Browsing by Subject "Trace elements"
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Item Depositional and diagenetic processes in the formation of the Eocene Jackson Group bentonites, Gonzales County, Texas(2011-12) Michaelides, Michael Nicholas; Kyle, J. Richard; Gardner, James; Heister, Lara; Serenko, ThomasBentonite 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. vii 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.Item Habitat use and trophic structure of Atlantic tarpon (Megalops atlanticus) inferred from geochemical proxies in scales(2016-05) Seeley, Matthew Edward; Black, Bryan A.; Walther, Benjamin D.; Fuiman, Lee AAtlantic tarpon, Megalops atlanticus, are highly migratory euryhaline predators that occupy different habitats throughout life. Atlantic tarpon are known to inhabit oligohaline waters, although the frequency and duration of movements across estuarine gradients into these waters are poorly known. This species supports over a two billion dollar industry within the Gulf of Mexico and is currently listed as vulnerable by the International Union for the Conservation of Nature (IUCN). Analysis of trace element and stable isotope compositions of growth increments in fish scales is a non-lethal method for reconstructing migrations across estuaries in vulnerable species. We analyzed Atlantic tarpon scales from the Texas coast to validate this method using inductively coupled plasma mass spectrometry (ICP-MS) for trace elements and isotope ratio mass spectrometry (IR-MS) for stable isotope ratios. Multiple scales and otoliths were taken from the same individual to confirm the consistency of elemental and isotopic uptake within the same individual and between structures. Results show that scale Sr/Ca and δ13C are effective proxies for salinity, while increases in δ15N are consistent with known trophic shifts throughout life history. Patterns of elemental concentrations and isotope values across scales within an individual were consistent with each other. Scale and otolith transects contained the same overarching trend with comparable shifts in elemental concentrations across growth increments in the two structures. Migratory contingents, or groups within distinct populations that exhibit different patterns of habitat use and movement across salinity gradients, were identified. The distribution of contingents indicated that migratory behavior is highly variable, with some, but not all fish transiting estuarine gradients into oligohaline waters. Yet, the majority of individuals sampled exhibited early life residency in oligohaline waters. This work demonstrates the use of low salinity habitats by Atlantic tarpon. Our validation of the methods for analyzing scales will provide novel opportunities to monitor fish migrations across salinity gradients.Item The modern assessment of climate, calcite growth, and the geochemistry of cave drip waters as a precursor to paleoclimate study(2011-08) Casteel, Richard Cain; Banner, Jay L.; Sharp, Jr., John M.; Quinn, Terrence M.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.Item Physical and geochemical response in cave drip waters to recent drought, central Texas, USA : implications for drought reconstruction using speleothems(2015-08) Hulewicz, Michelle; Banner, Jay L.; Breecker, Dan; Musgrove, MaryLynnA five-year study (2009-2014) of eight drip sites in Inner Space Cavern (IS), a cave on the Edwards Plateau in central Texas, was undertaken to assess the physical and geochemical response of cave drip waters to extreme drought. Drip rate, calcite growth rate, and dripwater geochemistry were monitored before, during, and after the peak of a record-breaking drought in central Texas that began and peaked in 2011, and which continued through to early 2015. Three groups of drip sites are identified based on average drip rate (slow sites, 0.2 -- 0.4 mL/min; intermediate sites, 1.2 -- 4.4 mL/min; fast sites, 6.7 -- 18 mL/min) and similarities in geochemical variation. Drip rates of slow sites have the lowest rate and magnitude of response to changes in hydrological conditions, while fast sites have the largest rate and magnitude of response. In contrast, the geochemical response to drought of the three groups does not correspond to the drip rate response. Slow and fast sites exhibit limited geochemical responses to changes in hydrologic conditions, including dripwater Mg/Ca, Sr/Ca, and Ba/Ca ratios, Sr isotope values, Ca concentrations, and oxygen isotope values. This lack of response indicates limited water-rock interaction (WRI) and/or prior calcite precipitation (PCP) affects these dripwaters. Intermediate drip sites exhibit the greatest geochemical response to changes in hydrologic conditions, including extreme drought, expressed by a decrease in Sr isotope values and an increase in Mg/Ca ratios during drier periods. Quantitative modeling indicates that both WRI and PCP can account for trace-element and Sr isotope variations at intermediate sites. The peak of the drought in 2011 coincides with high cave-air CO₂ and slow calcite growth rates, yet PCP may be an important process at two intermediate drip sites during drought. Geochemistry of intermediate drip waters at IS is likely controlled by water supplied by conduit and matrix flow and may provide the preferred speleothem record for reconstructing past droughts in central Texas using trace-elements ratios. Flow-route characteristics of drip sites at other caves that may be expected to show drought response in terms of trace elements include drip rate response to changes in moisture conditions but relatively low drip rate coefficient of variation and sub-equal matrix- and conduit-flow contributions. The monitoring of key geochemical and physical parameters at a range of sites in a given cave may allow for the identification of speleothems that are most likely to be geochemically responsive to changes in climate, making the speleothem sampling process more informed and less destructive.Item The use of trace elements in correlating Rhyolitic lava flows(Texas Tech University, 1963-08) Cayce, Powers WilliamTrace elements in the feldspar pheocrysts from 12 layers of extrusive rhyolite and trachyte located in the central and north portions of the Davis Mountains, Trans-Pecos Texas, were analyzed spectrographically. Qualitative analyses using the d-c arc method revealed that the following elements were present in detectable quantities and were suitable for quantitative analysis: gallium, lithium, nickel, lead, scandium, yttrium, zinc, and zirconium. These elements were analyzed quantitatively using the internal standard method in conjunction with a 2.0:1 step-sector disc. Copper 3247.5 was chosen as the most suitable internal standard line because of its proximity to the other lines examined in this investigation. The emulsion was calibrated and working curves were constructed for the elements under consideration. The analyses show differences in the average content of gallium, lithium, nickel, lead, scandium, yttrium, zinc, and zirconium which may aid in correlating outcrops of the extrusive volcanic rocks, and thereby help in interpreting the geologic structure of the area. The average trace element content of at least two samples from the same flow, and more if possible, must be used before the numbers will be significant and become useful correlation tools. The analytical results presented here are preliminary. Analyses of many additional samples, combined with filed and petrographic studies, will be needed to establish the trends indicated, their mineralogical relationships, and their geologic significance.Item Trace element incorporation in modern speleothem calcite and implications for paleoclimate reconstruction(2014-12) Hatch, Rosemary; Banner, Jay L.Trace element compositions, expressed as ratios relative to Ca (Mg/Ca, Sr/Ca and Ba/Ca), in drip water and modern speleothem calcite were measured at multiple sites within a single cave system (Natural Bridge Caverns) in central Texas. These measurements are used to investigate how water and calcite compositions respond to changes in climate. Drip water trace element ratios respond to changes in climate and in soil, vadose zone and/or in-cave processes, which are in turn influenced by climate. It is commonly assumed that speleothem calcite directly reflects these changes in the drip water composition. To test this assumption, this study quantifies the partitioning of trace elements into speleothem calcite in a natural cave setting. To determine the controls on calcite trace element ratios, empirical partition coefficients (K [subscript D]) for Mg, Sr, and Ba are measured using a unique time series of water and modern calcite geochemistry at two drip sites. One drip site, dominantly supplied by conduit flow, has relatively invariant calcite trace element compositions that reflect correspondingly small variations in drip water chemistry. A second drip site, supplied by a combination of conduit and diffuse flow, exhibits a seasonal change in drip water composition due to changes in cave-air CO₂ concentrations. The drip water seasonality at this site is recorded in the calcite trace element compositions; however the partitioning of Mg/Ca from drip water to calcite is not controlled by the same mechanism(s) that control Sr/Ca and Ba/Ca partitioning. Results of this study indicate that the partitioning of Mg changes with drip water Mg concentration, temperature and location of the calcite relative to the point of drip impact. Calcite Sr/Ca and Ba/Ca ratios are more strongly influenced by changes in cave-air CO₂ that cause changes in CO₂ degassing, affecting calcite precipitation. This element specific partitioning complicates the interpretation of speleothem trace element records, since calcite Mg/Ca and Sr/Ca may not always covary even at drip sites that experience PCP. Although there is a strong correlation between Mg/Ca and Sr/Ca ratios in the drip water at these sites, there is considerable scatter between these two values in calcite. Average K [subscript D] values at both sites fall within the range of previous theoretical and empirical studies and are 0.025, 0.12 and 0.15 for Mg, Sr and Ba respectively. It is important to note that not all trace element partitioning is controlled by the same mechanism, since this has implications for interpretations of hydrologic processes from speleothems.Item Trace Elemental Variation in Dosidicus Gigas Statoliths Using LA-ICP-MS(2012-08-24) Arbuckle, Nancy 1980-Range expansion events of the Humboldt squid reveal our inadequate understanding of populations of this species. Despite recent hatching, reproductive, tagging, genetic and dietary studies of Dosidicus gigas, much speculation remains concerning geographic migration, stock assessment and habitat preferences. This study provides evidence that statolith trace elemental variations can be useful in distinguishing among geographic populations. Specimens were collected from the Galapagos Islands, southern California, and Washington State. A dissection method was recorded and published. By using laser ablation methods, discrete measurements of 10 elements were collected at 6 to 7 ablation sites covering embryonic, paralarval, juvenile and adult stages. Analysis of Variance revealed important ontogenic elemental variations among ablation locations. Multivariate Analysis of Variance, ordination techniques and discriminant function analysis with permutation testing were all utilized to compare and characterize the variations found in elemental concentrations. Significant ontogenic variations were found for 8 out of the 10 focus elements; this is the first report for 5 of these elements for this species. The geographic populations were effectively classified as distinct group for the first time using these methods. Elemental fingerprint signatures were found to be significantly different at multiple ontogenic growth regions of the statolith. Seattle and California paralarvae exhibited similar elemental signatures despite significant differences in those found in the embryonic core and juvenile regions of the statolith. These methods are a useful tool in providing stock assessment and can be improved for use in future population dynamics models.