Isotopic Studies of Late Paleozoic Cyclical Sedimentary Deposits

研究目标是建立详细的、半连续的晚古生代同位素记录并检验其准确性；2)将同位素地层学应用于古环境分析，以确定晚古生代旋回沉积的成因。这两个目标是不可分割的，因为了解沉积环境对解释同位素记录至关重要。该研究采用了严格的措施，以避免取样成岩改变的物质。将腕足类动物壳从页岩基质中分离出来，包埋在环氧树脂中，并进行薄切片。在阴极发光和平面光下拍摄这些薄片的照片，并使用牙签从薄片中取样非发光方解石作为地图。利用电子探针对所选壳层进行元素分析，证实了利用阴极发光对改变壳层的鉴别。这项研究将集中在数量有限的腕足动物物种上，从而尽量减少或消除对同位素组成的生物影响。还将收集沉积学和古生物学数据，为古环境变化提供独立的证据。PIs将分析新墨西哥州、俄克拉荷马州、堪萨斯州和密苏里州宾夕法尼亚晚期沉积物中的腕足类动物，以检查同位素组成的横向变化：1)测试使用13C来关联地层的可能性；2)定义海洋古温度和化学的横向和时间梯度。PIs还将扩展德克萨斯州晚古生代同位素地层学，以研究德克萨斯州陆表海的古环境变化，并提供详细、准确的同位素地层学，为其他晚古生代化石稳定同位素研究提供标准。项目将应用创新技术来分析地球历史时期的全球环境变化，就像今天一样。在这个气候变化时期，对全球变化的分析可以揭示有关气候变化的原因、速度和后果的信息。

Research objectives are the development of a detailed and semi-continuous isotopic record for the late Paleozoic Era and the testing of its accuracy, and 2) the application of isotope stratigraphy to paleoenvironmental analysis with the specific goal of determining the origin of late Paleozoic cyclical sedimentary deposits. These two objectives are inseparable since understanding the depositional environment is vital for interpreting the isotopic record. The study employs stringent measures to avoid sampling diagenetically altered material. Brachiopod shells are separated from shale matrix, embedded in epoxy, and thin-sectioned. Photographs of these thin sections are taken under cathodoluminescence and plane light, and used as a map to sample non-luminescent calcite from the thin section with a dental pick. Electron microprobe elemental analysis of select shells is used to confirm the use of cathodoluminescence to identify altered shell. The study will concentrate on a limited number of brachiopod species, thereby minimizing or eliminating biological effects on isotopic composition. Sedimentological and paleontological data will also been collected, providing independent evidence for paleoenvironmental change. PIs will analyze brachiopods from late Pennsylvanian deposits in New Mexico, Oklahoma, Kansas and Missouri to examine lateral variations in isotopic composition 1) to test the possibility of using 13C to correlate strata and 2) to define lateral and temporal gradients in ocean paleotemperature and chemistry. PIs will also extend the isotope stratigraphy of the late Paleozoic in Texas to examine paleoenvironmental changes in the epicontinental seas of Texas and to provide a detailed and accurate isotope stratigraphy which can be used as the standard for other studies of stable isotopes in late Paleozoic fossils. Project will apply innovative techniques to analysis of global environmental change in a period of earth history much like today's. Analyses of global change in this time of climatic change may reveal information about the causes, rates and consequences of climate change.