Some of the material in is restricted to members of the community. By logging in, you may be able to gain additional access to certain collections or items. If you have questions about access or logging in, please use the form on the Contact Page.
Some of the material in is restricted to members of the community. By logging in, you may be able to gain additional access to certain collections or items. If you have questions about access or logging in, please use the form on the Contact Page.
After decades of research biogeochemists have identified several intervals of variable marine oxygenation throughout Earth's history. These fluctuations in oxygenation have been proposed to directly correlate to changes in ancient...
To better constrain the timing of panda's dietary shift from omnivorous to bamboo-exclusive herbivores, this study analyzed stable isotopes of carbon and oxygen in tooth enamel samples from two pygmy pandas from Yanliang Cave (early...
URANIUM-SERIES NUCLIDES IN SEDIMENTS AND PHOSPHATE NODULES FROM THE PERUVIAN CONTINENTAL MARGIN (RADIUM, BIOTURBATION, PHOSPHORITE)
Description:
Uranium-series disequilibrium techniques have been applied to sediments and phosphate nodules sampled from the Peru-Chile continental margin in order to decipher growth histories of the nodules and time scales of diagenetic processes... Uranium-series analysis of 11 series of contiguous slices from individual phosphate nodules consistently show unidirectional growth at rates of 0.1 to 10 mm/Kyr with a trend of slow but persistent radium leakage with time. Estimated... Growth curves based upon ('226)Ra and ('230)Th radiometric ages of sequential layers in a buried phosphate crust show that this crust grew upward toward the sediment-water interface at a rate of 12-13 mm/Kyr. Crystallographical analyses... An intercomparison of uranium-series and ('14)C ages of 9 phosphorite samples show that both methods agree reasonably well with each other for samples younger than 30 Kyr. A pelletal phosphorite displayed the greatest discrepancy between... A radiochemical study of sediments associated with these phosphorites produced ('210)Pb-derived sedimentation rates on the order of a few mm/yr in the vicinity of the most intense upwelling (12(DEGREES)S and 15(DEGREES)S) decreasing by a...
The study conducted U-Pb isotopic dating of the pitchblende mineralization of the Coles Hill uranium deposit in Pittsylvania County, VA. The ore body is found along the Chatham fault and within the Martinsville Igneous Complex. In...
MINERAL, CHEMICAL AND TEXTURAL VARIATIONS ALONG S-SURFACES IN SELECTED OUTCROPS OF AMPHIBOLITE, GEORGIA AND ALABAMA PIEDMONT
Description:
Amphibolites were systematically sampled along s-surfaces from two outcrops in the Alabama and Georgia Piedmont. S-surfaces are planar features that pervade rocks. In this study the s-surfaces have a metamorphic origin. Compositional and... Chemical variations between s-surfaces show chemical differentiation that could have been present in an original basaltic body. The s-surfaces are oriented at oblique angles to the direction of inferred differentiation in both outcrops.... The major mineral transformation recorded in these rocks is plagioclase changing to clinozoisite. The degree of this mineral reaction varies along s-surfaces. The dependence of this reaction on the presence of water indicates that fluid... Hornblende crystals that were originally more randomly distributed have rotated and translated to a less random arrangement due to the volume decrease that accompanied the retrograde plagioclase-clinozoisite reaction. This study includes the most detailed quantitative description of metamorphic rock textures thus far described in the literature. Quantitative textural parameters include the distribution of hornblende and clinozoisite in the rock, ... The textural values obtained from amphibolites in Alabama and Georgia are comparable to those of amphibolites from New Mexico, Scotland and Wyoming. Therefore, regardless of variations of metamorphic grade and degrees of strain, ...
The major elements, trace elements, and isotopic composition of clinopyroxene and garnet fractions from mantle xenoliths from Colorado Plateau area were analyzed in this study to examine the sources of the xenoliths and their role in...
Characterization of sedimentary organic matter from the Florida Everglades by inverse gas chromatography and solid state carbon-13 NMR spectroscopy
Description:
Solid state $\sp{13}$C NMR, Inverse Gas Chromatography and elemental analysis have been used to study the early diagenesis of organic matter of peat deposits from the Florida Everglades and to develop correlations between the structure... The structure of the sedimentary organic matter and its fraction was studied by solid state $\sp{13}$C NMR cross polarization and dipolar dephasing NMR experiments. The changes in the different polar, aliphatic and aromatic groups are... $\sp{13}$C NMR and elemental analysis of the sediments indicate that the carbohydrate is selectively degraded while aromatic structures were preserved. The structure of the organic matter becomes more reduced and crosslinked with age. IGC was used to evaluate relative affinity of these peats and their fractions for a number of selected non-ionic organic compounds. The different fractions of the organic matter were used as stationary phases and non-ionic organic...
Experimental and theoretical investigation of radiation-induced, electron paramagnetic resonance-detected point defects in quartz: Implications for geochronometry
Description:
Consideration is given to the premise that certain electron paramagnetic resonance signals in natural quartz are the result of age-indicative accumulations of alpha recoil-induced lattice damage. The point defects potentially responsible... Theoretical considerations involve factors related to (1) recoil damage efficiency, (2) paramagnetic fractions of precursor defect populations, (3) overlap of alpha recoil track volumes and (4) fluid inclusion-hosted alpha activity. It...
The Late Miocene brought a sudden increase in the biomass of C4 plants that resulted in an expansion of grassland habitat and markedly changed the diets of vertebrate fauna in many places around the world. Concurrently, early pulses of...
Trace metal biogeochemistry in the Black Sea: Dissolved and suspended-particulate chemical fractionation of transition and Class B metals
Description:
The solution speciation and solid-phase suspended particulate fractionation of the trace metals Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb were investigated in the Black Sea, the world's largest anoxic basin. Sequential filtration/ion... The Class B metals (Cu, and Pb) were high in the surface waters and decreased rapidly across the sulfide interface, consistent with metal-sulfide precipitation below the interface. The dissolved metal fractionation was dominated... With the exceptions of Al and Fe, the suspended matter trace metal fractionation was dominated by weak-acid soluble forms. Strong-acid leachable forms, probably metal-sulfide phases, were important in the deep waters for Mn, and Co.
Alteration effects associated with Mesozoic diabase intrusives and their host rocks in rift basins from Maryland and Virginia
Description:
Mineralogical and geochemical effects of alteration were studied in three early Mesozoic diabase/host-rock systems: (1) the Rocky Ridge dike and aureole, Gettysburg basin, Maryland; (2) the West Gainesville and Nokesville diabase sheets... Observed mineral reactions in the diabase are consistent with relative mobilities; the dominant mechanisms for this mass transfer are apparently infiltration metasomatism and intergranular diffusion. Relative mobilities of cations can be...
Lake Jackson in Leon County Florida is a shallow perched dissolution lake, which sits above the Cody Scarp and is formed from the coalescence of sinkholes. Lake Jackson currently has two open sinkholes, Porter Sink and Lime Sink....
URANIUM-LEAD, RUBIDIUM-STRONTIUM, AND POTASSIUM-ARGON ISOTOPIC STUDIES BEARING ON THE TECTONIC DEVELOPMENT OF THE SOUTHERNMOST APPALACHIAN OROGEN, ALABAMA
Tracing groundwater flow into the northeastern Gulf of Mexico using a naturally occurring radon-222
Description:
Submarine groundwater discharge and recirculated seawater may provide important chemical constituents to the ocean, but the dispersed nature of this process makes locating and quantifying its input difficult. Two approaches were taken to... The response of seepage meters to water motion effects was evaluated in the nearshore study area through time-series experiments using empty and 1000-mL prefilled collection bags. It was confirmed that prefilling the plastic bags... Concentrations of $\sp{222}$Rn in groundwater are 3 to 4 orders of magnitude higher than seawater. Integrated concentrations in the nearshore waters overlying a seepage meter transect showed a significant positive relationship to direct... Factors influencing the concentration of radon in the inner continental shelf waters (i.e., production-decay, horizontal transport, and benthic advection and diffusion) were evaluated using a linked benthic exchange-horizontal transport...
Understanding the chemical and biological innovation and evolution of the global ocean is pivotal in understanding the processes involved in the evolution and proliferation of early life on Earth and potentially habitable exoplanets....
A geochemical and strontium isotopic investigation of Laramide and younger igneous rocks in central Colorado, with emphasis on the petrogenesis of the Thirtynine Mile volcanic field. (Volumes I and II)
Description:
New and existing geochemical and Sr-isotopic data are used to characterize the composition and time-space distribution of Laramide and younger calc-alkaline to alkaline igneous rocks in central Colorado. The study is focussed on the $... Geochemical and Sr-isotopic evidence confirms tuff occurrences in the southern Denver basin are Wall Mountain Tuff ($\sim$36.7 Ma). Previous suggestions that the Wall Mountain Tuff is closely related to the Mount Princeton batholith are...
Oceanic core complexes (OCCs) are the uplifted and rotated footwalls of detachment faults formed at areas of slow spreading on mid-ocean ridges. Detachment faults initiate close to the spreading axis, and because it is easier to continue...
THE POTENTIAL ORIGIN OF THE POTASSIUM DEPTH RELATIONSHIP IN THE BATAAN OROGENE, THE PHILIPPINES (ISLAND ARC, ANDESITE, PETROLOGY, ISOTOPES, BASALT)
Description:
Three classic volcanic arcs have developed in western Luzon, the Philippines as a result of subduction associated with an eastward-dipping Benioff zone. A data set for about 200 samples was determined for this and earlier studies. This... Based on these data, several conclusions can be made: (1) Excellent linear correlations exist between SiO(, 2) and the incompatible elements. The slopes of these trends increase progressively from western arc through the central to the...
Until the past decade, IIAB iron meteorites were thought to have formed by fractional crystallization under low pressure, corresponding to an asteroidal sized (<200 km) parent body. Some recent physical models for the formation of early...
Software packages that model geochemical speciation and complexation are useful for predicting how different materials such as heavy metals and organic matter interact with the environment. The East Fork Poplar Creek (EFPC) in Oak Ridge, ...
Panamá arc activity has been divided into three episodes, the Late Cretaceous to Eocene episode, the Miocene episode, and the Pliocene to recent adakite suite. Rocks from the oldest episode are dominantly hornblende bearing, contain a...
Competitive complexation studies of europium(III) and uranium(VI) complexation by aqueous orthosilicic acid
Description:
The environmental chemistry of actinide elements is of considerable interest since the release of actinides into the environment is considered the primary long-term hazard of nuclear waste disposal in geological repositories. While... Ligand competition experiments were employed to measure the stability constants of these f-element-orthosilicate complexes. Europium-orthosilicate complexation was studied by solvent extraction and laser-induced fluorescence spectroscopy... Speciation calculations show that europium orthosilicate complexes are important inorganic species for waters between pcH 6 and 7.5 that are in equilibrium with atmospheric carbon dioxide and contain at least 0.03 mM orthosilicate....
The Silurian was a period characterized by rapidly fluctuating climate, multiple biotic turnover events, and eustatic sea-level variability. The Homerian Mulde biotic event (late Wenlock), ~428Ma, lies between the Sheinwoodian (early...
This study investigates the effects of geological structure of the aquifers and the chemistry of water by testing the water chemistry variation such as the main cations (Na+, K+, Ca2+, Mg2+) and anions (Cl-, SO4 2-, HCO3 -) and TDS from...
The Greenland Ice Sheet (GrIS) is melting at an alarming rate. Supraglacial melt water flows into moulins that drain to the base of the ice sheet, and enhances basal flow. Ultimately, large quantities of melt water are expelled into the...
This thesis is focused on two aspects: one is to obtain high precision measurement of rhenium isotope composition of iron meteorites; the other is to discuss what processes cause systematic isotopic differences in Re between IVB irons...
Organic geochemical proxies (OGPs: δ13C, δ15N and C/N) preserved in coastal lake sediments appear to be more sensitive indicators of past storm events than traditional proxies used in paleotempestology. However, the method has not been...
The timing and mechanisms responsible for the expansion of C4 grasses have been a topic of considerable debate over the last two decades. Although abundant evidence indicates that there was a worldwide, rapid increase in C4 ecosystems ...
Patterns and rates of chemical evolution of groundwater near a sinkhole lake, northern Florida
Description:
To better understand the hydrochemical interaction between groundwater and lakewater in a mantled karst setting, a comprehensive study was conducted to determine the processes that control the patterns and rates of chemical evolution of... Groundwater downgradient of Lake Barco was anoxic, with elevated concentrations of hydrogen sulfide, ferrous iron, and methane, resulting from leakage of lakewater through reducing, organic-rich sediments at the bottom of the lake. Based... This research study has provided a framework for a better understanding of recharge processes and the importance of both abiotic (mineral dissolution and precipitation) and biotic (microbially mediated degradation of organic matter)...
The Panamanian Isthmus presents an ideal opportunity to study arc magmatism, arc-hotspot interaction, and the effects of the South America-Panama collision. These effects include changing mantle wedge compositions and localized tectonic...
Structural evolution and metamorphic petrogenesis of a metasediment and metaigneous complex, Coosa County, Alabama
Description:
Investigation of metasedimentary and metaigneous units of the northern Alabama Piedmont has revealed the following evidence: (1) stratigraphic continuity exists between previously uncorrelated lithotectonic blocks, (2) petrogenesis of... Analysis of micro-, meso- and megascopic structural relationships has revealed 5 phases of deformation. Previous investigations have established the internal stratigraphy of structural blocks composing the northern Alabama Piedmont. This...
THE MARINE GEOCHEMISTRY OF TIN (MONOBUTYLTIN, ESTUARIES, AEROSOL)
Description:
A geochemical cycle for tin through the marine system is proposed. The input fluxes from rivers and the atmosphere have been considered and the behavior of tin in the oceans has been investigated. An analytical technique has been developed that is sensitive enough to directly measure tin at the concentrations found in most areas of the environment without contamination or preconcentration. Detection limits are 50, 50 and 20... On the basis of measurements from a large number of rivers from pristine and polluted regions, we estimate the riverine fluxes of tin to the oceans to be 0.42 x 10('6) moles/year for the dissolved fraction and 320-960 x 10('6) moles/year... Atmospheric tin concentrations in the northern hemisphere are up to three orders of magnitude greater than those in the southern hemisphere, indicating the importance of anthropogenic inputs to the atmospheric tin cycle. Most of the... A large scale study of tin concentrations in seawater has revealed concentrations much lower than previously reported. Surface water concentrations are in the range of non-detectable (< 1.5 picomolar) to 16 picomolar. Almost all depth...
GEOCHRONOLOGY OF THE PRECAMBRIANS OF RAJASTHAN, INDIA
Description:
A geochronological investigation of the Precambrian rocks of Rajasthan, India, was undertaken to decipher the Precambrian geology of Rajasthan in general and the ages of the three episodes of granitization and metamorphism observed in... Discordant zircon ages from granites of the Precambrian rocks of Rajasthan suggest three periods of granitization. The ages of these three periods of granitization in ascending order are, 2600 m. y., 1700 m. y. and 800 m. y. Only 2600 m.... The 2600 m. y. old tectonic event which seems to be confined to the central Aravalli range in Rajasthan, probably the core of the Aravalli mountain, and dates the Aravalli regional tectonic event. The 1700 m. y. old regional tectonic event is recognized on a much wider area and dates the Delhi regional tectonic event. The granites of this period are either co-folded with the Delhi system of rocks or are post-Aravalli. The latest regional tectonic event in the Precambrian of Rajasthan is the 800 m. y. old "Erinpura" type event and it is post-Delhi and are represented by massive granitization especially in the southwestern part of Rajasthan (Mt. Abu). It appears that Malani rhyolites might have inherited some zircons from older rocks and a discordant zircon age of 863 m. y. obtained for these rhyolites is a maximum age for the Malani rhyolites. Zircons from three different granitic plutons plot on a discordia chord with a crystallization age of approximately 1680 m. y. and a lower intercept age of approximately 70 m. y. It also appears that the 800 m. y. old granitic plutons of...
Archaeological excavations in Florida have recovered numerous specimens of megafauna over the past decades. A sample of these specimens have been subject to carbon and oxygen stable isotope analysis to determine individual diet and water...
El Valle is the easternmost volcano in the Central American Volcanic Arc, and is characterized by two periods of volcanic activity, an Old Group from 10-5 Ma and a Young Group from 3-0.03 Ma. Both the Old and Young Group’s are calc...
The Dadeville Complex is a large klippe located in the Alabama Inner Piedmont of the southern Appalachian orogen lying immediately above rocks of the eastern Blue Ridge and Brevard Zone, in the core of the Tallassee synform. Structural...
Geochemical Proxies Preserved in Fossils and Lake Sediments: New Insights into Ancient Diets and Environments in South China and Storm Activity in South Florida
This dissertation research has used geochemical tools to reconstruct paleoecology and paleoenvironment with the goal to better understand the effects of long-term climate change on terrestrial ecosystems and mammalian evolution in South...
A STUDY OF URANIUM AND THORIUM ISOTOPES IN GROUND WATERS AND SOLIDS OF TWO URANIUM MINES, SOUTH TEXAS
Description:
Isotopic analysis was carried out on water and solid samples taken from both the ore zones and the general vicinity of two uranium mines in south Texas. The uranium deposits were of the roll-front type. The ore-bearing formations were... The integration of data from each of these models, including contour maps of various isotopic parameters and statistical plots helped in predicting the presence, the stage of deposition (dispersing, stable or accumulating) and the degree... The isotopic data were also useful in determining the position of the redox boundary and the environment of a sample. These methods may be useful in prospecting studies of other possible uranium deposits, both in the oxidized and/or the...
Stalagmites, or speleothems, are secondary cave deposits that record the isotope and trace element composition of the parent dripwaters within their crystal matrix. Changes in dripwater oxygen and carbon isotopes (δ18O and δ13C) and...
The chemical compositions of basaltic melts from diverse tectonic settings on Earth are interpreted in terms of mantle sources that are either a single lithology (peridotite) or composed of two mixed lithologies (peridotite + pyroxenite)...
Chondrules are silicate spherules in chondritic meteorites thought to have formed as free-floating melt droplets created by a transient heat source in the early solar system. Due to their ubiquity in asteroids, determining the origin of...
Some of the material in is restricted to members of the community. By logging in, you may be able to gain additional access to certain collections or items. If you have questions about access or logging in, please use the form on the Contact Page.
