MIDDLE AND EARLY(?) WISCONSIN GLACIATIONS IN NY STATE: A LONGER GLACIAL RECORD WITH LINKAGES TO HEINRICH EVENTS

Heinrich events H1 to H3 have been linked to well-known Late Wisconsin ice advances by many researchers. Heinrich event H4 at radiocarbon age 33-35 kyr (38-40 kyr calendar yrs) is less well associated with the poorly dated mid Wisconsin record in North America. The Genesee Valley of western New York State preserves a well-dated record of events in the interval between 41 and 33 kyr at shallow depths in a buried bedrock valley that has the same geomorphic form as the adjacent Finger Lakes. The middle of the exposure is an interstadial floodplain with ages between 39 and 41 kyr. These sediments rest on undated (early?) Wisconsin drift. Above the fluvial sequence two deformation tills (primary lacustrine origin) with 33 to 35 kyr rhythmite ages also contain inclusions of reworked, well-preserved bone, peat, and wood ranging from 35 to >48 kyr old. The younger ages are broadly conformable with the sparse record of isolated mid Wisconsin ages previously reported for New York and with the more complete record near Toronto, Canada. The style of superposed events has some similarities with deformation till exposures at the Lake Ontario shore. The preservation of a shallow mid Wisconsin record that survived the late Wisconsin advance into Pennsylvania within a deep, drift-filled bedrock valley contrasts markedly with the thick, undated late Wisconsin record interpreted from seismic records for the central Finger Lakes. The well-preserved Genesee Valley section provides clear documentation of a mid Wisconsin advance into western NY coincident with Heinrich event H4. This evidence suggests that the subsurface record of glacial events in NY is probably more complex than generally assumed, due to the relatively scarce occurrence of datable organic remains in limited multiple till exposures. However, the reworked organic inclusions in the deformation tills provide a clear warning of problems inherent in interpreting isolated ages from partially exposed sections.