INTEGRATED HIGH-RESOLUTION BIOCHEMOSTRATIGRAPHY OF THE SCHLAMER #1 DRILL CORE, SOUTHERN ILLINOIS, USA: MARINE REDOX CYCLING DURING THE IREVIKEN AND MULDE POSITIVE CARBON ISOTOPE EXCURSIONS

The Schlamer #1 Drill Core was recovered from Alexander County, Southwestern Illinois, and contains more than 250 feet of Silurian strata. Conodont and carbon isotope data demonstrate that the core spans an interval at least from the Hirnantian Stage through the Pridoli Series. At present more than 400 carbonate carbon isotope samples, 150 conodont samples, 1,200 pXRF data points, and 150 solution ICP-MS samples have already been completed and demonstrate that the core contains the Hirnantian, Ireviken, Mulde, and Lau positive carbon isotope δ¹³C_carb excursions and associated biogeochemical events.

As suggested by previous studies, significant increases in redox-sensitive elements occur at the onset of both the Ireviken and Mulde biogeochemical events that may have played important roles in the development of the ocean-atmosphere-biosphere system during the Wenlock Epoch. In particular, REE and redox-sensitive elemental abundance data from the Schlamer #1 Core show evidence of marine anoxia during the Ireviken and Mulde positive δ¹³C_carb excursions. These findings provide support for a marine anoxia cause for the positive carbon isotope excursions of the Wenlock Epoch as opposed to their being the result of either carbonate weathering or diagenetic processes.