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Paper No. 49-2
Presentation Time: 1:30 PM-5:30 PM
TESTING THE IMPACT OF FOREST EVOLUTION ON THE ORGANIC MATTER COMPOSITION OF ILLINOIS BASIN DEVONIAN MARINE BLACK SHALE
The evolution of forests during the Middle to Late Devonian (about 375 million years ago) acted as a catalyst for a variety of changes to atmospheric composition and the Earth climate system. Previous studies have proposed a relationship between the newly evolving forest ecosystems and enhanced nutrient runoff to oceans with ocean anoxia, black shale deposition, global climate change, and biotic crises. To better understand this relationship, this study uses samples collected from core and outcrop in the Illinois Basin to assess terrestrial biomass input to marine settings through time, and the relationship of terrestrial and marine organic matter with changes in proximity to open ocean settings. Samples were collected from two locations in the Illinois Basin: an outcrop at Gallatin, Tennessee and a core from Lawrence County, Indiana. Organic carbon isotopic analysis is being used to differentiate marine from terrestrial organic matter. Additionally, x-ray fluorescence and loss-on-ignition techniques were used to provide a better understanding of the lithology of the samples, paleoredox conditions during deposition, and sedimentation rate/organic matter dilution. Preliminary results to date from the Blocher Member of the New Albany Shale at Gallatin, Tennessee suggests that there is cyclicity in organic carbon preservation in black shale lithologies which may correspond to siliciclastic influx represented by the proxy Ti/Al. In the core from Lawrence County, Indiana, cyclicity in the total organic carbon is not as evident and total organic carbon decreases through time through the Blocher Member. Additionally, handheld xrf data suggest elevated molybdenum values, indicating anoxic conditions. The data from this study will provide a better understanding of past geologic events and a natural baseline for predicting the future impacts of anthropogenic climate and environmental change, and resulting carbon cycle perturbations.