Browsing by Subject "Geochemistry"
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Item An Assessment of the Natural and Anthropogenic Geochemistry of the Red Mountain Creek Watershed: Ironton Mining District, Colorado(2014-04-29) Litt, JoshuaRed Mountain Creek is located in the rich mineralized San Juan Mountains of Southwestern Colorado, where mining from the mid 1800s through the late 1970s occurred. Sampling of the Uncompahgre River in the late 1970s, which is downstream of the five tailings ponds, showed high levels of heavy metals. It was assumed the remaining mine tailings were responsible for the high concentrations of heavy metals in the waters down-valley from the deposits. Thus, in 1983, remediation began with the use of direct re-vegetation of the deposits. This remediation was required as a result of National laws, which mandated the state of Colorado and the Idarado Mining Company develop a Remedial Action Plan (RAP). Interestingly, the tailings were assumed to be the sole source. Studies over the past twenty years, have suggested for site-specific locations, the highly mineralized zones may be additional sources of inputting heavy metals into streams. We assumed that heavy metal concentrations found in the streams come from the weathering of highly complex mineral assemblages, as well as from mining activities. It was our objective to establish the geochemistry in streams in the areas above and below mining activity and remediated areas and to evaluate the impact of remediation. Water quality data were collected for Aluminum (Al), Cadmium (Cd), Copper (Cu), Iron (Fe), Lead (Pb), Magnesium (Mg), Manganese (Mn), Zinc (Zn), and temperature, specific conductance, pH and dissolved oxygen. Twenty-seven samples were filtered with a 0.45?m membrane filter and twenty-seven were left unfiltered. Samples were collected in-stream after determining discharge for each stream. The samples of RMC were evaluated by using a Shapiro-Wilks test. There is a definitive difference between pH and dissolved metal concentrations when comparing streams on the east side to west side. In addition, there were five distinct confluences with Red Mountain Creek that provided significant changes in water quality. This was due to hydrothermally altered bedrock, which had and had not been mined.Item Black mangrove (Avicennia sp.) colony expansion in the Gulf of Mexico with climate change : implications for wetland health and resistance to rising sea levels(2010-12) Comeaux, Rebecca Suzanne; Allison, Mead A. (Mead Ashton); Bianchi, Thomas S.; Mohrig, David; Wilson, Clark R.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.Item Chemolithofacies of the Upper Cretaceous Buda Formation and Austin Chalk Group, south-central Texas : a product of integration of lithologic and chemical data(2016-12) Hendrix, Christopher K.; Loucks, R. G.; Rowe, Harry; Kerans, Charles; Fisher, WilliamThe Upper Cretaceous Cenomanian Buda Formation and Coniacian-Campanian Austin Chalk Group of Texas and northern Mexico are calcareous mudrock (chalk) successions deposited on the drowned lower Cretaceous Comanche platform. Investigations covering depositional systems, lithofacies, and diagenesis have been completed over the years, but no up-to-date chemostratigraphic studies have been conducted on either the Buda or Austin Chalk units. This investigation has supplemented sedimentological analysis with high-resolution X-ray-fluorescence (XRF) geochemical data. Two methods were employed to define chemofacies from an XRF dataset to test whether geochemical data can enhance description of the lithofacies and add insight to the lithostratigraphic analysis. Buda and Austin units are composed of four lithofacies in the subsurface of south-central Texas: (1) calcisphere globigerinid wackestone, (2) calcisphere globigerinid mud-dominated packstone, (3) calcareous mudstone, and (4) argillaceous calcareous mudstone. Observations of elemental curves plotted versus depth identified the alternation of calcite-rich chemofacies with dolomite-, clay-, and pyrite-rich chemofacies. Multiple iterations of hierarchical cluster analysis applied to the XRF dataset revealed seven chemofacies: (1) Ca-enriched, (2) Mg-enriched, (3) Al-enriched, (4) S-enriched, (5) P-enriched, (6) Zn-enriched, and (7) Ni-enriched. Neither chemofacies method is capable of defining lithofacies, but each can be used to substantiate mineralogical variability at the sub-lithofacies scale. The XRF-curve-based chemofacies identified large-scale oscillations in mineralogical composition while the HCA chemofacies identified mineralogical variability at the resolution of XRF sampling. Chemolithofacies are defined as lithofacies that are additionally characterized by chemofacies data. Delineation of the chemolithofacies is achieved by applying geochemical (and in this case mineralogical) descriptors to the lithofacies units based on the geochemical data. Ca-enriched calcisphere globigerinid wackestones and packstones are the dominant chemolithofacies of the Buda Formation and Austin Chalk Group. Calcisphere globigerinid wackestones, calcisphere globigerinid mud-dominated packstones, calcareous mudstones, and argillaceous calcareous mudstones enriched in dolomite, clays, and pyrite make up the other chemolithofacies. Variability in the chemolithofacies is attributed to rock units of more mixed mineralogy as a result of intermittent, sustained periods of increased extrabasinal sediment delivery to the shelf.Item Constraints from mantle xenoliths on the geodynamic evolution of Earth’s upper mantle(2014-05) Byerly, Benjamin Lee; Lassiter, John C.; Gardner, James E; Grand, Stephen P; Rowe, Michael C; Zhao, DonggaoGeophysical studies identify a region of slow seismic velocity mantle beneath the central Rio Grande rift that potentially represents a region of hot asthenospheric mantle that has replaced destabilized lithosphere. We determine that the majority of mantle xenoliths from Elephant Butte on the central Rio Grande rift axis are, based on their geochemical affinity to depleted mantle, derived from asthenospheric mantle that has accreted to the base of the Proterozoic lithosphere. Using mantle heat flow models, we estimate the boundary between residual lithosphere and accreted asthenosphere to be at ~45km depth. The amount of lithosphere thinning that has occurred cannot be accounted for by rift-related extension and we therefore suggest that convective removal of a large portion of Proterozoic lithosphere has occurred. Convecting upper mantle-derived peridotites display extreme isotopic depletions that are not observed in mid-ocean ridge basalts (MORB). Previous studies suggest that these isotopically ultradepleted domains represent rare refractory mantle domains that do not participate in MORB petrogenesis. We demonstrate the isotopically ultradepleted domains are not only a ubiquitous feature of convecting upper mantle, but are also capable of melting if advected beneath mid-ocean ridges. To explain the lack of MORB with ultradepleted isotopes, we suggest that MORB compositions are biased towards fertile enriched source components. Estimates of upper mantle composition based on MORB therefore overestimate the fertility of the upper mantle. The Lu-Hf system is commonly used to estimate the timing of melt depletion events in the lithospheric mantle. This is typically done with pseudoisochrons from genetically related mantle xenoliths. Most studies, however, misinterpret Lu/Hf – Hf isotopes correlations by using Cpx Lu/Hf ratios when whole rock Lu/Hf ratios are appropriate due to equilibration above the Lu-Hf closure temperature. Hafnium isotopes do not typically correlate with indicators of melt depletion, which suggests that Hf isotopes do not record ancient melting events. This is likely due to overprinting of Hf isotopes by later metasomatic events.Item Crustal xenoliths from Potrillo Maar: implications for evolution of continental crust beneath the southern Rio Grande rift(Texas Tech University, 2003-08) Chattopadhyay, IndraniThe mid-crustal xenoliths from Potrillo maar record a petrologic and geochemical history that has until now been unknown from the Potrillo volcanic field. The igneous and meta-igneous xenoliths are samples of one or more plutonic bodies that crystallized at depths from 7-14 km (middle to upper crust). The rock unit ranges in composition from hornblende biotite diorite to quartz monzonite and monzogranite; it is broadly alkalicalcic The initial Sr87Sr86 suggests that the source region is heterogeneous or that the parental magmas were contaminated by crustal material. At least three geochemical groups can be identified, primarily on the basis of silica content. There is considerable overlap between groups 1 and 2, and the boundary between these two groups cannot be distinguished graphically. The third group is granitic and is geochemically distinct from groups 1 and 2. A dioritic composition is thought to represent mafic parental magma. Its calculated liquidus temperature at 2% H2O and 4 Mpa pressure is 1172°C. The presence of fossiliferous limestone xenoliths indicates that the Potrillo maar eruption sampled rocks of late Paleozoic age. However, the age of marble and quartzite xenoliths are not known. The quartzite xenoliths are relatively undeformed, but isoclinal folding in some of the marble xenoliths suggests subsurface deformation that has not been observed in local surface exposures of metasedimentary rocks. One model proposed for the crust under the southern Rio Grande rift assumes that the marble is late Paleozoic in age. The fossiliferous limestones are late Paleozoic in age and are older than the plutonic rocks. The relative age of the deformed marbles in this model is not clear, it can be deformed with the plutonic rocks or due to an earlier regional extensional event. In the second model, marble is proposed to result from contact metamorphism in the aureole of a plutonic rock body at a depth of 7-14 km. The presence of marble and calc-silicate xenoliths in dioritic blocks is consistent with a correlation of the marble with surface exposures of the Castner Marble in the Franklin MountainsItem Deposition and diagenesis of the Smackover Formation, south-central Alabama(Texas Tech University, 1977-12) Leiker, Loren MichaelNot availableItem Evidence from high-temporal-resolution strain rates for strain softening due to episodic fluid influx at Passo del Sole, Central Swiss Alps(2012-12) Stacy, Sarah Jean; Carlson, William, 1952-; Cloos, Mark; Ketcham, Richard ABerg (2007) determined hand-sample-scale high-temporal-resolution strain rates from rotated garnet for two samples of quartzose pelitic gneiss at Passo del Sole, Central Swiss Alps, documenting a correlation between dramatic increases in strain rate and compositionally anomalous garnet growth zones. Considering additional evidence that these anomalous zones resulted from externally derived ephemeral fluid flow, he concluded that increased strain rates at Passo del Sole are the result of strain softening caused by fluid influx. This study tests Berg's interpretation by calculating new hand-sample-scale high-temporal-resolution strain rates for two additional samples of the same gneiss: a control sample (Sample PDS 03-30) that shows no unusual zoning patterns, implying that it was unaffected by fluids; and another (Sample PDS 03-2) that features a prominent Ca spike, suggesting that it has been affected by fluid influx. Unique features of garnet from this locality--contemporaneity of chemical zones, near-simultaneous nucleation, size-proportional growth, and rock-wide chemical equilibrium--were exploited to calculate strain rates of unprecedentedly high temporal resolution. Thermodynamically modeled temperatures for several growth-zone boundaries in each garnet crystal were combined with a regional heating rate of 11.5 ± 3.5 °C/Myr (presumed constant) and measured deflections of inclusion trails in each zone to calculate strain rates for several discrete time increments during garnet growth. Sample PDS 03-2 displays a 2- to 16-fold increase in strain rate that correlates with growth of the high-Ca zone; strain rates are 0.4 x 10⁻¹⁴ s⁻¹ to 4.1 x 10⁻¹⁴ s⁻¹ for zones with normal Ca concentration and 9.1 x 10⁻¹⁴ s⁻¹ to 17.9 x 10⁻¹⁴ s⁻¹ for the high-Ca zone. Distinct amongst all analyzed samples from Passo del Sole, Sample PDS 03-30--which has not been affected by fluid influx--shows no fluctuations in strain rates, which remain low and similar (0.2 x 10⁻¹⁴ s⁻¹ to 2.6 x 10⁻¹⁴ s⁻¹) across all zones. Results from this study therefore further substantiate the correlation of high strain rates with compositionally anomalous zones, strengthening the interpretation that elevated strain rates at Passo del Sole result from strain softening caused by episodic, externally controlled flow of fluids through the system during synkinematic garnet growth.Item An experimental and simulation study of the effect of geochemical reactions on chemical flooding(2010-12) Chandrasekar, Vikram, 1984-; Delshad, Mojdeh; Pope, Gary A.The overall objective of this research was to gain an insight into the challenges encountered during chemical flooding under high hardness conditions. Different aspects of this problem were studied using a combination of laboratory experiments and simulation studies. Chemical Flooding is an important Enhanced Oil Recovery process. One of the major components of the operational expenses of any chemical flooding project, especially Alkali Surfactant Polymer (ASP) flooding is the cost of softening the injection brine to prevent the precipitation of the carbonates of the calcium and magnesium ions which are invariably present in the formation brine. Novel hardness tolerant alkalis like sodium metaborate have been shown to perform well with brines of high salinity and hardness, thereby eliminating the need to soften the injection brine. The first part of this research was aimed at designing an optimal chemical flooding formulation for a reservoir having hard formation brine. Sodium metaborate was used as the alkali in the formulation with the hard brine. Under the experimental conditions, sodium metaborate was found to be inadequate in preventing precipitation in the ASP slug. Factors affecting the ability of sodium metaborate to sequester divalent ions, including its potential limitations under the experimental conditions were studied. The second part of this research studied the factors affecting the ability of novel alkali and chelating agents like sodium metaborate and tetrasodium EDTA to sequester divalent ions. Recent studies have shown that both these chemicals showed good performance in sequestering divalent ions under high hardness conditions. A study of the geochemical species in solution under different conditions was done using the computer program PHREEQC. Sensitivity studies about the effect of the presence of different solution species on the performance of these alkalis were done. The third part of this research focused on field scale mechanistic simulation studies of geochemical scaling during ASP flooding. This is one of the major challenges faced by the oil and gas industry and has been found to occur when sodium carbonate is used as the alkali and the formation brine present in situ has a sufficiently high hardness content. The multicomponent and multiphase compositional chemical flooding simulator, UTCHEM was used to determine the quantity and composition of the scales formed in the reservoir as well as the injection and production wells. Reactions occurring between the injected fluids, in situ fluids and the reservoir rocks were taken into consideration for this study. Sensitivity studies of the effect of key reservoir and process parameters like the physical dispersion and the alkali concentration on the extent of scaling were also done as a part of this study.Item An experimental calibration of chlorine isotope fractionation between amphibole and fluid at 700 °C and 0.2 GPa(2013-08) Cisneros, Miguel; Barnes, Jaime DanielleA Cl stable isotope fractionation factor between amphibole and fluid has been determined at 700 °C and 0.2 GPa. Rates of isotope exchange between pargasite and water at 600-800 °C were slow; therefore synthesis of amphibole in the presence of a fluid was necessary to facilitate the incorporation of Cl into amphibole. Hastingsite was synthesized from an oxide mixture and reacted with a NaCl-bearing supercritical fluid for periods of 3 to 14 days, approximately at the wüstite-magnetite buffer. Based on these synthesis-reaction experiments, the fractionation between hastingsite and a NaCl-bearing solution (~20000 ppm Cl) at 700 °C is 103lnαamphibole-fluid = 0.19‰ ± 0.23‰. These data display near zero fractionation at 700 °C, but suggest that amphibole is slightly enriched in 37Cl relative to the fluid, in agreement with empirical and theoretical results.Item Geochemical and geochronological relationships between granitoid plutons of the Biga Peninsula, NW Turkey(2012-05) Black, Karen Naomi; Catlos, Elizabeth Jacqueline; Barnes, Jaime D.; Eichhubl, PeterThe Aegean Sea is considered to be a classic back-arc basin. Back-arc basins may develop by active processes including retreat of the overriding plate or upwelling from the subducting slab. Alternatively, back-arc basins may develop as passive responses to regional tensional stresses. The Biga Peninsula of western Turkey provides an opportunity to explore and test these models. The Biga region is characterized by granitoid plutons of Cretaceous to Miocene age that may provide insight into the nature of extension. This study focuses on understanding the evolution of three of these plutons, the Kozak, Eybek, and Kestanbolu. Geochemical and geochronological data and cathodoluminescence (CL) images of the rocks and zircons were acquired. The first in situ (in thin section) ion microprobe U-Pb ages of zircon, and the first zircon ages ever reported from the Kozak and Eybek plutons are presented. Zircon ages range from 36.5±6.6 Ma to 17.1±0.7 Ma (238U/206Pb, ±1) with two ages from a single grain of 280±18 Ma and 259±14 Ma. Samples from the Kozak and Eybek plutons are magnesian, calc-alkalic, and metaluminous, whereas the Kestanbolu rocks are magnesian, alkali-calcic, and metaluminous with one ferroan sample. The Rb vs. (Y+Nb) diagram suggests the Kozak and Kestanbolu plutons have a volcanic arc source, whereas the Eybek pluton records a within plate setting. CL imagery documents magma mixing, brittle deformation, and fluid- rock interactions based upon cracked plagioclase cores, cross-cutting microcracks, and fluid reaction textures of myrmekite and red rims on alkali feldspar. The plutons were generated following the collision of the Sakarya continent with the Anatolide-Tauride block. Geochemical data suggest the Kozak and Kestanbolu granitoids were generated by fluid flux melting from dehydration of the subducting slab of the Anatolide-Tauride block. The Kestanbolu granitoid intruded into the Vardar Suture north of this collision, whereas the Eybek pluton was created within the lithosphere during exhumation of the Kazdağ Massif. The Eocene - Oligocene zircon ages indicate emplacement and initial crystallization of the plutons. Early Miocene ages indicate ongoing extension in the region at this time and are consistent with earlier interpretations that subduction slab roll-back along the Hellenic arc formed the extensional environment in the region at this time.Item Geochemical effects in two-phase flow(2005) Zuluaga, Elizabeth; Lake, Larry W.Commercial reservoir simulators usually neglect the effect of the permeable media on phase equilibrium, and the thermodynamic interaction between the aqueous phase and the other phases present in the reservoir. These assumptions are not satisfied when gas is injected or produced, because water will be vaporized from the reservoir. This dissertation derives analytical and semianalytical solutions to predict water vaporization and mineral precipitation for gas injection and production in hydrocarbon reservoirs. It also develops and incorporates into the models phase equilibrium relationships that include the effect of capillary pressure and salinity in the predictions. A new equilibrium constant for mineral precipitation has been derived that takes into account capillary pressure and interfacial forces. For gas injection, a traveling wave solution has been adopted with a correction proposed to honor the material balance. The traveling wave solutions were tested against results from the compositional simulator Generalized Equation of State Model (GEM) and against experimental data. The results from the traveling wave solution matched the experimental data closely while GEM failed to make good predictions. A semi-analytical model has been developed for gas production. This semi-analytical model was also tested against results from GEM. The results closely matched the GEM solutions in the absence of capillary pressure, interfacial forces and salinity effects. The results of this research show that the reservoir could be completely depleted from water near the wellbore when gas is produced or under-saturated gas is injected. Therefore, the existence of a residual water saturation value has to be re-evaluated in reservoir modeling. It is also shown that the wetting phase is mobile even at extremely low values of wetting phase saturation: the paradigm of an immobile residual phase is mostly imposed by the limitations of measuring devices in the laboratory and by the length of time of the experiments used to measure relative permeability. A new method to obtain relative permeability at very low wetting phase saturation has been derived, based on fitting the relative permeability exponent to vaporization data in the falling rate period. This research has also quantified the reductions in porosity and absolute permeability caused by mineral precipitation.Item Geochemistry and high-resolution chemostratigraphy of the Haynesville Formation, East Texas(2015-05) Bitar Nehme, Rita Abdo; Rowe, Harry; Fisher, W. L. (William Lawrence), 1932-; Kerans, CharlesThe Upper Jurassic Haynesville Formation of East Texas and Louisiana is an organic-rich calcareous mudrock that is Kimmeridgian in age. It underlies the less calcareous Bossier Shale, and it overlies the Smackover Formation limestone. The Haynesville has low permeability, but a relative high porosity, compared to other mudrock formations. Mudrocks are the most common sedimentary rock and some of the most challenging to study, analyze and understand. Despite having a homogeneous appearance on a macroscopic scale, mudrocks often have high variability in facies and composition on the microscopic scale and elemental level. Many studies and methods have been developed to identify facies and stratigraphic variations in mudrocks. A complete understanding of these variations is valuable to comprehend paleoenvironments, paleoclimate and paleoceanographic conditions. Mudrocks studies are also beneficial to shale exploration because these formations, which have a high hydrocarbon content, can be targeted by oil and gas companies for exploration and production. Geochemical methods, chemostratigraphy in particular, will be used in this thesis to complement core description, petrophysical studies and sedimentological studies. This thesis focuses on acquiring chemostratigraphic data from X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) measurements to identify elemental and mineralogical variations in the T. W. George core, from the Haynesville Formation in Harrison County, Texas. The data are linked to core description and are analyzed using Hierarchical Cluster Analysis (HCA) to acquire a better understanding of the paleoceanographic conditions and depositional environments that controlled the sediment deposition of the Haynesville Formation. The Haynesville Formation comprises a Ca-rich lower Haynesville, a more Ca-rich upper Haynesville, and underlies the Si-rich and Ca-poor Bossier. The dominant condition during deposition is anoxic/euxinic in the lower Haynesville becoming dysoxic in the upper Haynesville and more oxygenated in the Bossier Formation. The greenhouse climate of the Late Jurassic led to the deposition of strata yielding petroleum source rocks such as the Haynesville Formation that today have great economic value. Thus, studying the Haynesville has both academic and economic importance.Item Geologic setting and reservoir characterization of Barnett Formation in southeast Fort Worth Basin, central Texas(2014-08) Liu, Xufeng; Fisher, W. L. (William Lawrence), 1932-; Loucks, R. G.The Mississippian Barnett Formation is a prolific shale-gas reservoir that was deposited in the Fort Worth Basin, Texas. Many previous studies of the Barnett Formation have been conducted in the main production area; few studies have been made of the Barnett Formation in the southern part of the basin, which is a less productive area. In the present research, several cores from the Barnett Formation in Hamilton County, southeast Fort Worth Basin, are studied in detail. Two vertical, continuous cores from Hamilton County, Texas, were studied to delineate the depositional setting, lithofacies, pore types, and reservoir quality of the Barnett Formation in the area. Five lithofacies were defined by analysis of the two cores: (1) laminated clay-rich silty and skeletal peloidal siliceous mudstone; 2) laminated skeletal silty peloidal siliceous mudstone; 3) nonlaminated silty peloidal calcareous mudstone; 4) laminated and nonlaminated skeletal calcareous mudstone; and 5) skeletal phosphatic packstone to grainstone. As indicated from this study, the dominant organic matter type is a mixture of Type II (major) and Type III (minor) kerogen having a mean TOC content of approximately 4%. Analysis of Rock Eval data shows that most of the interval is within the oil window; calculated Ro is approximately 0.9%. Organic geochemistry shows that the hydrocarbon generation potential of the abundant oil-prone kerogen was excellent. Mineralogical analysis reveals that the two types of siliceous mudstone, which are similar in composition to the siliceous mudstone in the main producing area in the northern Fort Worth Basin, are good for hydraulic fracturing and production, but they are also limited by their marginal thickness. Organic matter pores, which are the dominant pore types in these two cores, are consistent with pore types found in currently producing wells in the Newark East Field. This research also suggests that the deposition of Barnett Formation was controlled largely by basinal geometry, suspension settling, and slope-originated gravity-flow events. Skeletal deposits and carbonate-silt starved ripples suggest gravity-flow deposits and bottom-current reworking during deposition. Redox-sensitive elements and degree of pyritization both indicate anoxic/euxinic conditions during the deposition of the Barnett Formation.Item Geomorphic and Geochemical Characteristics of Five Alpine Fens in the San Juan Mountains, Colorado(2012-11-26) McClenning, Bree Kathleen 1985-Fens are abundant in the San Juan Mountains. By exploring the geomorphology and geochemistry of fen wetlands, the functions that fens serve can be better understood. In this research, two main studies were conducted involving the geomorphology and geochemistry of fens. The first study involved a complex investigation of the geomorphology of five fen sites in the San Juan Mountains near Silverton, Colorado. Geomorphic maps were constructed for each fen site at a scale of ~1:3,000. A geomorphic classification scheme was then made based on fen location, and fens were placed in one of three categories: 1) valley-bottom, 2) valley-side, and 3) terrace. Fen circularity and elongation values were calculated for thirty fens to determine morphometry. A pattern for elongation of fens emerged between the three types of alpine fens with valley-bottom fens having an average elongation value of 1.7, valley-side 2.4, and terrace 1.9. Valley-side fens are more elongated than valley-bottom and terrace fens, which exhibit similar elongation values. In addition, sediment samples at each site were sectioned along visual breaks in the sediment column and were sieved. Mean phi values were calculated for each section and at each site. The mean phi values at California Gulch, Glacial Lake Ironton, Howardsville, Red Mountain Pass North, and Red Mountain Pass South, are 0.2112, 0.9045, 1.6028, 0.0178, and 1.0516, respectively. Overall, coarse-grained particles are associated with valley-side fens, and medium-grained particles are associated with valley-bottom and terrace fens. The second part of the study involved investigating the geochemistry of fen sediment. The geochemistry portion of this research focused on concentration and isotopic ratios of Pb and the amount of 137Cs in fen sediment to better understand variations of Pb with depth and calculate approximate sedimentation rates. Based on isotopic ratios of Pb, binary mixing was determined with the presence of ore mineralized Pb and non-ore mineralized. Binary mixing of two types of ore-mineralized Pb is present at the Howardsville fen and both ore-mineralized and non-ore mineralized Pb is present at the Red Mountain Pass North fen. Based on 137Cs in fen sediment at Howardsville, an average rate of deposition of sediment is approximately 0.16 cm/yr, with a visible change in sedimentation rates pre- and post-1960s.Item Ground-water geochemistry of the Ogallala Aquifer in the Southern High Plains of Texas and New Mexico(Texas Tech University, 1980-12) Potratz, Victoria YekoConcentrations of calcium, magnesium, potassium, sulfate, and chloride ions in the ground water generally increase from the north to the south in the Ogallala Aquifer of the Southern High Plains of West Texas and eastern New Mexico. In the south, higher concentrations of solutes generally occur in areas which are underlain by Cretaceous rocks and are located beneath large saline lakes. The distribution of bicarbonate and flouride ions and also silica molecules are variable throughout the aquifer. High concentrations of nitrate ions usually occur south of the northern edge of the Cretaceous boundary and along the northeastern edge of the aquifer. The primary sources of solutes in the ground water north of the Cretaceous subcrop are the weathering and dissolution of potassium feldspar, biotite, plagioclase feldspar, calcite, and dolomite. Minor amounts of sodium, sulfate, and chloride may have been added to the ground water by seepage of oil and gas field brines into the aquifer. It is proposed that ground water south of the Cretaceous subcrop obtains additional sodium, sulfate, and chloride ions from the mixing of saline Cretaceous water with the Ogallala water. The mixing between the two aquifers may result from a difference in head between the two aquifers or by diffusion. In these areas of mixing, the sodium ions from the Cretaceous water may be exchanging for calcium and magnesium ions on clay minerals in the Ogallala Formation. Some of the calcium ions produced from the exchange are probably combining with bicarbonate ions and precipitating calcium carbonate. Amorphous silica and flourite may be precipitating in several areas of the aquifer along with calcite and is probably limiting the concentrations of silica, flourine, calcium, and to a minor degree bicarbonate.Item Investigation of CO₂ seeps at the crystal geyser site using numerical modeling with geochemistry(2012-05) Kim, Eric Youngwoong; Srinivasan, Sanjay; EICHHUBL, PETERCarbon Dioxide (CO₂) sequestration requires that the injected CO₂ be permanently trapped in the subsurface and not leak from the target location. To accomplish this, it is important to understand the main mechanisms associated with CO₂ flow and transport in the subsurface once CO₂ is injected. In this work CO₂ seeps at the Crystal Geyser site were studied using modeling and simulation to determine how CO₂ geochemically reacts with formation brines and how these interactions impact the migration of CO₂. Furthermore different scenarios for CO₂ migration and seepage along the Grand Wash fault are studied and the possible outcomes for these different scenarios are documented. The GEM (Generalized Equation-of-State Model) from CMG Ltd. was used to perform the simulation studies. A 2-D model was built without geochemical reactions to mainly study the mechanism associated with dissolution of CO₂ gas. The process of CO₂ release from the brine as the fluid mixture flows up along the fault was modeled. Then, 3-D models with geochemical reactions were built for CO₂ migration corresponding to two different sources of CO₂ - deep crustal ₂ and CO₂-dissolved in groundwater. In both these cases, CO₂ reacted with the aqueous components and minerals of the formation and caused carbonate mineralization. In the case of deep crustal CO₂ source, there were vertical patterns of calcite mineralization simulated along the fault that indicated that calcite mineralization might be localized to isolated vertical flow paths due to vertical channeling of CO₂ from the crust. In the case of CO₂-dissolved groundwater flowing along the sandstone layers, calcite mineralization is spread over the entire fault surface. In this case, the groundwater flow is interrupted by the fault and there is vertical flow along the fault until a permeable sandstone layer is encountered on the other side of the fault. This vertical migration of CO₂-saturated brine causes a release in pressure and subsequent ex-solution of CO₂. As a result, modeling allowed us to establish difference in surface expression of CO₂ leakage due to two different CO₂ migrations scenarios along the fault and helped develop a scheme for selecting appropriate model for CO₂ leakage based on surface observation of travertine mounds. A key observation at the Crystal Geyser site is the lateral migration of CO₂ seep sites over time. These migrations have been confirmed by isotope studies. In this modeling study, the mechanism for migration of seep sites was studied. A model for permeability reduction due to precipitation of calcite was developed. It is shown using percolation calculations that flow re-routing due to permeability alterations can result in lateral migration of CO₂ seeps at rates comparable to those established by isotope dating.Item Issues of engineering and geochemistry in the sequestration of carbon dioxide in geological formations-saline aquifers(Texas Tech University, 2004-05) Garcia-Orrego, Gloria StellaDynamic tests were conducted to evaluate the feasibility of sequestering carbon dioxide (CO2) in a carbonate dolomite reservoir. Two injection rates, 5.696E-06 cubic feet/ min (0.1613 cc/min (20 pore volumes)) and 3.467E-05 cubic feet/min (0.982 cc/min (120 pore volumes)) were tested to observe changes in petrophysical parameters, particularly permeability and porosity at each rate. The low injection rate allowed the evaluation of the effect on the bulk of the reservoir. And the high injection rate to evaluate the effect of dissolution on the face of the formation. The tests were carried out at reservoir simulated conditions (2000 psia (140.64 atm) and 150°F (65.5°C)). San Andres dolomite formation cores from wells 744 and 745 drilled in the Levelland Field were used for this study. The dolomite formation is cemented by calcite and it has a high content of anhydrite. The formation brine of the Permian Basin was used to inject the cores. This brine has sodium 18,000 mg/L, chlorine 46,200 mg/L, calcium 6000 mg/L, sulfate 4880 mg/L, magnesium 1820 mg/L and potassium 1510 mg/L. The injection of low pore volumes was found to reduce the permeability by about 50%, and the pore volume and porosity by about 25%. The total equilibrium magnetization (Mo) from NMR T2 distribution is decreased by about 17%, indicating substantial reduction in porosity and permeability. The small pore sizes (bulk volume irreducible-BVI) increased on average by about 70% and the large pore sized (free fluid index-FFl) decreased by about 24%. The injection of high pore volume CO2 showed a slight increase in the petrophysical properties, permeability and porosity. The total equilibrium magnetization, B VI, and FFI did not present remarkable change. At the onset of this research, it was still uncertain how the interaction between CO2 and formation brine affects the geochemistry of the reservoir. Therefore, several static tests under supercritical conditions (1070 psia (78 atm) and 88°F (31.TC)) and under reservoir conditions with and without rock samples were carried out. After running the static tests for seven days, a precipitate formed from the brine after reaction with CO2 was obtained. The precipitate was analyzed using scanning transmission electron microscopy (STEM) to identify the specimen structure and to obtain a chemical analysis using an energy-dispersive spectrometry (EDS). Also, X-ray diffraction method (XRD) was used to identify the new minerals formed as a consequence of the interaction between CO2 and formation brine. Observations indicate that the precipitated is formed primarily by calcite, gypsum, halite and other mineral salts. On the basis of the previous observations, it can be concluded that at low pore volumes, a compact dissolution of anhydrite took place, followed by deposition of material dissolved from the rock and/or precipitation of the salt dissolved from brine. Consequently, the permeability and porosity were significantly reduced. In contrast, these effects in high pore volumes injected were masked by high dissolution of the anhydrite, leading to the formation of new flow paths (similar to wormholing in acidizing operation), and an increase in permeability and porosity. However, the increase in petrophysical properties could be offset by a reduction caused by precipitation of material, either from the dissolved salts in the brine or from the dissolved rock. Another objective of this investigation was to determine the amount of shale in a sandstone reservoir. This is an important issue for evaluating the storage capacity of given aquifer/ reservoir as a candidate for CO2 sequestration. A non-linear relationship of gamma ray index to volume of shale has been derived in a self-consistent formulation of emission and attenuation of gamma rays within the shale-sand composite. The technique to produce the derivation includes the self-shielding attenuation effects that occur at higher volumes of the shale gamma ray emitters. The effects of porosity and grain density of the constituents are included in the relationship of shale volume to gamma ray index. The new approach is applied to log data from the San Jorge Basin in Argentina.Item Mineralogy and geochemistry of the non-sulfide Zn deposits in the Sierra Mojada district, Coahuila, Mexico(2010-08) Ahn, Hye In; Kyle, J. Richard; Bennett, Philip C.; Gilg, H. AlbertThe 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. [delta]¹⁸O[subscriptVSMOW] = 21.9 ± 0.5[per mille]), whereas [delta]¹³C[subscriptVPDB] values range from -8.4 to -1.1 [per mille]. 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 [per mille]. Formational temperature of smithsonite is calculated to be between 26 ~ 40 °C 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.Item Natural fracture cementation in the Marcellus Formation(2013-05) Pommer, Laura Elizabeth; Gale, Julia F. W.; Eichhubl, PeterIn order to test the hypothesis that fractures in outcrops are equivalent to subsurface fracture systems I compare fracture cement morphology, texture, mineralogy and geochemistry from a suite of outcrop samples from Union Springs, NY, with fractures in four cores from a currently producing reservoir in southwest Pennsylvania. Transmitted light-microscope petrography and cold cathodoluminescence of calcite of outcrop and core samples reveals a variety of cement morphologies including crack-seal and blocky fracture cement textures that are interpreted as a record multiple repeated stages of fracture opening and sealing, as well as fibrous calcite fill and other mineral phases. The stable isotopic composition of calcite fracture cements from different fracture types in cores and outcrop range from -21.5 to +4.4‰ δ13C PDB and -8.0 to -12.0 ‰ δ18O PDB and indicate calcite precipitation temperatures between 46 and 89°C. Fluid inclusion microthermometry from secondary fluid inclusions indicates trapping temperatures between 110 and 120°C. Microprobe analysis of fracture calcite cement indicates a range in Fe, Mn, and Mg composition, with subsurface and outcrop cement of similar composition. Assuming burial history predicts thermal history, isotopic compositions together with fluid inclusions suggest calcite precipitated in vertical fractures during prograde burial, during the Acadian to early Alleghanian orogenies. These findings indicate that fractures in outcrops of the Marcellus Formation can be used as a proxy for those in the subsurface.Item New insights into the carbon isotope composition of speleothem calcite : an assessment from surface to subsurface(2012-05) Meyer, Kyle William; Banner, Jay L.; Breecker, Dan O.; Musgrove, MaryLynnThe purpose of this study was to provide new insights into the interpretation of speleothem (cave calcite deposit) δ13C values. We studied two caves in central Texas, which have been actively monitored for over 12 years. We compared δ13C values of soil CO2 (δ13Cs), cave drip water (δ13CDIC), and modern cave calcite (δ13Ccc). Measured average δ13C values of soil CO2 were -13.9 ± 1.4‰ under mixed, shallowly-rooted C3-C4 grasses and were -18.3 ± 0.7‰ under deeply-rooted ashe juniper trees (C3). The δ13CDIC value of minimally-degassed drip water in Natural Bridge Caverns was -10.7 ± 0.3‰. The carbon isotope composition of CO2 in equilibrium with this measured drip water is -18.1 ± 0.3‰. The agreement between juniper soil CO2 and drip water (within ~0.2‰) suggests that the δ13C value of drip water (δ13CDIC) that initially enters the cave is controlled by deeply-rooted plants and may be minimally influenced by host-rock dissolution and/or prior calcite precipitation (PCP). At Inner Space Caverns, δ13CDIC values varied with vegetation above the drip site, distance from the cave entrance, and distance along in-cave flow paths. Whereas CO2 derived from deeply-rooted plants defines the baseline for drip water δ13CDIC entering the caves, kinetic effects associated with the degassing of CO2 and simultaneous precipitation of calcite account for seasonal variability in δ13CDIC and δ13Ccc. We documented increases in δ13CDIC at a rate of up to 0.47‰/hour during the season of peak degassing (winter), suggesting that δ13CDIC variations may be controlled by total elapsed time of CO2 degassing from drip water (Ttotal). We also observed seasonal shifts in the δ13C values of modern calcite grown on glass substrates that are correlated with shifts in drip water δ13CDIC values and drip-rate. Therefore, we suggest that increased aridity at the surface above a given cave results in, slower drip-rates, higher Ttotal, and therefore higher δ13CDIC values. We propose that large variability (>2‰) in speleothem δ13Ccc values dominantly reflect major vegetation changes, and/or increasing Ttotal by slowing drip-rates. Based on these findings, variability in speleothem carbon isotope records may serve as a proxy for paleoaridity and/or paleovegetation change.