Paper No. 25-5
Presentation Time: 9:05 AM
CARBON CYCLE PERTURBATIONS AT THE FRASNIAN-FAMENNIAN BOUNDARY IN THE ILLINOIS BASIN, USA
The first large pulse of the Late Devonian mass extinction occurred at the Frasnian-Famennian boundary (the Kellwasser Event; ~372 Ma) and is characterized by drastic changes in atmospheric and oceanic conditions, leading to a loss of approximately 70-82% of species on Earth. Despite broad consensus that a major paleoenvironmental event occurred across this interval, the exact nature of this perturbation remains unknown, in part because the event was complex and occurred at both local and global scales. Building a complete picture of the Kellwasser Event requires investigation of sedimentary facies and geochemical trends at local, regional, and global scales, and in this study, we examine the record of the Kellwasser extinction within the Illinois Basin, USA. Particularly, we aim to test whether there was a carbon cycle perturbation associated with Kellwasser Event in the Illinois Basin, and what its potential origin may be. Positive δ13C isotope excursions in both carbonate and organic matter are seen in many strata worldwide across the Late Devonian extinctions, potentially associated with an increase in organic matter burial in anoxic oceans. These excursions have only sparsely been identified in North American black shales, however, and identifying their presence or absence in individual basins may allow for insight into the global extent of carbon cycle perturbation across the extinction horizons. In this study, organic carbon isotopes from 40 samples of the Storey core drilled in the southwestern depocenter of the Illinois Basin will be examined. The core is housed at the Illinois Geological Survey and covers the Upper Devonian Selmier and Grassy Creek members of the New Albany Shale. The Kellwasser Event is contained within these strata, and in this study, we hypothesize that a major positive δ13C excursion will be preserved in organic matter across the Kellwasser interval. Ultimately, the goal of this study is to determine whether there was a perturbation to the carbon cycle in the Illinois Basin across the Kellwasser Event, with future study aimed at extending the organic carbon isotope record to other Upper Devonian black shales from North American epeiric seas.