Sedimentary Geochronology: Coupled Studies of Re-Os and U-Pb

本研究将发展Re-Os和U-Pb系统作为富有机质沉积物地质时计。早期成岩作用中富有机质沉积物中这些元素的富集有效地在沉积后不久设置了这些辐射时钟。初步结果表明，这些衰减方案可以成功地用于新奥尔巴尼页岩的独立和一致的年龄测定，新奥尔巴尼页岩是伊利诺斯盆地的密西西比-泥盆系边界黑色页岩。该研究将把Re-Os系统扩展到白垩纪沉积物和元古宙碳质页岩定年。通过将Re-Os系统应用于塞诺曼—turonian边界的黑色页岩和相关陆架碳酸盐岩定年，我们将研究初始Os同位素组成的潜在变化，并确定Re-Os系统是否可以为年轻沉积物提供高精度年龄。我们对美国西部Belt盆地的元古代沉积物进行了研究，重点展示了使用U-Pb、Pb-Pb和Re-Os系统进行耦合研究的实用性，以确定前寒武纪沉积物的年代。在“带”盆地内横跨东西梯度的变质等级取样，将使我们能够评估这些计时器在各种条件下的稳健性。

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.