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相沉积物建立晚石炭世的高分辨率同位素地层学。早期（Grossman et al., 1985; Adlis et al., 1987）对德克萨斯州中北部的弗吉尼亚（宾夕法尼亚晚期）旋回沉积物的研究表明，在许多海洋生物的钙质壳中保存了原始的同位素组成。这些材料的可用性为开发石炭纪晚期和二叠纪早期（1500万年至2000万年的时间间隔）的近乎连续的同位素记录提供了独特的机会。这样的记录，在适当的古生物学和沉积学控制下，可以用于1)记录海水18O的长期变化，2)顶部确定沉积时海底古温度和古深度的变化，3)利用古深度数据确定晚石炭世海平面上升变化的幅度。区分18O记录的古温度趋势和18O海水的变化一直阻碍着同位素研究。详细的古生物学和岩性数据将用于区分由局部盐度变化或与古深度变化相关的温度变化引起的同位素趋势与由与冰川作用相关的海水18O变化引起的同位素趋势。作为对深度效应的进一步检查，我们将根据零深度视界的厚壳腕足动物确定一个单独的同位素曲线。这种方法将允许量化产生石炭系旋回沉积物的海平面波动变化，但更重要的是，将产生同位素地层学，用于测试和扩展石炭系和二叠纪的新兴旋回地层学，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.