AN EXPANDED δ13CORG RECORD THROUGH THE LOWER KELLWASSER EVENT (LATE DEVONIAN) IN THE “CATSKILL DELTA” OF NEW YORK

Two pulses of extinction, the Lower and Upper Kellwasser events (LKW and UKW), have been recognized in the late Frasnian (Late Devonian). These events coincide with a global positive carbon isotope excursion and widespread deposition of organic-rich sediments in most studied sections. Carbon isotope data from sites across the globe indicate that these extinction events are related to a perturbation of the global carbon cycle and provide insight into the probable drivers of the extinctions. We developed a high-resolution δ¹³C_org record through a 95 m-long section near Cameron, New York, to constrain the timing of extinctions relative to regional and global carbon cycle perturbations and changes in depositional facies. The sediments that comprise the study area were deposited in the Appalachian foreland basin as part of the siliciclastic “Catskill Delta” complex. Our data show a ~4‰ positive excursion (from roughly -27 to -23‰) in the δ¹³C_org values associated with deposition of a dark shale interval. This interval has traditionally been correlated with the Dunkirk Shale of western New York State, but the coincident onset of dark shale deposition with the excursion, as well as independent biostratigraphic evidence (numerous brachiopods and all rugose corals go extinct at or near the base of this unit), indicate that this shale is the LKW-equivalent Pipe Creek Formation and not the Dunkirk. We observe significant variability in δ¹³C_org before and after the LKW indicating large-scale variability within the basin in the carbon cycle prior and subsequent to the extinction event. Potential drivers of these fluctuations include water depth/facies changes as a result of regional and/or eustatic changes in sea level, environmental perturbations that alter the rate of productivity and/or the weathering rate of organic material, or other factors.