101-5 Extinction and Recovery of Brachiopods during the Frasnian-Famennian (Late Devonian) Mass Extinction in the Appalachian Basin: Updated Results

Abstract:

The Late Devonian Mass Extinction was one of the most severe biodiversity crises of the Phanerozoic. It featured two major extinction pulses, the Lower and Upper Kellwasser events, both of which are associated with taxonomic turnover and positive carbon isotope excursions at sites around the world.

Shallow-marine Upper Devonian rocks of the Appalachian Basin of south-central New York and north-central Pennsylvania span the Frasnian-Famennian boundary interval, preserving both Kellwasser events. However, an understanding of these events has been hindered by difficulties correlating these strata with their deeper-water, distal expressions in western New York. Based on new evidence from conodont biostratigraphy (Over 2025, doi: 10.1130/abs/2025NE-407407), we discuss the correlation of the Frasnian-Famennian boundary interval, including the West Falls, Java, and Canadaway groups. In particular, a dark shale unit previously correlated with either the Lower Kellwasser Event or the lower Famennian Dunkirk Formation appears to be correlative with the Upper Kellwasser Event (uppermost Frasnian).

Within this stratigraphic context, brachiopod collections from the upper Frasnian and lower Famennian preliminarily suggest that about a third of species were lost during the Lower Kellwasser, and nearly half in the Upper Kellwasser. Species richness recovered completely after the Lower Kellwasser and partially after the Upper Kellwasser.

Additionally, our stratigraphic revisions suggest the presence of a third, more minor event in the early Famennian. It is associated with a gray siltstone bed in the Canaseraga Formation, as well as with a positive isotope excursion. The last atrypid species in the basin disappears at this event, leading previously to the suggestion that it might correspond with the Upper Kellwasser Event. It is unknown whether this was a local event, or whether it can be correlated with geochemical or faunal changes in other basins. Brachiopod faunas display a spatial reorganization along the onshore-offshore paleoenvironmental gradient across this horizon despite minimal taxonomic turnover. This “Canaseraga Event” may indicate continued biotic upheaval between the Frasnian-Famennian and Devonian-Carboniferous crises in the Appalachian Basin.

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