A HIGH RESOLUTION STUDY OF NUTRIENT AND REDOX CYCLING IN THE KOPE FORMATION OF THE LATE ORDOVICIAN

The Ordovician (485-444 Mya) was a period of geologic, evolutionary, and climatic change during which there was an increased amount of tectonic activity, including the closing of the Iapetus Ocean and the Taconic Orogeny. The Great Ordovician Biodiversification Event (GOBE) caused a rapid increase in diversity and dramatic changes in paleoecology as new fauna quickly replaced Cambrian fauna. The Ordovician ended with the Hirnantian Glaciation, causing major climatic and environmental changes that is thought to have caused the first major mass extinction of the Paleozoic resulting in the loss of 60-70% of marine species. Though several studies that document long time-scale changes in geochemistry exist, there is currently a lack of high resolution geochemical data that can elicit different interpretations concerning the Ordovician biosphere. The Kope formation within the upper Ordovician contains a series of interbedded mudstone and fossiliferous limestone beds deposited within a shallow epeiric sea. It is an ideal location to study due to its well-established C-isotope, lithology, and biostratigraphy records. C-isotope excursions from the Ordovician are well studied and have been correlated across global regions. Lithology and biostratigraphy are also well studied across the local area; individual beds and fossil events have been traced throughout Indiana, Ohio, and Kentucky. A well-studied area such as the Kope formation allows for a controlled environment to study smaller scale nutrient cycles. Preliminary N-isotope analysis of a high-resolution section of the Kope formation shows what appears to be an overall positive excursion as well as smaller scale cycles based on lithology. It is possible broader scale studies overlook these small time-step cycles. Moreover, the mudstone and limestones present in the Kope are indicative of shallow marine facies, but existing C-isotope records are based on deeper marine facies. These records may not necessarily reflect the biogeochemical variability occurring in the shallow-water environment of the Kope. In this study, high resolution bulk N-isotopes and redox proxies will be used on a core section above and below existing N-isotope data to determine nutrient and redox cycles not previously recorded for this basin leading into the end Ordovician mass extinction.