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

Two mass extinction events known as the Ireviken and Mulde Events took place during the Wenlock Epoch of the Silurian Period that affected conodonts, graptolites, and trilobites. The extinction intervals are 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 and Mulde Extinction Events. These extinction events also coincide with major perturbations to the global carbon cycle and the onset of the Ireviken and Mulde positive carbon isotope excursions. 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 these intervals.

To investigate this, we sampled the Measley Ridge section in Southern Ohio for the onset of the Ireviken Excursion and a new core (Altajme) from Gotland, Sweden, for the Mulde Excursion at extremely high resolution to look for discrete isotopic events in the lead up to the onset of the positive carbon isotope excursions. In each locality we took nearly 400 samples from the onset of each excursion with a sample spacing of 3-5cm over 10+ meters of section. We found both excursions well displayed with carbon isotope values in excess of +5‰ for the Ireviken Excursion and +3‰ for the Mulde Excursion. In addition, we also found several discrete features in the isotope data prior to, and during, the onset of the Ireviken and Mulde Excursions 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 each locality to determine if the isotopic signals do, in fact, occur at the same stratigraphic levels as the extinction datums