Isotopic Studies of Late Paleozoic Cyclical Sedimentary Deposits

该项目的目标是利用北美大陆中南部的海洋沉积物，建立晚石炭世的高分辨率同位素地层学。早期(Grossman等人，1985；Adlis等人，1987)对德克萨斯州中北部的Virgian(宾夕法尼亚晚期)旋回沉积的研究表明，原始同位素组成保存在许多海洋生物的钙质贝壳中。这种物质的可获得性提供了一个独特的机会，可以发展出最新的石炭纪和最早的二叠纪(间隔1,500-2,000万年)的几乎连续的同位素记录。在适当的古生物学和沉积学控制下，这种记录可以用来1)记录海水18O的长期变化，2)顶部确定沉积时海底的古温度和古深度的变化，以及3)利用古深度数据来确定晚石炭世海平面变化的幅度。区分海水18O记录的古温度趋势和18O的变化一直是同位素研究的障碍。将使用详细的古生物和岩性数据，以区分由局部盐度变化或与古深度变化有关的温度变化引起的同位素趋势，以及由与冰川有关的海水18O变化引起的同位素趋势。作为对深度效应的进一步检验，我们将从零深度层位确定一条单独的基于厚壳腕足类的同位素曲线。这种方法将能够量化产生石炭纪旋回沉积的海平面变化，但更重要的是，将产生一种同位素地层学，用于测试和扩展石炭纪和二叠纪的新出现的旋回地层学，最终导致全球同位素事件地层学。

The goal of this project is to establish a high resolution isotope stratigraphy for the late Carboniferous using marine deposits from the south-central portion of the North American continent. Earlier work (Grossman et al., 1985; Adlis et al., 1987) on Virgilian (late Pennsylvanian) cyclic deposits in north- central Texas has shown that original isotopic composition is preserved in many calcitic shells of marine organisms. The availability of such material provides a unique opportunity to develop a near-continuous isotopic record for the latest Carboniferous and earliest Permian (a 15-20 million year time interval). Such a record, with proper paleontologic and sedimentologic control, can be used 1) to document secular variation in the 18O of seawater, 2) top determine changes in paleotemperature and paleodepth of the sea floor at the time of deposition, and 3) using paleodepth data, to determine the magnitude of late Carboniferous eustatic changes in sea level. Distinguishing the 18O record paleotemperature trends from changes in the 18O of seawater has always hampered isotopic studies. Detailed paleontologic and lithologic data to distinguish isotopic trends caused by local salinity change, or temperature change associated with changes in paleodepth, from isotopic trends derived from changes in seawater 18O associated with glaciation will be used. As a further check on depth effects we will determine a separate isotopic curve based on thick-shelled brachiopods from the zero depth horizon. This methodology will permit quantification of the eustatic sea level changes that produce Carboniferous cyclic deposits, but more importantly, will produce an isotope stratigraphy for testing and extending the emerging cycle stratigraphy of the Carboniferous and Permian, eventually leading to a global isotopic event stratigraphy.