Isotopic Studies of Late Paleozoic Cyclical Sedimentary Deposits

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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.