INVESTIGATING REDOX CONDITIONS AND MECHANISMS FOR THE END ORDOVICIAN (HIRNANTIAN) MASS EXTINCTION: A WESTERN LAURENTIA PERSPECTIVE

Many extinction events in the Phanerozoic have been associated with an expansion of marine anoxic or euxinic (anoxic and sulfidic) conditions as a possible kill mechanism. However, the Late Ordovician Mass Extinction (LOME), the first of the “Big 5” mass extinctions, until recently has not been associated with this particular kill mechanism. Dramatic changes in climate, sea surface temperatures, and sea level were the key mechanisms initially hypothesized as drivers for the LOME. However, recent paleoredox investigations (iron speciation and trace metals) from south China and Baltica have shown that anoxic/euxinic conditions played a role in the LOME. In this study, we use both global (δ³⁴S_CAS) and local (I/Ca) redox proxies to investigate an anoxic/euxinic mechanism for the LOME. To do so, we will analyze two well studied Late Ordovician successions from the carbonate dominated shelf-slope area of western Laurentia located within the Great Basin in central Nevada for δ¹³C_carb, δ³⁴S_CAS, and I/Ca ratios. Previously δ¹³C_carb has been used to determine changes in the carbon cycle as well as changes in weathering. With our new data, δ³⁴S_CAS will determine changes in global pyrite burial rates which is generally linked to extent of water column euxinia. Lastly, I/Ca ratios will be used as a local redox proxy to constrain oxygenation of the overlying water column. For the first time, this study will combine local ang global redox proxies to elucidate the spatiotemporal geochemical trends of marine oxygenation during the LOME. This data combined with the known temporal extinction record will provide us with potential ties to key mechanisms to explain the extinction patterns. With the data collected from this study, we hope to elucidate the key mechanisms that induced the second largest mass extinction in Earth’s history.