CARBON AND SULFUR ISOTOPE RECORDS ACROSS THE CAMBRIAN SKULLROCKIAN EXTINCTION EVENT FROM LAWSON COVE, UTAH

The middle Cambrian to Early Ordovician saw a series of extinctions events that occurred between the Cambrian Explosion and the Great Ordovician Biodiversification Events. One extinction event, the Skullrockian Extinction, is one of the most under-studied of these extinctions. Understanding this extinction is crucial for reconstructing the dynamics of early marine ecosystems and identifying the environmental drivers of biodiversity turnover during this transitional period. Geochemical evidence from better-studied extinction events in the same interval, such as the end-Marjuman and the Stairsian extinction events, suggests that ocean deoxygenation and euxinia were key contributors to marine biodiversity turnover. To investigate these processes during the Skullrockian extinction, we will analyze carbon (δ¹³C) and sulfur (δ³⁴S_CAS) isotopes in marine carbonate samples from sedimentary succession located at Lawson Cove, Utah. These isotopic proxies are widely used to reconstruct ancient carbon and sulfur cycling, providing insights into marine redox conditions, carbon burial rates, and potentially sulfidic conditions. Our δ¹³C data from Lawson Cove reveal significant excursions in the carbon isotope record most notably the Hellnmaria Red Tops Boundary (HERB) negative carbon isotope excursion that has been previously documented at this site. Additionally, the carbon isotope record around the Skullrockian Extinction differs from the previously studied extinctions, which occur at the beginning of the positive carbon isotope excursions. Further, the HERB occurs stratigraphically well before the Skullrockian Extinction so the links between these two events remain unclear. The perturbations to the carbon cycle represented by the HERB other changes in the carbon isotope record are likely linked to environmental instability, but their underlying drivers are currently still elusive. With our δ³⁴S results we will test for evidence of enhanced sulfate reduction, pyrite burial, and euxinia that during this time interval. These isotopic analyses will help clarify the potential role of oceanic anoxia in the Skullrockian extinction, carbon cycle changes, and, more broadly, provide broader insights into the relationship between unstable marine environments and early Paleozoic extinction events.