FRASNIAN (UPPER DEVONIAN) MARINE STRATA OF NEW YORK STATE

The Frasnian strata in New York State represent terrestrial to offshore marine environments that transition through the classic Upper Devonian magnafacies established by stratigraphers in the last century – Catskill – Chemung – Portage – Genesee. Refined conodont and sequence stratigraphy provides a better understanding of the offshore marine units and their lateral relationships. The base of the Frasnian, defined by the first occurrence of the conodont Ancyrodella rotundiloba “early form,” is within the upper Geneseo Shale – MN Zone 1 – in the lower part of the classic Genesee facies that follows the Taghanic event and major flooding of the Devonian II B flooding cycle of Johnson et al. (1985). The base of the middle Frasnian is close to the base of the Middlesex Shale, which marks the II C flooding and the base of the Sonyea Group. The base of the thick Rhinestreet Shale, which marks the base of the West Falls Group, is in MN Zone 6 or 7. The base of the upper Frasnian is near the top of the Rhinestreet, marked by the II D1 flooding and global semichatovae event which falls in MN Zone 11. The Java Group – upgraded from a formation within the West Falls Group - is marked by the base of the Pipe Creek Shale – representing the II D2 flooding which is at the base of MN Zone 13. This is a globally recognized unit correlative to the Lower Kellwasser Horizon. The base of the Famennian is within the upper Hanover Shale Formation and the more near-shore equivalent Wiscoy Formation. In the offshore facies the boundary is recognized by the first occurrence of the conodont Palmatolepis triangularis in the absence of diagnostic Frasnian taxa, which occurs at or near the top of a distinct black shale bed – the Upper Kellwasser Horizon equivalent; in the topmost Wiscoy Formation the extinction of Frasnian brachiopods and the first occurrence of Athyris angelica best approximate the boundary. The Dunkirk Shale at the base of the Canadaway Group, last of the thick Devonian black shales in New York, represents the II E1 flooding in the early Famennian.