SEARCHING FOR GEOCHEMICAL SIGNATURES OF STEP-WISE EXTINCTION LEVELS DURING THE IREVIKEN (SILURIAN) EXTINCTION EVENT

A mass extinction event known as the Ireviken Event took place near the Llandovery/Wenlock boundary during the Silurian Period that affected conodonts, graptolites, and trilobites. The extinction interval is marked by a series of step-wise extinction datums that each left their own signature in the fossil record. Collectively, these closely spaced extinction levels comprise the Ireviken Extinction Event. This extinction event also coincides with a major perturbation to the global carbon cycle and the onset of the Ireviken positive carbon isotope excursion. What is currently unclear however, is if each of these extinction levels also left a distinct geochemical signature in the rock record and if they can be identified in the carbon isotopic record of this interval.

To investigate this, we sampled the Measley Ridge section in Southern Ohio at extremely high resolution to look for discrete isotopic events in the lead up to the onset of the Ireviken positive carbon isotope excursion. We took nearly 400 sample from the upper part of the Estill Formation and the lower part of the Bisher Formation with a sample spacing of 3-5cm over approximately 15 meters of section. We found the Ireviken Excursion well displayed with carbon isotope values in excess of +5‰. In addition, we also found several discrete features in the isotope data prior to, and during, the onset of the Ireviken Excursion that could be geochemical signatures of the extinction datums. This work is phase one, and the next step is to process the conodont samples collected from this outcrop to determine if the isotopic signals do, in fact, occur at the same stratigraphic levels as the extinction datums.