Geology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2774
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Item GEOCHEMICAL INDICATORS OF REDOX AND WEATHERING ACROSS THE EDIACARAN-CAMBRIAN TRANSITION IN SIBERIA(2024) Doerrler, Andrew; Kaufman, Alan Jay; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The transition between the Ediacaran and Cambrian periods witnessed the fall of the enigmatic Ediacara biota. The cause of their extinction is poorly understood, but the timing broadly coincides with a significant negative ẟ13C anomaly, the BAsal Cambrian Carbon isotope Excursion (BACE). These macroscopic organisms were likely tolerant of anoxic conditions, so oceanic oxidation may have been a kill mechanism. This study utilizes uranium isotopes, sulfur isotopes, and cerium anomalies to understand oceanic redox conditions from two BACE sections in Siberia, as well as lithium isotopes to constrain weathering intensity. Reconstruction of seawater ẟ238U values from equivalent evaporite and carbonate-dominated successions indicate a notable increase in oxygen during the event supporting the oxidation hypothesis. Global sea level fall and evaporite formation suggest that seawater salinity increased dramatically along continental margins, which may provide an alternative osmotic kill mechanism for the softbodied Ediacaran biota. Support for the salinity hypothesis comes from profound ẟ7Li and ẟ34S compositions of carbonate and pyrite, respectively, which arguably resulted from the distillation of lithium and sulfate from seawater into evaporite-rich lithologies.Item Integrated Geochemical Studies of the Shuram Excursion in Siberia and South China(2024) Pedersen, Matthew; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Ediacaran Period Shuram Excursion (SE) is a globally-distributed and highly controversial phenomenon where over millions of years, sedimentary carbonates record δ13C values of -10‰ and lower. This carbon cycle anomaly may reflect disequilibrium in the world’s oceans, driven by the oxidation of a large pool of dissolved organic carbon (DOC), with the oxidants sourced from the intense weathering of the continents, forcing major changes to ocean chemistry through the ventilation of the deep ocean, evidenced by a positive shift in carbonate uranium isotope values, and invoking the onset of early animal biomineralization. This study utilizes high-resolution carbonate Li isotopes from two SE-successions, U isotopes, REE abundances and Ce anomalies which reveal the dynamic interplay between intensified continental weathering associated with tectonic reconfiguration and the subsequent environmental and ecological response that may have been amplified by the ecosystem-engineering abilities of a newly discovered sponge-grade animal.Item Characterizing Chemical Signatures of Life via Mass Spectrometry(2023) Ni, Ziqin; Arevalo Jr., Ricardo; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The search for signs of life beyond Earth has been fueled by a natural curiosity about whether we are alone in the universe. Organic molecules, as the primary chemical components of terrestrial living organisms, are major targets in life detection missions. However, organic compounds have also been found in abundance in meteorites. They can be synthesized via abiotic processes such as lightning strikes, and naturally degraded with time. Searching for chemical signatures of life requires analog experiments to constrain chances of false positive detection and advancement of instrumentation to reduce possibilities of false negative measurements. The capacity to synthesize organics via abiotic mechanisms is influenced strongly by the redox condition. In this dissertation, the redox state of early Earth is estimated using trace element systematics in zircon grains. The Earth's surface is found to have reached a habitable redox condition as early as 4 billion years ago, coinciding with a time when Earth was still routinely bombarded by meteorites. Simulations of such high-speed impacts using high-power laser beams demonstrate the feasibility of synthesizing simple organic compounds from carbonates and nitrogen salts. Laboratory experiments and numerical modeling suggest that crater-forming impacts could have synthesized a considerable concentration of organics on the surface of Earth, Mars, and Ceres. The detection and characterization of organic molecules requires sophisticated analytical instrumentation. Laser desorption mass spectrometry (LDMS) and OrbitrapTM mass analysis are examples of next-generation techniques under development for conducting comprehensive chemical investigations in space. Although a combination of these two techniques enables the determination of the atomic composition of organic molecules, even complex polymers such as peptides, such an approach fails to recognize the 3D structure and sequencing of polymers. To facilitate the ionization and sequencing capability of peptides via LDMS, silicon nanoparticles are incorporated in the substrate as an alternative to conventional organic matrices but with reduced risk of forward contamination. The simultaneous measurement of mass to charge ratio and collision cross-section via Orbitrap mass analysis allows for rapid separation of organic molecules by their class, structure, and composition in sample mixtures. The techniques developed here are valuable for astrobiological exploration beyond Earth.Item No change in ENSO hydroclimate variability after the industrial revolution as recorded in ?18O of Tectona grandis L.F. from Southeast Sulawesi, Indonesia(2023) Herho, Sandy Hardian Susanto; Evans, Michael MNE; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)El Niño-Southern Oscillation (ENSO) is a quasi-periodic interannual oscillation of the ocean-atmosphere system in the tropical Pacific which greatly influences global climate variability. However, the long-term response to greenhouse gas forcing is still controversial. In this study, we measured the oxygen isotopic composition of ?-cellulose samples at intraannual resolution from independently crossdated teak cores (Tectona grandis L. f.) collected at Muna, Indonesia (5.3ºS, 123ºE, elev. 10m). The site and observation has been previously shown to provide an indirect measure of ENSO activity via local precipitation amount variations associated with ENSO. We created an ensembled composite of the interannual variability for the period 1680-2005 (316 years) using empirical high pass filtering and random sampling of intra-annual resolution measurements. In processing this time series composite, we used Singular Spectrum Analysis (SSA) to high pass filter the data for the interannual variability associated with ENSO. The annually-resolved composite time series of ?18O that we constructed has a higher resolution than other studies that have been conducted to reconstruct ENSO-hydroclimate activities in the western tropical Pacific region over this period. Using this ?18O composite, we compared the distribution of events in the period before and after the industrial revolution using the two-sample Kolmogorov-Smirnov(KS) test. We found no statistically significant change in the distribution of ?18O anomalies. The same statistical test was applied to the Niño 3.4 reconstruction from the Last Millennium Reanalysis (LMR). The results of this study suggest that if there is indeed a forced response of ENSO, it is as yet indetectable. This may be because the forcing is not yet large enough or the forced response is small relative to the unforced variability. Additional factors that might explain this result in the ?18O composite include its observational and interpretational uncertainty, and in the LMR reconstruction, the scarcity of tropical observational constraints and systematic error in the representation of ENSO in climate simulations.Item GENETICS, AGES, AND CHEMICAL COMPOSITIONS OF THE GROUP IIIE IRON METEORITES AND THE IRON METEORITE LIEKSA(2022) Chiappe, Emily; Walker, Richard; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Siderophile element concentrations, genetic isotopic data, and chronological data for ten group IIIE iron meteorites and the recently found iron meteorite Lieksa were determined. The modeling of siderophile element abundances shows that the IIIE irons can be related to one another through a common fractional crystallization process. Highly siderophile element data, however, indicate that the anomalous IIIE iron meteorite Aletai does not sample the same crystallization sequence as the bona fide IIIE irons. The bulk chemical characteristics of Lieksa are distinct from that of the established iron meteorite groups, indicating that, if it is an iron meteorite, it should be classified as an ungrouped iron meteorite. Isotopic data shows that, while the IIIE iron meteorites, Lieksa, and Aletai exhibit different HSE abundances, they exhibit similar genetic characteristics, indicating that they likely originated from the same nebular reservoir. Additionally, isotopic data indicate that all irons analyzed here sample parent bodies that differentiated within the first ~2 Myr of solar system history, which is consistent with other NC-type bodies.Item Deciphering Core Records of Carbon and Nitrogen in Typha-Dominated Freshwater Wetlands(2022) Ravi, Rumya; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I conducted decomposition experiments and examined soil characteristics in restored and natural freshwater marsh platform sites to decipher core records of soil C and N. Carbon loss rates and changes in ẟ13C and ẟ15N were obtained from decomposition experiments. Core samples at each site were analyzed for bulk density, weight %C, %N, ẟ13C, and ẟ15N. Typha C loss rates were similar among sites, and there was little change in ẟ13C composition, suggesting that DOC leaching is significant. Core carbon storage is higher in natural wetland sites. Initial Typha %N and ẟ15N reflect local N concentrations and sources to each wetland. ẟ15N increases between decomposed vegetation and upper cores in the tidal wetlands, possibly indicating denitrification. In N-rich wetlands, core %N and ẟ15N reflect differences in N sources and changes in N sources over time. In a wetland limited by N transport, core %N and ẟ15N may reflect vegetation N uptake.Item Earth's Radiogenic Heat Production and the Composition of the Deep Continental Crust(2022) Sammon, Laura Grace; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Much of the continental crust, the 40+ km thick plates of rock that make up the outer shell of our planet, is inaccessible to us living on its surface. Thus its composition is a mystery. We lack the technology to sample it directly at depths past 5 km, aside from a few deep (expensive) drill holes, so we must come up with a clever alternative for establishing its composition. The deep crust, the lower two-thirds of the continent, serves as a supporting root. When continents collide, they make mountain ranges, or when pulled apart they make rift valleys and basins. The composition of the deep crust, and specifically its silica, molecular water, and heat producing element (HPE: K, Th, U) contents, directly influence the crust's rheology during tectonic events and its potential for deadly earthquakes. Its chemical makeup is the sum of 4.5 billion years of crustal evolutionary processes that continuously shape and reshape the platform upon which society sits. An accurate description of the deep crust, however, requires careful integration of many different data sources. My research combines geochemistry with thermodynamics, geophysics, mineral-physics, seismology, and even particle physics to produce self-consistent models for the crust’s composition. Using thermodynamic calculations, I generate densities and seismic sound wave speeds from a range of chemical compositions. Matching these forecasted models to Earth’s seismic and gravity data allows me to translate the deep crust's physical properties into chemical compositions on both the regional and the global scale. Importantly, by quantifying not only the compositions, but also the uncertainties and the misfit in these results, I can better define the differences between competing models for crust deformation and evolution. Charting the distribution of Earth's geochemical resources has led to our collaborations with particle physicists, who need our expertise to determine the frequency of radioactive decay and therefore the amount of HPE decay emissions (known as geoneutrinos) in the crust; this geoneutrino flux is the background signal in their nuclear physics experiments. Their global flux measurements constrain our models for heat production and the amount of radiogenic energy that heats the Earth – which provides power to mantle convection, plate tectonics, and the destruction and creation of more continental crust.Our main sources of data are threefold. First, we have critically compiled geochemical analyses of >10,000 rock samples from pre-existing literature (Earthchem.org and affiliates). Second, we use geophysical data provided by sources such as the United States Geological Survey, the Earthscope USArray, and others to determine which of our geochemical samples could produce Earth’s observed seismic and density signals. Third, we partner with particle physicists in the United States, Canada, Italy, Japan, and China to jointly interpret data from three international geoneutrino detectors. By focusing on Earth as a whole system we seek a comprehensive understanding of its natural hazards and resources. Using multidisciplinary constraints, my goal is to build compositional models of the continental crust, with quantifiable uncertainties, that can be applied regionally and at larger scales. These findings will provide predictive insights on the strength and response of the continents when subjected to the dynamic processes of plate tectonics.Item A prototype miniature mass spectrometer for in situ analysis of trace elements on planetary surfaces(2021) Farcy, Benjamin Jacob; Arevalo, Ricardo D; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Interrogation of the chemical composition of rocky planets provides a deeper understanding of the history and evolution of the solar system. While laboratory studies of returned samples and remote sensing surveys of planetary surfaces can give insight into planetary history, one technique that has delivered major insights to planetary geology is in situ measurements of a planetary surface via mass spectrometry. Here, a new approach to spaceflight mass spectrometry is discussed, including an overview of the pursued scientific questions, the analytes targeted, and the prototype hardware in development. This effort constitutes the scientific and technological foundation of a landed planetary mission. This dissertation focuses on the history and evolution of the Earth-Moon system as recorded by trace elements. Specifically, the abundance and distribution of the heat producing elements (HPEs: K, Th, U) and their implications for mantle dynamics is considered. The radiogenic heat produced from K, Th, and U drives mantle convection, volcanism, and planetary dynamos. To understand better the chemical dynamics of radiogenic heat distribution in the Earth, the HPE abundance of a series of oceanic basalts was statistically analyzed. This analysis revealed the K/U ratio of the mantle and how it changes due to the enrichment or depletion of incompatible elements. The HPE abundance of the lunar interior was also discussed as a target of a future investigation, along with a series of trace element proxies meant to probe the lunar farside mantle. Further, an analysis of lunar farside craters provides a series of landing sites for an in situ mission, specifically for their surficial exposure of upper mantle material and later emplacement of lunar basalts. To access the trace element systems discussed in this dissertation, a prototype miniature inductively coupled plasma mass spectrometer (ICPMS) was developed to analyze trace elements in situ for landed planetary missions. First, the capability of the plasma to atomize and ionize input material was investigated. A plasma operating at reduced pressure can achieve 99\% ionization efficiency of most elements on the periodic table, with as much as a 50 to 100 times reduction in gas load and forward power compared to commercial systems for both He and Ar based plasma ion sources. The plasma system was integrated with a quadrupole mass spectrometer via a series of DC ion optics and vacuum housing, with its ion current and peak resolution optimized. Quantative data for an analyte spectrum of Kr demonstrates the ability for this instrument to resolve individual mass peaks, which lead to an accuracy and precision measurement of isotope ratios. This effort represents an end-to-end prototype miniature ICPMS, successfully demonstrating a viable instrument for landed planetary missions.Item Rb-Sr Radiometric Dating of Rocky Planetary Bodies via LA-ICPMS(2021) Almas, Kiran; Arevalo, Ricardo; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Constraining ages of surface features on rocky objects in the Solar System provides fundamental insights about the flux of impactors through time (including the putative Late Heavy Bombardment), rates of tectonic and volcanic processes, and temporal context for detected organic compounds. Spaceflight instrumentation is being developed to characterize these ages in situ. An LA-ICPMS is suggested as a candidate for a planetary chronology mission, with Mars as a case study; the capability of the technique to measure Rb and Sr isotopic signatures in geological samples with adequate accuracy within the 200 Myr (2σ) precision benchmark presented in NASA’s Technology Roadmap is tested. Data are presented that reports on these metrics for 87Sr/86Sr ratios, and a Monte Carlo simulation models synthetic isochrons to evaluate the accuracy and precision limitations of this method. A minimum of 10 data points per sample is suggested to meet the NASA benchmark.Item CHARACTERIZING THE DURATION, PERIODICITY AND CHEMICAL IMPACT OF FLUID TRANSPORT IN THE SUBDUCTING SLAB: INSIGHTS FROM ISOTOPE GEOCHEMISTRY OF HIGH-PRESSURE METAMORPHOSED OCEANIC CRUST(2021) Hoover, William Floyd; Penniston-Dorland, Sarah C; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Subduction zones are key loci of geochemical cycling and natural hazards on Earth including large earthquakes and explosive volcanic eruptions. Fluids produced during subduction are thought to play a role in all these processes, however, many aspects of fluid transport in subduction zones remain enigmatic. In this dissertation, three types of fluid-related features are examined: 1) an eclogite-facies vein and 2) an eclogite- facies shear zone block and metasomatic rind, both from the Monviso Ophiolite (Western Alps), and 3) two amphibolite-facies mélange blocks and rinds from the Catalina Schist (CA). The mechanisms, episodicity and duration of fluid transport associated with these fluid pathways are investigated with bulk and in situ Li isotope geochemistry, in situ Sr isotope and trace element geochemistry, and quantitative transport modeling. In the eclogite-facies vein, evidence for five distinct locally-derived fluid compositions suggests a complex process of fluid-rock interaction. The unusual geometry of alteration features in the host rock suggests that initial host rock heterogeneity led to the development of reactive porosity channels. A method for in situ measurement of Li isotopes in garnet by secondary ion mass spectrometry is developed to explore the relative chronology of fluid rock interaction preserved in mineral zoning. The equivalence of natural garnet and garnet-like glass reference materials is demonstrated and a correction procedure for instrumental mass fractionation due to MnO and FeO is proposed. The resulting method is highly adaptable and attains 2-4‰ precision at the 20-μm-scale. Application of this method to garnet from the eclogite-facies shear zone block and rind reveals negative ?7Li excursions to values as low as -9‰ that record fluid-driven Li diffusion and rapid garnet growth. Multiple negative excursions within a single garnet require at least four episodes of fluid infiltration in the shear zone. Lastly, the first fluid transport durations for the subduction interface are obtained by inverting Li isotopes profiles from the amphibolite-facies mélange blocks and rinds using an advection-diffusion model. Uniform durations of ~60 years for metasedimentary rock-derived fluid flow near peak metamorphic conditions suggest fluid infiltration was pervasive and episodic, with earlier episodes erased by the expansion of rinds into blocks.