Discerning Mechanisms of Environmental and Climatic Changes Associated with the Late Silurian (Ludfordian) Extinction Event

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The Silurian (419 to 443 million years ago) was an environmentally and biologically volatile interval of Earth history, which was characterized by numerous mass extinction events that are linked to reoccurring oceanographic changes. The goal of this funded project is to determine the mechanisms responsible for oceanographic and environmental changes associated with the most severe mass extinction in the Silurian. This project will utilize both newly developed and well-established geochemical approaches to develop a detailed history of oxygen levels in the oceans during this time interval. It is important to understand the history of oxygen concentrations in ancient oceans because changes in oxygen levels impact marine life, critical biogeochemical processes in the oceans and atmosphere, and the formation and preservation of economic hydrocarbon and mineral deposits. The project will provide meaningful hands-on field and laboratory experiences for undergraduate and graduate students, support the training of underrepresented groups in the geosciences, and support a high school science teacher to conduct cutting-edge research, which will provide motivation for new activities in their own classrooms. The project will address three research objectives: construct high-resolution isotopic analyses of sulfur and carbon, along with a suite of redox proxies (Fe-speciation, trace metal concentrations, thallium isotopes, I/Ca ratios), and detailed sedimentary facies analyses through late Silurian strata from multiple ocean basins on three separate paleocontinents. This will allow the research team to directly test existing hypotheses related to the causes of this late Silurian mass extinction event and associated large positive 13C excursion. Second, new high-resolution sedimentary geochemical data will be integrated with known paleobiological records via numerical stratigraphic methods (CONOP) for constraining possible causative connections between carbon cycle perturbation, marine extinction event, and eustatic sea-level records. Third, geochemical modeling will be used to further evaluate hypotheses regarding the links of local environmental changes, biotic extinction and recovery, and fluctuating global redox conditions in the oceans during the late Silurian.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.