement of the downgoing plate. Blocks were extended and boudinaged, and metasomatically altered in the cataclastic zones that developed along necks and margins of the blocks during upwelling and the dewatering that led to final compaction near the surface.
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STRUCTURAL CONTROLS ON CO2 LEAKAGE AND DIAGENESIS IN A NATURAL LONG-TERM CARBON SEQUESTRATION ANALOGUE: LITTLE GRAND WASH FAULT, UTAH
Estibalitz Ukar, Ph.D.
University of Texas at Austin, August 2011
Supervisors: Peter Eichhubl, Tip Meckel, and Stephen E. Laubach
437 pages, 190 references, 21 tables
The Little Grand Wash normal fault near Green River, eastern Utah, hosts a series of naturally occurring CO2 seeps in the form of active and extinct CO2-charged springs distributed along the fault zone. I have studied the association of fault structure with CO2-related alteration as an analogue for the long-term (1,000- to 10,000-year) effects of leakage through faults in CO2 sequestration reservoirs. Structure and alteration in a portion of the Little Grand Wash fault zone were mapped at a 1:700 scale in order to determine the association of faulting with CO2-related diagenesis. I combined structural and diagenetic mapping were combined with laboratory analyses of mineralogical, isotopic and textural changes in order to assess controls on the migration of CO2 traveling up the fault and its effects on the fault itself.
The fault zone is 200 m wide at its widest and contains 4–5 major subparallel fault segments that form multiple soft- and hard-linked relay ramps. The area includes a travertine deposit and related sandstone alteration: outcrop-visible coloration, porosity-occluding calcite cement and veins occasionally so abundant that they obliterate the rock fabric. Structural mapping shows that the travertine is located at an intersection of major fault segments constituting the hard link of a 450-meter-long relay ramp. Sandstone alteration is confirmed to be related to the CO2 seep by mapping its distribution, which shows a decrease in concentration away from the travertine, and by the unique isotopic signature of calcite cement near the travertine. At distances greater than 25 m from the travertine intense alteration disappears, though scattered fault-subparallel veins and patchy, burial-related calcite cement remain. Intense alteration is limited to major fault overlaps and does not permeate the fault zone along its entire length, nor does it extend outside the zone. This indicates that rising CO2-laden fluids do not flow uniformly through the entire fault zone, but that vertical flow is channeled at fault intersections.
In thin section, porosity near the travertine has been extensively or completely occluded by calcite cement. Permeability in some conduit samples is less than 1 mD, three or four orders of magnitude lower than sandstone away from the travertine. In active CO2 conduits, such reduction in porosity and permeability would occlude the preferred flow conduit and ultimately restrict upward flow of CO2-charged water.
X-ray diffraction detects small amounts of goethite and hematite and a decrease in chlorite-smectite in altered conduit sandstones. Calcite is abundant, but many authigenic minerals predicted by geochemical models of CO2 influx into sandstone reservoirs are not observed, including kaolinite, aragonite, dolomite, siderite, ankerite or dawsonite. This difference between observed and predicted mineral occurrence likely results from differences in mineral kinetics between natural and laboratory systems.
Prediction of leakage risk based on fault geometry improves the ability to assess the suitability of potential carbon sequestration reservoirs, many of which will be faulted. The point seep nature of leakage through a fault zone limits the amount of CO2 that can escape over time and also enables targeted surface monitoring for CO2 escape into the atmosphere—both critical for ensuring the effectiveness of injection projects and earning the trust necessary for carbon sequestration to gain public acceptance. The point seep nature of leakage also accelerates the rate at which conduits may seal through mineralization, since precipitation from a large volume of fluid is focused in a narrow conduit. The presence of multiple fossil and active seep locations along the Little Grand Wash fault, active at different times in the geologic past, indicates that cementation may be effective in sealing single conduits but that fault systems with complex geometry such as Little Grand Wash may continue to leak for a long period of time.
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MULTICOMPONENT SEISMIC INTERPRETATION OF TIGHT GAS SANDSTONES WITHIN THE BOSSIER FORMATION AT THE TENNESSEE COLONY FIELD, ANDERSON COUNTY, TEXAS.
Diego Alexander Valentin Navarrete, MSGeoSci
University of Texas at Austin, August 2010
Supervisor: Robert H. Tatham
111 pages, 56 references, 4 tables
The central part of the East Texas Basin contains the Tennessee Colony field and its Upper Jurassic tight gas sandstones in the upper part of Bossier Formation. Exploration and development activities in this area provided a scenario to successfully apply a multicomponent interpretation for lithology discrimination in deep targets where the vertical and lateral resolution, low impedance contrast between the reservoir sandstones and the encasing shales and the noise of the seismic data limited the application of P-P wave seismic data as reliable indicator of lateral variations of the rock properties within the Bossier Formation.
The present study integrates the petrophysical analysis of 11 wells (5 of them with sonic and dipole sonic logs at the reservoir level), structural interpretation of a 186.5 km2 (72 miles2) P-P wave seismic data, correlation of the P-P and P-SV wave seismic data and the multicomponent interpretation of a 23.3 km2 (9 miles2) mode converted P-SV wave seismic data in order to infer the distribution of the reservoir sandstones within the Bossier Formation. This integration proved to be a powerful procedure in order to understand and validate the multicomponent-seismic interpretation of the distribution of the reservoir sands.
At the Tennessee Colony field, the Bossier Formation (Upper Jurassic) can be divided in two members. First, the Lower one is composed of shale and some silt and has low P- and S-wave velocities and high densities (3750 m/s, 2304 m/s and 2.66 g/cc respectively). Second, the Upper part is composed of silts and shales with higher P- and S-wave velocities and densities (4420 m/s, 2591 m/s and 2.67 g/cc respectively). When present, the reservoir sandstones, located in the Upper part and deposited by turbiditic flows in submarine slope and basin environments, are characterized by having higher P- and S-wave velocities (4770 m/s and 3057 m/s) and lower densities (2.54 g/cc) than the encasing lithology.
Despite the low lateral and vertical resolution of P-P and P-SV seismic data and limited correlation between the interval Vp/Vs values in large intervals and the net to gross values calculated from the well logs at the well location, the Vp/Vs ratio map extracted from the joint interpretation of P-P and P-SV seismic data shows that relative and major decreases in the Vp/Vs ratio reflect a local N-S trend in the deposition of the turbiditic sandstone that matches with the local trend interpreted from the net sand map generated from the well logs. Indeed one of the best wells in terms of thickness of the reservoir sandstones in the field matches with one of the lowest Vp/Vs areas.
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Bryce Hedrick Wagner III, Ph.D.
University of Texas at Austin, May 2010
Supervisors: Martin Jackson and Mark Cloos
218 pages, 214 references, 3 tables
Salt can be removed by viscous flow and dissolution to form a salt weld. A complete weld forms when salt is completely removed by these processes. Where salt removal is incomplete, a partial weld forms. Though welds are frequently mentioned in the literature, the details of weld formation and the properties of salt welds are poorly understood.
In Chapter 1, I use analytical and numerical models to quantify the role of viscous flow during salt welding. Where salt flow is limited by boundary drag against the salt contacts, evacuation is slow and up to ~50 m of salt will be left behind in a partial weld. Where salt flow is laterally unrestricted, a vanishingly thin (« 1 m) smear of salt will remain. I conclude that layer-parallel wall rock translation or dissolution must act to remove any remnant salt to create a complete weld.
In Chapter 2, I characterize partial welds containing halite and anhydrite on reflection seismic data by treating welds as thin beds. Below the temporal resolution of reflection seismic data, typically ~25-50 m for modern surveys with peak frequencies of ~10-30 Hz, reflections from the upper and lower evaporite contacts converge and interfere to form a single composite reflection. Thus, partial and complete welds are typically indistinguishable using travel-time differences alone. I then use amplitude information from synthetics and seismic examples to estimate remnant evaporite thickness.
In Chapter 3, I investigate fluid flow near and through salt welds. I conclude dissolution during boundary flow can remove up to a few meters of salt per million years. Though dissolution plays a volumetrically insignificant but important role in weld formation, as runaway dissolution can create pathways for focused cross-weld migration of subsurface fluids. I identify features that influence cross-weld migration of subsurface fluids and then develop an empirical relationship between weld geometry and the tendency seal or leak hydrocarbons. I find that in the Campos Basin, offshore Brazil, salt welds containing remnant evaporites thinner than ~50 m that are broader than ~25 km2 in area are likely to leak.
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WATER POLICY INFORMATICS : A TOPIC AND TIME SERIES ANALYSIS OF THE TEXAS STATE WATER PLANS
Jenifer Elizabeth Wehner, MA
University of Texas at Austin, May 2011
Supervisor: Suzanne Pierce
The disciplines of informatics and information visualization have developed in response to societal needs to find new insight in complex datasets and have been enabled by technological advancements. Joint application of these fields can demonstrate themes and connections that are otherwise not apparent. Methodological approaches, such as direct network analysis, can be applied to policy documents to determine if action or policy recommendations match the goals or objectives stated in the within the same documents. Informatics and information visualization can also be used to analyze changes of themes found within the documents over time. This paper seeks to leverage informatics and information visualization methodologies as a novel approach to policy analysis. In particular, directed network and time burst techniques are used to analyze water management policy documents for the State of Texas. The congruency between the stated goals or objectives and recommendations sections is evaluated at a topical level within each planning document and possible changes in important water policy concepts over time are highlighted by comparing among multiple planning documents. Although there limitations to the process at the time of publication due to the newness of the software utilized, this paper demonstrates that the products still lead to unique and insightful conclusions.
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PARTITIONING SAND TRANSPORT BETWEEN CHANNELS OF A DEEP RIVER CHANNEL BIFURCATION: IMPLICATIONS FOR RIVER DIVERSION STRUCTURES AND LAND BUILDING IN SOUTHERN LOUISIANA
Spencer Whitman, B.S. Hydrogeology/Environmental Geology
University of Texas at Austin, May 2010
Supervisor: David Mohrig
35 pages, 14 references, 1 table
Man-made diversion structures that cut through the levees of the Mississippi River act as channel bifurcations, delivering water and sediment to an otherwise disconnected wetland environment. In this study, the role of diversion depth in controlling the amount of sand that exits from the primary channel during river flooding is examined. We follow the sand fraction because new land built by active sub-deltas of the Mississippi River delta is predominately composed of sand rather than mud. Sand transport is not evenly distributed from the channel bottom to the water surface in large rivers. The highest concentrations of moving sand are located near the bed. This suggests that diversions dug to depths tapping the lowermost portion of the water column might export considerably more sand to the neighboring overbank regions for land building purposes. In order to explore the importance of deep diversions for land building we measured properties of the Atchafalaya River - Grand Lake bifurcation near Morgan City, LA, during high discharge in May, 2009. Grand Lake is the entrance point to the Wax Lake outlet channel and the Wax Lake delta. Persistent growth of this delta over the past 30 years highlights the successful land-building properties of this diversion. Bathymetry defining the geometry of this bifurcation, as well as measurements of flow and sediment transport in its Atchafalaya and Grand Lake branches is used to illustrate the effectiveness of a relatively deep diversion for land building. This case study can be used to evaluate the potential of other river diversions as conduits delivering sediment to neighboring wetlands for rebuilding the Mississippi River delta.
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A RE-EVALUATION OF CRINOID MORPHOLOGY AND PROPOSED RELATIONSHIP OF CROWN GROUPS, WITH INSIGHTS FROM BIOGEOGRAPHY
Kyle Richard Womack, M.S. Geo. Sci.
University of Texas at Austin, August 2011
Supervisor: James Sprinkle
96 pages, 66 references
Crinoids are the most primitive living members of the Phylum Echinodermata. Though still present in reduced numbers today, crinoids were the dominant echinoderms from the Ordovician to the Permian. The crinoid body plan consists of three major regions, the column, the calyx, and the arms. Each region serves important functions in crinoids. The column raises the rest of the body into the water column for more efficient feeding. The calyx contains the visceral mass and mouth. Arms extend out from the top of the calyx to trap microorgansisms and suspended organic particles in the water column. A re-evaluation of these functional units is undertaken to understand the importance of various structures and to obtain discrete characters for use in a cladistic analysis.
The relationship of crinoid crown groups has been an active area of research for the past couple of decades. With each proposed phylogenetic relationship, a new interpretation of thecal plate homology has been proposed. Here each study is re-examined in the light of new data. A review of functional morphology indicates a dual-reference system to be the most supported interpretation of plate homology. The two reference points in this system are the stem-cup and the cup-arm junctions, at the top and bottom of the calyx. The difference between a two-circlet and three-circlet crinoid is the presence or absence of the middle (basal) circlet. A new cladistic analysis is presented, with the topology of trees obtained giving support for the retention of Paleozoic crinoid stem and crown groups.
Crinoids appear abruptly in the fossil record. Questions pertaining to origins and ancestral stock abound. A biogeography study is employed to look at the distribution of crinoids from the Early to Middle Ordovician. Locality information, combined with an understanding of the movement of major plates, paleoclimate data, an understanding of larval distribution, and a review of similar studies carried out on different taxa, gives insight into possible radiation and dispersal patterns of crinoids from the first half of the Ordovician.
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INTERNALIZING THE CARBON EXTERNALITY: GREENHOUSE GAS MITIGATION'S FINANCIAL IMPACT ON ELECTRIC UTILITIES AND THEIR CUSTOMERS
James Terence Woodward, MPAff, MA
University of Texas at Austin, May 2010
Supervisor: Charles G. Groat
102 pages, 73 references, 13 tables
Social, political, and economic trends suggest that the United States may soon join other United Nations Framework Convention on Climate Change (UNFCCC) countries in drafting substantive, national climate change policy. After providing a brief overview of past and present climate action taken both nationally and internationally, this paper explores different economic solutions to address (he externalities of fossil fuel emissions. Alternatives include command-and-control regulation, a carbon tax, and a cap-and-trade program. Several factors, including domestic political anti-tax sentiment, suggest that a cap-and-trade framework is the most promising market-based alternative to reduce carbon emissions within the United States's electricity sector. Case studies focus on the power generation components of four Texas utilities: Austin Energy, CPS Energy of San Antonio, NRG Energy, and Luminant and assess cap-and-trade's ramifications on electricity prices. Utilities would seek to pass through to customers in the form of higher electricity prices up to 100 percent of expenses incurred from mitigating greenhouse gas (GHG) emissions. Three primary factors will determine how a given carbon dioxide cap-and-trade allowance price will affect the electricity price charged by utilities: the carbon intensity of the generation fuel mix, whether the wholesale electricity market is regulated or competitive, and whether greenhouse gas allowances are auctioned or grandfathered to covered entities. Consumer elasticity would determine resulting demand for the higher priced energy. Relatively inelastic electricity consumption could cause electricity sector customers to incur financial losses approximately eight times larger than producers by the year 2020 under a mature cap-and-trade framework. Furthermore, evidence suggests market-based GHG reduction tools such as a cap-and-trade schema alone are not sufficient to decarbonize the electricity generation sector. Without complementary regulatory policies that mandate transition to clean energy sources, cap-and-trade will only succeed in redistributing the opportunity cost associated with the carbon externality.
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NEW GEOPHYSICAL PARAMETERS FOR UNDERSTANDING THE EVOLUTION OF THE ST. ELIAS OROGEN, SOUTHERN ALASKA
Lindsay Lowe Worthington, Ph.D.
University of Texas at Austin, December 2010
Supervisor: Sean P.S. Gulick
241 pages, 125 references, 7 tables
The St. Elias Orogen is the result of oblique collision and flat-slab subduction in the Gulf of Alaska between North America (NA) and the Yakutat microplate (YAK). Extensive glaciation and a complex tectonic environment make this region a unique case study in which to examine the details of terrane accretion and the possible coupled influence of climate and tectonic drivers on the structural and topographic evolution of an orogenic wedge. The dataset for this project includes: 3 multi-channel seismic reflection surveys (~4000 km total seismic reflection data) and a ~450 km-long wide-angle seismic refraction profile.
Reflection seismic profiles across the offshore YAK-NA deformation front, provide constraints for quantifying Pleistocene deformation recorded in the glaciomarine Yakataga formation. Growth strata and kinematic fold analysis allow comparison of relative timing of fault activity, which reveals temporal and spatial shifting of deformation within the margin towards the onshore eastern corner of the orogen. This information is important not only for the development of regional tectonic models, but also for understanding how climatic shifts may have affected the evolution of margin architecture during Pleistocene glacial-interglacial periods.
Joint tomographic inversion of coincident reflection and refraction profiles constrains YAK crustal velocity and thickness. The offshore YAK crust ranges in thickness from 15 to 35 km, considerably thicker than normal oceanic crust. The crustal thickness and velocity structure support an oceanic plateau origin for the YAK microplate. Crustal velocity and structure are continuous across the YAK shelf except for a regional dip of the top of YAK crust of ~3 to the west. Moho arrivals across the profile do not mimic the dipping trajectory of the basement, indicating that the offshore YAK crust is doorstop-shaped, thinning in the convergence direction. This geometry leads to the following implications for the YAK-NA collision: first, uplift and deformation have intensified through time as successively thicker, more buoyant YAK crust attempts to subduct; second, current topography, exhumation and deformation patterns are partially controlled by underlying crustal geometry of converging YAK crust.
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A SUPERCONDUCTING GRAVIMETER FOR EVALUATION OF GROUNDWATER CHANGES IN THE FIELD
Hongqiu Wu, MSGeoSci
University of Texas at Austin, August 2011
Supervisor: Clark R. Wilson
81 pages, 35 references, 3 tables
The Superconducting Gravimeter (SG) is an extremely sensitive instrument that measures relative changes in gravity. It is based on the movement of a superconducting sphere levitated in a magnetic field created by current in superconducting coils. It is capable of detecting gravity variations as small as 10-11 ms-2. Because early production SG's lost helium at a steady rate, a large capacity dewar was required for reasonable periods of uninterrupted operation. In the late 1990's, Sumitomo Heavy Industries (SHI) developed a compact refrigeration system able to achieve liquid helium temperatures near 4K. It eliminates helium loss and allows a much smaller dewar to provide long intervals of continuous operation. These technical advances led us to develop an SG configured as a transportable field instrument. The goals were: 1) to package the entire SG system in two containers; 2) to test transport feasibility while the sensor remained in a superconducting levitated state; 3) to verify operability in field conditions; and 4) to determine the value of a transportable SG in groundwater and aquifer studies. We integrated the SG with a full weather station (measuring barometric pressure, rainfall, soil moisture etc.) and a geodetic GPS receiver (measuring vertical movement and atmospheric water vapor). All components were contained within enclosures constructed from angle and sheet aluminum. Each has dimensions ~1.5 x 0.8 x 1 m, total mass ~250 kg (including equipment) and can be transported easily by a medium truck while the sensor remained in a superconducting levitated state.
Temporal gravity variations measured by the SG include solid Earth tides, pole-tide, atmospheric pressure effect, ocean loading effect, and terrestrial water storage variations. Most of these can be well modeled, except the last term. We developed a standard procedure for SG data processing. The first field deployment of the SG system was for the study of the Edwards aquifer, a Karst aquifer system that provides water resources in Central Texas, and was operated by a monitoring well equipped with transducer to measure water level changes. The residual gravity changes measured by the SG were only sensitive to the water storage changes underground. With well level measurements, it can be used to estimate aquifer's specific yield.
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THE U.S. SMALL HYDROPOWER INDUSTRY: OPPORTUNITIES FOR DEVELOPMENT AND BARRIERS TO SUCCESS
David Tyler Wymond, M.A.
University of Texas at Austin, May 2011
Supervisors: J. Eric Bickel and David B. Spence
79 pages, 29 references, 13 tables
With many states recently enacting either renewable energy mandates or goals, the small hydropower industry has a unique opportunity to supply a growing portion of U.S. electricity supply. But the procedure to obtain a license for project development is unwieldy, increasingly wrought with regulatory hurdles at both the state and Federal levels. Government incentives exist that promote the development of small hydropower, but are insufficient to overcome the regulatory barriers faced by the industry. Although it is possible for small hydropower to supply a growing share of energy production in the U.S., it is unlikely that the full potential will be realized without substantial changes to the renewable energy regulatory system.
This study describes the current state of the regulatory system governing the development of small hydropower facilities in the United States. A basic overview of hydroelectric technology is discussed, followed by a detailed description of the process through which a project developer must apply for a Federal license to construct and operate a hydropower project. The current state of the U.S. small hydropower industry is examined, considering the potential opportunity for the industry to supply a growing share of the U.S. electricity supply. This analysis is supplemented by a discussion of the costs of project construction and an investigation into the regulatory barriers to project development.
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SENSITIVITY OF SEISMIC REFLECTIONS TO VARIATIONS IN ANISOTROPY IN THE BAKKEN FORMATION, WILLISTON BASIN, NORTH DAKOTA
Fang Ye, M.S.Geo.Sci.
University of Texas at Austin, May 2010
Supervisor: Robert H. Tatham
109 pages, 71 references, 29 tables
The Upper Devonian–Lower Mississippian Bakken Formation in the Williston Basin is estimated to have significant amount of technically recoverable oil and gas. The objective of this study is to identify differences in the character of the seismic response to Bakken interval between locations with high and poor production rates. The predicted seismic responses of the Bakken Formation will hopefully help achieve such discrimination from surface seismic recordings.
In this study, borehole data of Bakken wells from both the Cottonwood and the Sanish Field were analyzed, including density information and seismic P and S wave velocities from Sonic Scanner logs. The Bakken Formation is deeper and thicker (and somewhat more productive) in the Sanish Field and is shallower and thinner in the Cottonwood Field. The Upper and Lower Bakken shale units are similar and can be characterized by low density, low P and S wave velocities and low Vp/Vs ratios. The Sonic Scanner data suggest that the Upper and Lower Bakken shales can be treated as VTI media while the Middle Bakken may be considered as seismically isotropic.
Models of seismic response for both fields were constructed, including isotropic models and models with variations in VTI, HTI, and the combination of VTI and HTI in the Bakken intervals. Full offset elastic synthetic seismograms with a vertical point source were generated to simulate the seismic responses of the various models of Bakken Formation. This sensitivity study shows pronounced differences in the seismic reflection response between isotropic and anisotropic models. P-P, P-SV and SV-SV respond differently to anisotropy. VTI anisotropy and HTI anisotropy of the Bakken have different character. In particular, types of seismic data (P-P, P-SV, and SV-SV) and the range of source-receiver offsets that are most sensitive to variations in anisotropic parameters and fluid saturation were identified. Results suggest that bed thickness, anisotropy of the Upper and Lower Bakken shales, fractures/cracks and fluid fill in the fracture/cracks all influence the seismic responses of the Bakken Formation. The paucity of data available for “poorly” producing wells limited the evaluation of the direct seismic response to productivity, but sensitivity to potentially useful parameters was established.
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INVESTIGATION OF METHODS FOR PHOSPHATE DETERMINATION IN HIGH-ARSENATE SOLUTION : EL TATIO GEYSER FIELD, CHILE
Syed Daniel Zafar, BS
University of Texas at Austin, December 2011
Supervisor: Philip C. Bennett
25 pages, 28 references, 2 tables
In the present study, a spectrophotometric peak-ratio method and two reduction schemes were evaluated for the purpose of measuring trace H3PO4 in high-H3AsO4 solution (>400 μmol H3AsO4). This is extremely difficult due to the chemical similarity between H3PO4 and H3AsO4. At the El Tatio Geyser Field (ETGF), Chile, where P is very low, and As:P ratios are very high, it is almost impossible to measure H3PO4. H3PO4 is an important nutrient for microbial populations, and to characterize microbial ecology and the toxicity of arsenic the concentration of H3PO4 needs to be determined. This study evaluated the utility of an optimized molybdenum blue colorimetric method for analysis. Absorbance was analyzed at two different absorbance peaks in an effort to develop a method of H3PO4 quantification without pretreatment of samples. In addition, as HAsO2 does not interfere with H3PO4 measurement, two reducing agents were evaluated for reduction of H3AsO4 to HAsO2. The two reducing agents, NH3OH-HCl and Na2S2O4, were employed.
The scheme involving peak absorbance analysis was not effective with ETGF concentrations due to extensive overlap between peaks. The two reducing agents were also not found to be compatible with the molybdenum blue colorimetric method when employed with very high As concentration. NH3OH-HCl interfered with the molybdenum blue method and elevated absorbance of samples. Na2S2O4 reduced H3AsO4 completely with 20 µmol 1-1 H3AsO4 and 16 mmol 1-1 Na2S2O4. At 200 μmol 1-1 H3AsO4 and 160 mmol 1-1 Na2S2O4, however, S precipitated in solution and interfered with colorimetric analysis. None of the reduction reagents used were found to be suitable for effective reduction of H3AsO4 to determine trace ortho-P.
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