Paper No. 4
Presentation Time: 4:25 PM
δ13CORG RECORDS IN LATE DEVONIAN (FRASNIAN-FAMENNIAN) STRATA OF THE APPALACHIAN BASIN
There were numerous extinction events during the Late Devonian, including the Lower and Upper Kellwasser Events (LKW and UKW) near the Frasnian-Famennian (F-F) boundary. In the eastern United States, the F-F boundary interval is represented by the Chattanooga Shale in Tennessee, the Foreknobs Formation in West Virginia, and the West Falls, Java, and Candaway Groups in New York. We have revised the correlation of these events in shallow marine paleoenvironments of New York and northern Pennsylvania; based on biostatrigraphic data the dark shale above the Wiscoy Formation correlates with the Pipe Creek Shale (LKW), not the Dunkirk Shale (~UKW). We measured δ13Corg at a high sampling density from stratigraphic sections in Cameron, New York (CAM) and Tioga, Pennsylvania (TGB). A positive δ13Corg excursion of ~4‰ (from ~-27‰ to ~-23‰) at the base of the dark shale in these sections supports these revised correlations. The excursion is preceded by variable δ13Corg values in the upper Wiscoy (mean value of ~-27‰). δ13Corg values return to near pre-excursion values of ~-26‰ in the muddy-silty strata overlying the Pipe Creek at CAM. This excursion is recognized globally and is generally interpreted to reflect enhanced organic carbon burial during a period of widespread anoxia/dysoxia, which lowered pCO2 and global temperature. The positive excursion is also present at the base of the Pipe Creek at TGB, but δ13Corg values are depleted and variable within the middle-upper Pipe Creek and overlying pebbly sandstone beds, coincident with evidence for erosion and reworking of sediments and fossils. The reworking, channelization, and high-energy sandstones may reflect a rapid base-level drop, potentially glacioeustatic. Numerous species of brachiopods and all rugose corals go extinct in this event (LKW) in our sections.