This study will develop the Re-Os and U-Pb systems as organic- rich sediment geochronometers. Enrichment of these elements in organic-rich sediments during early diagenesis effectively set these radiometric clocks soon after deposition. Preliminary results demonstrate that these decay schemes can be successfully employed to obtain independent and concordant age determinations for the New Albany Shale, a Mississippian-Devonian boundary black shale from the Illinois Basin. The proposed research will extend the Re-Os system to dating both Cretaceous sediments and Proterozoic carbonaceous shales. By applying the Re-Os system to dating black shales and associated shelf carbonates at the Cenomanian-Turonian Boundary, we will examine potential variations in initial Os isotopic composition and determine whether the Re-Os system can yield high precision ages for young sediments. Our investigation of Proterozoic sediments from the Belt basin in the western U.S. focuses on demonstrating the utility of coupled studies using the U-Pb, Pb-Pb and Re-Os systems to date Precambrian sediments. Sampling across the east-west gradient in metamorphic grade within the Belt basin will enable us to evaluate the robustness of these chronometers under a variety of conditions.
