GEOCHRONOLOGY AND EXTINCTION IN THE FRASNIAN/FAMENNIAN BOUNDARY INTERVAL (LATE DEVONIAN) IN SHALLOW-MARINE PALEOENVIRONMENTS OF NEW YORK

In the Appalachian Basin, the Upper Devonian is represented by a thick package of siliciclastic sediments (the “Catskill Delta”), but diversity dynamics, including the Frasnian-Famennian (F/F) extinction, have not been studied in great detail. Here, we discuss both the placement of the F/F boundary and the dynamics of the extinction in shallow marine paleoenvironments in New York. In basinal facies of New York, the F/F boundary was placed just below the contact between the Hanover Shale (Java Formation) and the overlying Dunkirk Shale using conodont biostratigraphy (Over 1997, GSA Spec. Pap. 321). Presumably, in more onshore paleoenvironments, the boundary should be placed near the contact between the Wiscoy sandstone (the onshore temporal equivalent of the Hanover Shale) and the Dunkirk Shale. However, new work in the vicinity of Hornell, NY suggests that boundary should be placed higher. Conodonts suggest that the mapped Wiscoy-Dunkirk contact is Frasnian in age, and a subset of Frasnian brachiopod taxa (e.g., Spinatrypa sp.) extend above this contact. Spinatrypa has been found as high as the Canaseraga Sandstone, the next major sandy interval above the Wiscoy, raising the possibility that the boundary extends significantly above its previously presumed position in this area. Ongoing geochemical analyses should help resolve the exact position of the boundary. Current fossil collections suggest that extinctions in the F/F boundary interval were not simultaneous in New York; the last occurrences of brachiopod species are spread out over multiple transgressive-regressive cycles.