THE FRASNIAN-FAMENNIAN EXTINCTION IN NEW YORK AND PENNSYLVANIA: A MICROSTRATIGRAPHIC STUDY

Marine faunas in New York and Pennsylvania experienced several pulses of extinction in the late Frasnian (Late Devonian). Here we report on one of these pulses based on microstratigraphic (bed-by-bed) sampling of benthic fossils (primarily brachiopods) from four stratigraphic sections. These sections represent a depth gradient that spans approximately 80 km. This extinction pulse is coincident with the deposition of a black shale bed, the geochronology of which we are re-examining. Several ostensibly Frasnian taxa, including one conodont and a species of Spinatrypa, are found above this shale, suggesting that it might not mark the end of the Frasnian. The most notable victims of this pulse of extinction were the strophomenid brachiopods, although other groups of brachiopods experienced losses as well. Rugose corals also appear to suffer. Several typical Famennian taxa, such as “Athyris” angelica and “Thiemella” leonensis, first appear stratigraphically above this horizon. Possible extinction mechanisms are being evaluated in relation to the environmental preferences of survivors and victims.