Physical Sciences and Mathematics Commons^™

Characterizing Silicate Materials Via Raman Spectroscopy And Machine Learning: Implications For Novel Approaches To Studying Melt Dynamics, Blake O. Ladouceur

Doctoral Dissertations

Silicate melt characteristics impose dramatic influence over igneous processes that operate, or have operated on, differentiated bodies: such as the Earth and Mars. Current understanding of these melt properties, such as composition, primarily comes from investigations on their volcanic byproducts. Therefore, it is imperative to innovate on modalities capable of constraining melt information in environments where a reliance on laboratory methods is severed. Recent investigations have turned to Raman Spectroscopy and amorphous volcanics as a suitable pairing for exploring these ideas. Silicate glasses are a proxy for igneous melts; and Raman spectroscopy is a robust analytical technique capable of operating …

Utilizing Phylogenetic And Geochemical Techniques To Examine Echinoderms Through Time, Maggie Ryan Limbeck

Doctoral Dissertations

Understanding biotic changes through Earth’s history has been the goal of paleobiology since the inception of the field. Advances in science and technology have progressed allowing us to reassess old questions and new questions that could have not been addressed without these new methods. Echinoderms (sea stars, sea urchins, etc.) appear in the fossil record during the early Cambrian and are still abundant in marine ecosystems today. This persistence through time has made echinoderms model organisms to answer questions about Earth’s past and present. Despite this role as a model organism there are many questions that remain with respect to …

Metagenomic Investigation Of Microbial Dark Carbon Fixation, Viral Interactions, And Horizonal Gene Transfer Within A Convergent Margin Subsurface Ecosystem, Timothy Joseph Rogers

Doctoral Dissertations

Convergent margins are geological regions where two or more tectonic plates collide, and the denser “subducting slab” is pushed beneath the less dense overriding plate. As the slab descends, it devolatilizes under higher temperatures and pressures, allowing dissolved inorganic carbon (DIC) and redox active volatile rich fluids to cycle between the upper crust and Earth’s mantle. These fluids migrate through cracks and fissures in the upper mantle and crust, fueling chemolithoautotrophy-based microbial ecosystems in the subsurface before they are expelled on the surface in the form of hydrothermal seeps and springs. Chemolithoautotrophic ecosystems, such as those in the Costa Rican …

Numerical And Experimental Constraints On Trace Element Fractionation During Lunar Magma Ocean Solidification, Dian Ji

Masters Theses

Traditional lunar magma ocean (LMO) theory suggests the anorthositic lunar crust formed by floating of buoyant plagioclase, one of the major products of LMO solidification, on the surface of LMO. To test this model, after applying experimentally determined LMO solidification sequences, we compared calculated Rare Earth Element (REE) concentrations of lunar plagioclase to plagioclase in Apollo ferroan anorthosites and lunar anorthositic meteorites. Several initial LMO compositions, and lunar-relevant mineral-melt partition coefficient predictive models were tested (where the partition coefficient is the concentration ratio of a specific element between two phases). Compared with plagioclase in the natural samples, modeled plagioclase directly …

Evaluating Bulk Carbon And Nitrogen Isotope Compositions Of Acidic Hydrothermal Sediments On Earth– Implications For Mars Astrobiology, Chance Sturrup

Masters Theses

Carbon isotopes have been widely used as unique biosignatures because biologic processes commonly result in distinctive negative delta ¹³C values (-35 to -10 ‰) within organic material on Earth. However, the bulk delta ¹³C analysis in Gale crater sediments on Mars revealed a wider range of values, from -25 to +56 ‰ (Franz et al., 2020), which suggests a more complex origin. To determine if bulk isotope analysis can be successfully used to detect a microbial signature in a martian analog environment, we analyzed concentrations and isotope compositions of C within hydrothermal sediments in Iceland (Námafjall, Krýsuvík, Hveragerdi) …

Geochemical And Climatic Controls On The Sulfur Cycle In Volcanic Settings: Implications For The Origin Of Sulfur-Rich Deposits Investigated By The Spirit And Opportunity Rovers On Mars, Rhianna D. Moore

Doctoral Dissertations

On Earth, volcanic activity with elevated sulfur (S) degassing in the presence of water leads to the formation of hydrothermal deposits enriched in S-bearing minerals. Similar processes may have been an important source of S on Mars. The landing sites of Gusev crater and Meridiani Planum investigated by the Spirit and Opportunity rovers, respectively, showed elevated SO₄^2- [sulfate] concentrations, suggesting high- and low-temperature aqueous processes. However, the SO₄^2- contribution from subsequent aqueous weathering of hydrothermal S deposits has been poorly constrained, thus its importance to regional S cycling in the landing sites is unclear. In this …

Natural, Experimental, And Educational Explorations Of The Interiors Of Terrestrial Planetary Bodies, Nadine L. Grambling

Doctoral Dissertations

Planetary interiors are enigmatic, inaccessible, and vital to the processes that have formed the rocks we see on the surface of bodies in the inner Solar System today. Based on geophysical explorations of the Moon and Earth, along with information gleaned from rocks at the surface today, there is understanding of the basic structure and processes at depth. Using a combination of natural samples and experimental studies, we attempt to learn more about the physical conditions beneath the surface, and their effect on material properties and tectonics processes in the mantle.

On Earth, mid-ocean ridge processes have long been debated, …

Experimental Approaches To Evaluating Silicate Melt Properties And Trace Element Fractionation During Crystallization At High Pressures And High Temperatures, Megan D. Mouser

Doctoral Dissertations

Current understanding of the evolution and behavior of silicate materials that form in planetary interiors at high-pressures and high-temperatures largely come from experimental work as natural samples are either rare, or physically inaccessible. Laboratory experiments provide a comprehensive way to constrain the crystallization history, elemental partitioning, and viscosity of different silicate materials at planetary mantle pressure and temperature conditions. This work utilizes two high-pressure experimental techniques, the Paris-Edinburgh apparatus, and the piston cylinder apparatus, to measure physical and chemical properties of silicate materials. The viscosity of reduced, Fe-free silicate liquids, with and without sulfur (S-free and S-bearing), were measured to …

Precambrian Molar-Tooth Structure: Unraveling The Diagenesis Of Ancient Carbonates, Agustin Kriscautzky

Doctoral Dissertations

Molar-tooth structure (MTS) is an enigmatic carbonate fabric that occurs mainly within Proterozoic carbonate host rocks. It is composed of two distinct features: cracks of various morphologies and crack-filling calcite microspar. Although the origins of MTS remain unknown, most previous investigation has focused on the formation of the cracks and mechanisms involved in the void space generation, with less emphasis on the intriguing carbonate fill. In this study I have investigated molar-tooth bearing carbonates from regions that span both paleogeography and geologic time. Analysis at the microscopic scale, including traditional petrography, cathodoluminescence petrography, scanning electron microscopy, and micrometer-scale geochemical analyses …

Influence Of Physical Variability Of Highly Weathered Sedimentary Rock On Nitrate In Area 3 Of The Enigma Field Research Site At Y-12, Erin Kelly

Masters Theses

Uranium processing and waste storage in unlined waste ponds leached contaminants into the groundwater at Y-12, Oak Ridge, Tennessee, from the 1950s to 1980s. Groundwater wells near the S-3 ponds have had the highest nitrate concentrations of groundwater anywhere in the world (>10,000 mg/L). For reference, the maximum contaminant level for nitrate in drinking water set by the U.S. Environmental Protection Agency is 10 mg/L. Since 2012, the ENIGMA (Ecosystems and Networks Integrated with Genes and Molecular Assemblies) group has been characterizing, monitoring, and conducting field experiments to understand the interactions between contaminants, microbes, and the subsurface. The goals …

Experimental Alteration Of Venusian Surface Basalts In A Hybrid Co2-So2 Atmosphere, Robert B. Reid

Masters Theses

Venus’ surface and interior dynamics remain largely unconstrained, due in great part to the major obstacles imposed by its 470°C, 90 bars surface conditions and its thick, opaque atmosphere. Orbiter-based thermal emission data provide an opportunity to characterize the Venus surface. However, interpretations of such spectra critically depend on understanding interactions between the planet’s surface basaltic rocks and its caustic, SO₂-bearing CO₂ atmosphere. Several studies, using remote sensing, thermodynamic modeling, and laboratory experiments have placed constraints on alteration mineralogies and rates. Yet constraint with respect to SO₂-mediated reactions with basalts of contrasting compositions remains incomplete. …

Carbon Metabolism In Cave Subaerial Biofilms, Victoria E. Frazier

Masters Theses

Subaerial biofilms (SABs) grow at the interface between the atmosphere and rock surfaces in terrestrial and subterranean environments around the world. Multi-colored SABs colonizing relatively dry and nutrient-limited cave surfaces are known to contain microbes putatively involved in chemolithoautotrophic processes using inorganic carbon like carbon dioxide (CO₂) or methane (CH₄). However, the importance of CO₂ and CH₄ to SAB biomass production has not been quantified, the environmental conditions influencing biomass production and diversity have not been thoroughly evaluated, and stable carbon and nitrogen isotope compositions have yet to be determined from epigenic cave SABs. …

Fire-Vegetation-Climate Interactions Across The Holocene On The U.S. Southeastern Coastal Plain, Mathew S. Boehm

Doctoral Dissertations

This dissertation research examined multiple proxy indicators in sediment cores from one lake and one wetland to reconstruct long-term relationships between fire, vegetation, and climate in the southeastern U.S.

At Lake Balboa (30.6992 N, 83.2031 W; 48 m elevation), a sinkhole pond located in southern Georgia, Bølling-Allerød conditions were sufficiently wet to maintain a shallow wetland at the site. Evidence for fire was minimal. Between 12,600 and 9200 cal yr BP, water availability declined, leading to a potential hiatus in sedimentation. During the early Holocene moisture availability increased, leading to greater primary productivity within and outside the lake, triggering an …

Structure And Adsorption At The BastnäSite-Water Interface: Fundamental Investigations Toward Rare Earth Mineral Recovery, Anna Kristiina Wanhala

Doctoral Dissertations

This dissertation investigates the interfacial structure and reactivity of a rare earth mineral in the context of froth flotation. Bastnäsite [(Ce,La,Nd)FCO3], one of the primary mineral sources of rare earth elements, has been chosen for this investigation. Flotation separation relies on selective adsorption of collector ligands to the desired mineral surface in solution; fundamental understanding of these adsorption reactions will aid in the development of more effective separation technologies.

Chapter 1 presents an introduction to the significance of rare earth minerals and the process of froth flotation. Chapters 2 and 3 address the adsorption reactions of ligand molecules at the …

High-Resolution Timeseries Analysis Of Dynamic Geochemistry: A 27-Well Survey Of Contaminated Groundwater Downstream Of The Former S-3 Ponds, Oak Ridge, Tennessee, Emma Dixon

Masters Theses

Spatiotemporal variability of geochemistry of contaminated groundwater has large implications on overall water quality and ability to respond to remedial applications. Gaining knowledge of how geochemistry changes over time in an area can help establish response trends to changing external conditions like weather and level of contamination. In this study, a spatiotemporal survey was performed on 27 wells at the Y-12 Complex in Oak Ridge, Tennessee. This was completed to measure diurnal fluxes in geochemistry from seasonal changes and extreme weather conditions in three areas of historically different contamination levels from a single point contamination source. Measurements were gathered over …

Development Of Nuclear Underground Engineered Test Surrogates For Technical Nuclear Forensics Exploitation, Robert Boone Gilbreath

Masters Theses

A method for formulation and production of Nuclear UnderGround Engineered Test Surrogates (NUGETS) based on notional improvised nuclear device (IND) detonations in an underground environment analogous to the Nevada National Security Site (NNSS) is presented. Extensive statistical analyses of precursory geochemical and geophysical characteristics are combined with an augmented surrogate debris cooling technique and predictive IND contributions from the ORIGEN Fallout Analysis Tool. Precursory and resultant elemental compositions, cooling curve calculations, and visual comparison of NUGETS to genuine underground debris are reported. Application of NUGETS methodology to future studies in urban, underground post-detonation technical nuclear forensic (TNF) analysis is suggested.

Determining Sources Of Nitrate In The Semi-Arid Rio Grande Using Nitrogen And Oxygen Isotopes, Diego Alberto Sanchez Hernandez

Masters Theses

The Rio Grande, a semi-arid river in the American Southwest, is a major source of surface water for agriculture and drinking supplies in New Mexico and Texas. In addition to increasing salinity, considerable increases of NO₃^- [nitrate] have been observed in the semi-arid portion of the Rio Grande. It is possible that elevated water salinity inhibits denitrification on irrigated fields and, thus, fails to mediate excess nutrient load from anthropogenic activities. Therefore, two major goals of this project were to 1) characterize and quantify major NO₃^- sources, and 2) assess whether elevated water salinity affects microbial …

Role Of Sorting On The Composition Of Siliciclastic Sediment: Implications For Interpreting Provenance After Limited Transport In An Arid Climate, Forrest Christopher Driscoll

Masters Theses

This study tested whether transport distances (< 500 m) have the capacity to shape the geochemistry of sediments across multiple grain-size populations due to sorting derived from a single source. In the Stepladder Mountains, Mojave Desert, CA, a < 1 km² [square kilometers] watershed allows for a controlled study to understand how modern sediments acquire their composition from a single granodioritic source in an arid climate where there is no chemical weathering. Sediments are naturally sorted into distinct grain-size populations, with modes ranging from very fine sand to gravel within a single, alluvial channel. Sediment samples representative of each population were petrographically and geochemically analyzed in order to test the effectiveness of commonly used discrimination diagrams. Sediments became proportionally enriched in plagioclase and biotite and depleted in K-feldspar and quartz with decreasing grain …

Environmental Controls On The Diversity And Distribution Of Endosymbionts Associated With Phacoides Pectinatus (Bivalvia: Lucinidae) From Shallow Mangrove And Seagrass Sediments, St. Lucie County, Florida, Thomas Walters Doty

Masters Theses

Lucinid bivalves are capable of colonizing traditionally inhospitable shallow marine sediments due to metabolic functions of bacterial endosymbionts located within their gills. Because lucinids can often be the dominant sediment infauna, defining their roles in sediment and pore fluid geochemical cycling is necessary to address concerns related to changes in coastal biological diversity and to understanding the sensitivity of threatened coastal ecosystems over time. However, there has been limited research done to understand the diversity and distribution of many lucinid chemosymbiotic systems. Therefore, the goals of this thesis were to evaluate the distribution of Phacoides pectinatus and its endosymbiont communities …

Experimental Limestone Dissolution And Changes In Multiscale Structure Using Small- And Ultra Small- Angle Neutron Scattering, Chad Alan Novack

Masters Theses

Small angle neutron scattering (SANS), ultra-small angle neutron scattering (USANS), and backscatter electron (BSE) imaging, along with neutron computed tomography (NCT) were used in this study to experimentally quantify pore size, distribution, and connectivity of dissolved limestone geometries. Eight samples of Indiana limestone of two different initial permeabilities (2-4 mD and 70 mD ) [millidarcy] were reacted with HCl [hydrochloric acid] solutions at differing pH (2 and 4), and flow rates (0.1 and 10 cm³/min) [cubic centimeters per minute] to describe a broad range of parameters that affect limestone dissolution. NCT was first used to image the dissolution …

Examination Of Banded Iron Formation Through Petrographic, Geochemical And Iron Isotope Analyses, Melissa Margaret Hage

Doctoral Dissertations

Banded iron formation (BIF) has the potential to preserve geochemical signatures critical to interpretation of early Earth because: (1) it is found within the Precambrian when fundamental changes in Earth’s physical, biological and chemical evolution occurred, and (2) it may preserve a record of the depositional environment. Rare earth elements (REE) are useful for investigating BIF because they have characteristic features. One goal of this study was to evaluate the calculation of certain REE ratios to determine if the calculation affected the interpretation. It was concluded that the method for calculating certain ratios may affect the interpretation of redox conditions …

Evidence Of Late Quaternary Fires From Charcoal And Siliceous Aggregates In Lake Sediments In The Eastern U.S.A., Joanne P. Ballard

Doctoral Dissertations

The late-glacial transition to the Holocene, 15,000–11,600 cal yr BP, is an enigmatic period of dynamic global changes and a major extinction event in North America. Fire is an agent of disturbance that transforms the environment physically and chemically, and affects plant community composition. To improve understanding of the linkages between fire, vegetation, and climate over the late glacial and Holocene in the eastern U.S., I analyzed lake-sediment cores for charcoal and indicators of wood ash, and compared results to existing pollen records. A new microscopic charcoal record from Anderson Pond, Tennessee revealed high fire activity from 23,000–15,000 cal yr …

Timing And Extent Of The Little Ice Age Glacial Advances In The Eastern Tian Shan, China, Yanan Li

Doctoral Dissertations

Located in Central Asia, one of the most continental regions on Earth, the Tian Shan’s glaciers contribute critical fresh water to populated areas in the lowland. These glaciers are sensitive to climate change, and knowledge of contemporary glaciers and their changes in the past is of critical importance for sustainable development in this region. Constraining glacial fluctuations in recent centuries will fill a gap in numerical constraints on glacial history and paleoclimate information, and provide important evidence on the spatio-temporal changes of the climate systems in the Tian Shan. This doctoral dissertation investigates the timing and extent of Little Ice …

Distinguishing Primary Versus Secondary Geochemical And Silicon Isotope Characteristics Of Precambrian Chert And Iron Formation, Latisha Ashley Brengman

Doctoral Dissertations

Precambrian chert and banded iron formation (BIF) are defined as chemical sediments precipitated directly from seawater. As such, their geochemistry, including trace elements, rare earth elements (REE), and isotopes (O, Si) may preserve Precambrian seawater conditions. However, the chemical signature of these rocks may not simply reflect seawater, because hydrothermal interactions and metasomatism may produce rocks that petrographically and chemically resemble chert and BIF, including seawater-like compositional characteristics acquired during mineral replacement. Interpreting the major-, trace-, and rare-earth element signatures of these rocks requires the identification of geochemical and isotopic fingerprints that differentiate rocks formed from chemical sedimentation from rocks …

Characterizing Groundwater Ch4 And 222rn In Relation To Hydraulic Fracturing And Other Environmental Processes In Letcher County, Ky, St. Thomas Majeau Ledoux

Masters Theses

Hydraulic fracturing of shale deposits has greatly increased the productivity of the natural gas industry by allowing it to exploit previously inaccessible reservoirs. However, previous research has demonstrated that this practice can contaminate shallow aquifers with CH₄ [methane] from deeper formations. This study compares concentrations and isotope compositions of CH₄ sampled from domestic groundwater wells in Letcher County, Kentucky in order to characterize its occurrence and origins in relation to neighboring hydraulically fractured natural gas wells. Additionally, this study tests the reliability of ²²²Rn [radon] as an alternative tracer to CH₄ in identifying processes of gas …

Exploring Martian Magmas: From The Mantle To The Regolith, Arya Sigrid Waltraud Udry

Doctoral Dissertations

The planet Mars is geologically more similar to Earth than to other planets of the solar system. For the past 50 years, new rovers, orbital spacecraft, and new martian meteorites have helped us to understand the geological processes that occurred on Mars. In this dissertation, I investigate a wide range of martian igneous compositions, such as shergottite and nakhlite meteorites, Gusev and Gale surface basalts, and the Northwest Africa (NWA) 7034 breccia. I attempt to better understand magmatic processes that occurred in the martian mantle and crust as well as surficial processes using various petrologic and geochemical tools.

As shown …

Mineralized Microbialites As Archives Of Environmental Evolution Of A Hypersaline Lake Basin: Laguna Negra, Catamarca Province, Argentina, Joy Buongiorno

Masters Theses

Environmental fluctuations related to climate, biological productivity, and evaporation can be recorded by sedimentary archives within lacustrine depositional systems. Sediments within terminal, closed-basin lakes are amongst the most sensitive paleoenvironmental indicators, and have great potential for permitting detailed reconstruction of environmental conditions via a variety of geochemical and isotopic proxies. Microbialites, however, have been largely overlooked as repositories of paleoenvironmental data. Here, we investigate mineralized microbialites within Laguna Negra, a high-altitude (4100 meters above sea level) hypersaline, closed-basin lake in the Argentinian Puna region and explore the potential recovery of environmental signals from these unique sedimentary archives. Mineralized microbialites within …

Characterizing The Relationship Of Part Of The Inner Piedmont And Pine Mountain Window, Georgia, From Detailed Geologic Mapping, Geochemistry, Geochronology, And Structural Analysis At The Southwestern End Of The Cat Square Terrane, Justin Randolph Rehrer

Masters Theses

Geologic investigations at the southwestern end of the Cat Square terrane (CSt) in central Georgia provided new insight into the complex tectonic history of the Pine Mountain window (PMw) and neighboring Inner Piedmont terranes. Detailed 1:24,000-scale geologic mapping of an approximately 180 km2 area near Barnesville, Georgia has provided the foundation for further geochemical, geochronologic, and structural analyses refining models for tectonic development and emplacement of the CSt and PMw.

Whole-rock geochemical analyses of several CSt amphibolites yielded data suggesting a continental back-arc setting for genesis of the Cat Square basin (CSb). Major element data confirm derivation from a basaltic …

Calcitized Evaporites In The Precambrian: Deposition And Diagenesis In A Low Sulfate Ocean, Ashley René Manning Berg

Masters Theses

One of the most profound byproducts of the Great Oxidation Event (GOE) was the onset of oxidative weathering on land and the riverine delivery of sulfate to marine systems. The marine sulfur system therefore plays a critical role in reconstructing the oxygenation of the early Earth. Although the exact nature of marine oxygenation in aftermath of GOE remains uncertain, examination and modeling of marine sulfate suggest that sulfate concentrations remained below 2 millimolar (mM) until at least the middle Mesoproterozoic, and may have only reached about 10 mM in the latest Neoproterozoic. Such a low concentration of marine sulfate had …

Gastrointestinal Microbial Diversity And Diagenetic Alteration Of Bone From The American Alligator (Alligator Mississippiensis), Sarah Wheeler Keenan

Doctoral Dissertations

One of the most challenging questions in paleobiology is how bone transforms from a living tissue into a fossil. In life, the gastrointestinal tract microbiome of an animal promotes host health. But, in death, these microbial communities, as well as soil communities, begin to degrade tissue, including bones. Using the American alligator from coastal wetland habitats as a model system, the gastrointestinal tract microbiome was found to contain microbial communities consisting of Fusobacteria, Proteobacteria, Bacteroidetes, and Firmicutes, with variations based on tissue type along the length of the digestive tract. The overall dominance of Fusobacteria is distinct from any other …