186Os Investigations into the Origins of Osmium in Seawater

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ABSTRACTOCE-0116955The ultimate source of Os into the modern ocean is only partially constrained. At issue is whether radiogenic Os is derived from average upper continental crust or whether Os is the result of weathering of organic-rich sedimentary rocks. For this reason, a PI from the University of Maryland will develop the 190Pt-186Os isotope system as a tracer of chemical input into the oceans by carrying out the following research: (1) constrain the 186Os/188Os of the modern ocean via analysis of young oceanic Mn-nodules and oxidized metalliferous sediments; (2) constrain the average 186Os/188Os of the continental crust via the analysis of loess and freshwater Mn-concretions from a variety of locations in the United States, Europe and Asia; and (3) constrain the average evolution of 186Os/188Os in organic-rich sediments via the analysis black shales from the Proterozoic Chelmsford/Onwatin and Virginia Formations, Cambrian shales from the Hunan Province in China and Devonian shales from the Yukon Territory of Canada. Once these analysis have been completed and if any analytically discernable differences are confirmed between the 186Os/188Os ratio of felsic crust and organic-rich sediments, then the PI also will determine the evolution of 186Os/188Os in Cenozoic seawater via analysis of metalliferous sediments of known age.