UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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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 A Molecular and Isotopic Approach to Examine the Role of Terrestrial Organic Matter in the Carbon Cycle of the Arctic Ocean(2008) Belicka, Laura Lee; Harvey, H. Rodger; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The organic carbon cycle in the Arctic Ocean is complicated by the delivery and redistribution of terrigenous material through rivers, sea-ice, and erosion. This dissertation combines an isotopic and molecular biomarker approach to assess the role that terrestrial organic carbon plays in the Arctic organic carbon cycle, with a focus on a comparison of geochemical proxies for the quantification of organic matter, an analysis of the sources and transformation of organic carbon to particulate organic matter (POM) and sediments, and an experimental investigation on the kinetics of recycling. Estimates for preserved terrestrial organic components varied considerably for identical sediment samples, suggesting that proxies account for different sources of terrestrial material (i.e., soil versus vascular plants). In spite of the variability, an estimated 12-43% of the organic carbon preserved in surface sediments was terrestrial in origin. This contrasted sharply with surface and halocline POM, in which marine inputs dominated despite spatial variability. With depth, POC composition reflected the increasing significance of inputs from secondary production and microbial degradation, as well as continental material. Acid-volatile sulfide (AVS) and redox-sensitive elements coupled with δ13C and lipid biomarkers demonstrated a transition from intense metabolism of labile marine organic matter in shelf sediments to slower sedimentary metabolism from occasional delivery of labile organic matter in the basin. Experimental determinations of the kinetics of microbial recycling revealed striking contrasts in marine and terrestrial organic carbon lability. Marine organic matter was recycled on very short timescales compared to terrestrial organic matter, corresponding to results of sedimentary and particle analyses. A simplified box model of organic carbon cycling in the Chukchi/Alaskan Beaufort Sea region reveals that 0.9 Mt and 0.7 Mt of marine and terrestrial organic matter, respectively, are buried in shelf sediments, while an additional 0.2 Mt marine and 0.1 Mt of terrestrial organic carbon are buried in basin sediments annually, confirming that land-derived organic matter plays a large role in carbon dynamics in Arctic systems, even on non-river dominated margins.