SHALLOW MARINE NITROGEN CYCLING DURING THE FRASNIAN-FAMENNIAN MASS EXTINCTION IN THE APPALACHIAN BASIN

Mass extinctions are often associated with extreme changes in environmental conditions. Studies of the Late Devonian (Frasnian-Famennian) extinction event have implicated numerous potential kill mechanisms including widespread oceanic anoxia and global cooling. The Frasnian-Famennian extinction intervals (Lower and Upper Kellwasser events) are often associated with deposition of organic-rich sediments, low-oxygen conditions, and nitrogen cycle perturbations. In the Appalachian Basin, the Kellwasser-equivalent beds were deposited under alternating dysoxic/anoxic conditions. Previous studies of distal portions of the Appalachian Basin associate the Kellwasser events with weakly depleted ¹⁵N values (0 to -1‰), suggesting redox conditions and water column stratification controlled nitrogen cycling through this interval. However, there is a paucity of data from onshore localities. Major and trace element concentrations from the shallower portions of the basin are consistent with intermittent periods of water column dysoxia through the Kellwasser events, suggesting the potential for similar patterns in nitrogen cycling. Analysis of bulk sedimentary δ¹⁵N offers insight into the combined influence of water column redox conditions and paleoceanographic conditions on biogeochemical nutrient cycling. Here, we present data detailing δ¹⁵N, δ¹³C_org, and sedimentology from localities throughout the shallow portions of the Appalachian Basin in New York and Pennsylvania. Analysis of these data indicate increasingly positive shifts in δ¹⁵N values (+2.5-3‰) during the Lower Kellwasser event in the shallow Appalachian Basin are closely tied to redox conditions, reflective of increased denitrification of inundated terrestrially organic material in shallow suboxic conditions.