CHANGES IN PALEOECOLOGICAL GRADIENTS RESULTING FROM THE FRASNIAN-FAMENNIAN EXTINCTION EVENT (LATE DEVONIAN) IN THE APPALACHIAN FORELAND BASIN

The Frasnian-Famennian (F-F) extinction in the Late Devonian was one of Raup & Sepkoski’s “Big 5” mass extinctions of the Phanerozoic. It consisted of two pulses, the Lower and Upper Kellwasser extinction events (LKW and UKW), that were associated with carbon cycle disruption, global cooling, and ocean dysoxia/anoxia. The F-F impacted numerous marine clades, including brachiopods, ammonoids, rugose and tabulate corals, and stromatoporoids. Upper Devonian strata in present-day Pennsylvania and New York represent an onshore-offshore paleoenvironmental gradient stretching from southeast to northwest. Our work in this field area indicates that the LKW was more intense than the UKW for brachiopods, with atrypids and strophomenids affected most strongly. Here, we analyze changes in brachiopod species distributions along this onshore-offshore habitat transect that resulted from the LKW extinction and the immigration/origination of new species in its aftermath. We compared bulk samples from the Wiscoy Formation (pre-LKW) and Canaseraga Formation (post-LKW) from localities in New York and north-central Pennsylvania. We identified ~8000 brachiopod fossils from each formation and assessed variation in species composition among samples using non-metric multidimensional scaling (NMDS). Extinctions occurred across the habitat gradient during the LKW, and the extinct species (largely atrypids, strophomenids, as well as orthids) were largely replaced by productids. The taxonomic selectivity and broad environmental spread of the extinction, combined with the differential success of the productids in its aftermath, resulted in a dramatic faunal turnover. However, surviving species appear to have maintained their habitat preferences.