A geochemical evaluation of depositional controls and paleoenvironmental reconstructions in organic-rich sedimentary deposits: Evidence from the modern Cariaco Basin, Venezuela, and application to the Devonian Appalachian Basin (New York)

Organic rich sedimentary deposits represent a quantitatively significant sink in the global biogeochemical cycle of carbon. Many processes and conditions have been identified that can contribute to the deposition, degradation, and preservation of such deposits, however, the relative importance of these factors is not well constrained. A more detailed understanding of the factors governing organic carbon deposition, and how variations in those factors can affect carbon cycling, is required in order to either make interpretations of paleoenvironmental conditions from the sedimentary record or make predictions of how current trends in Earth's climate system may ultimately affect the global environment. I have undertaken geochemical studies in the water column and sediments of the Cariaco Basin, Venezuela, and in the Devonian Oatka Creek Formation in order to identify inter-relationships between the processes and environmental conditions that affect production, alteration, and preservation of organic matter.; Molecular and isotopic results from the Cariaco Basin indicate that the intensity of primary productivity, the structure of the planktonic community in the overlying water column, and the fundamental controls on the carbon and nitrogen isotopic composition of organic matter varied as a result of climatic induced changes in oceanographic and biological conditions over the past 12 kyrs. The identification of these changes suggests that carbon cycling may be affected through alterations in the processes governing the sequestration of organic matter in sediments of low latitude environments.; An examination of diagenetic sulfurization processes in the Cariaco Basin sediments suggests that both pyrite and organic matter form continuously with depth, and that the sulfur for both processes is likely derived from pore water sulfide. The formation of significant amounts of organic sulfur during early diagenesis may have implications for reconstructing past atmospheric CO2 and O2 levels through feedbacks in the biogeochemical cycles of C, S, and O.; The results from the study of the Oatka Creek Formation suggest that a process of basin eutrophication due to seasonal (or longer) regeneration of nutrients from decomposing OM was initiated by extreme sediment starvation which resulted from a rapid rise in relative sea level.