Finney 9628343 An exceptional Upper Ordovician-Lower Silurian stratigraphic section was recently discovered in outcrops of the Vinini Formation in the Roberts Mountains of Nevada. It is the only section known anywhere in the world where an investigation can be carried out that relates carbonate 13 changes to biotic extinctions and re-radiations to sea-level changes. In addition, the paleontological, sedimentological, and geochemical records of the deep-marine, lower slope to continental rise depositional facies of the Vinini Formation can be compared closely to those of a coeval stratigraphic succession at Copenhagen Canyon in the Monitor Range of Nevada that represents a much shallower, outer shelf to shelf margin depositional setting. This project marks the first time that very different Late Ordovician facies within the same depositional basin may be directly compared using extensive and diverse stratigraphic records. It provides the opportunity to address the question of whether or not fluctuations in biological productivity and potential changes in atmospheric pCO2 coincided with the beginning and end of the Late Ordovician glaciation interval. It is a remarkable opportunity for a diverse scientific team to explore fundamental relationships in global earth systems. Because the Vinini Creek section has a thick cover of scree, a trench will be excavaed through the section by bulldozer. Then a team of scientists and students will log, describe, study, and sample 100 meters of section bed by bed. Various co-P.I.s, consultants, and students will sample for graptolites, conodonts, organic-walled microfossils, lithologies, stable isotopes, and paleomagnetism. The Copenhagen Canyon section has excellent surface exposures, but is mush less fossiliferous. Parts of it have been well sampled for fossils, but the potential for additional discoveries will be pursued. In addition, the section will be thoroughly samples for stable isotope analysis. Results will allow for the direct correl ation of 13C excursions to the biostratigraphies of graptolites, conondonts, and organic-walled microfossils and to distinct sedimentological records of sea-level changes that represent the waxing and waning of Gondwanan glaciation. Precise determination of the temporal relationships of paleontological, sedimentological, and geochemical signals between the Vinini Creek and Copenhagen Canyon sections and to others worldwide should provide definitive insights on causal relationships between profound global climatic, oceanographic, and biotic perturbations during the Late Ordovician.
