Geology
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Item Isotope and Organic Geochemistry of a Unique Proterozoic, Postglacial Succession: The Lapa Formation, Vazante Group, Brazil(2007-05-09) Brody, Kristina; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study is the second to investigate biological characteristics associated with Proterozoic glaciation via molecular fossils from organic matter preserved in shale. In the Vazante Group, Minas Gerais, Brazil, the Serra da Lapa Formation unconformably overlies a formation recently dated to ca. 1.13 Ga. Lithologic and isotopic data suggest the Lapa represents deposition immediately after either an early Neoproterozoic "snowball Earth" ice age or a possible regional, but still low-latitude, late Mesoproterozoic ice age. The relative abundances of biomarkers and other organic molecules show variations that match lithologic and isotopic changes observed in 40 meters of exploration drill core studied. Inconsistencies among biomarker abundances as well as differences between the organic matter of the Lapa Formation and that of the underlying formation hint at heterogeneity among and within formations. A more complete picture of the Vazante Group is warranted before characteristics of preserved organic matter can be interpreted in the context of depositional environments or postdepositional processes.Item A CHEMICAL AND ISOTOPIC COMPARISON OF TWO 1ST-ORDER AGRICULTURAL TRIBUTARIES, KENT COUNTY, MARYLAND(2005-05-27) Teerlink, Jennifer; Candela, Philip; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nitrate derived predominantly from agricultural fertilizers results in algal blooms and wide-spread anoxia in estuarine environments. Roughly half the nitrate delivered to the Chesapeake Bay is derived from groundwater (residence time up to 40 years). Two 1st-order tributaries in eastern Maryland were sampled on five dates. Over the study interval, average nitrate, alkalinity, and delta 13C were 207 µM, 212 µM, and -12.1, respectively, in the ditched tributary, and 106 µM, 451 µM, and -9.7, respectively, in the unaltered tributary. Ditching of the western tributary results in discharge of less anthropogenically-altered groundwater. Nitrate, calcium, and magnesium concentrations decrease and 13C abundance of DIC becomes enriched along the reach. The unaltered tributary is stagnant in the headwaters, resulting in consumption of dissolved oxygen and denitrification. Alkalinity correspondingly increases suggesting reduced carbon as the electron source for this microbial process. Alteration of 1st-order tributaries influences the processing and delivery of nutrients.