HIGH LEVEL ERIE INTERSTADE PROGLCIAL LAKES IN THE CENTRAL FINGER LAKES REGION, NY, AND THEIR IMPLICATIONS

Low lake levels in the Lake Erie basin suggest easterly drainage through the Mohawk Valley during the Erie Interstade. The coarse Little Falls Gravel of about the same age was suggested to be a result of this drainage. Both would require that the Ontario Lobe retreated into the Lake Ontario basin during the Erie Interstade. Support for retreat of this extent requires documentation of the behavior of the Ontario lobe in central New York during the Erie Interstade, which has been lacking. Four sites of proposed Erie age have recently been identified in the Cayuga watershed that bear on this problem. These sites are: 1) in the Inlet Valley where a thick proglacial lake sequence is traced from beneath the Valley Heads end moraine in well logs to exposures further north. Disseminated plant material in the upper part of this sequence is currently being dated. Surface and well data indicate that, north of these exposures, the Port Bruce glacial deposits plunge northward beneath younger proglacial lacustrine clays and the older lacustrine sequence, and has not been found in well records; 2) near Varna along Fall Creek where ice-proximal varves underlie Valley Heads deposits and overlie an older till. Varve analysis and paleomagnetic declination measurements show ~10cm/yr sedimentation rates and a paleo-declination of 357.2±0.7° (69 specimens, 4 horizons, AF demag 30 mT). This declination matches that of the lower Newport beds in the western Mohawk Valley that represent the beginning of ice recession leading to the Erie Interstade; 3) well data in Sixmile Valley south of Brooktondale record a lacustrine sequence beneath Valley Heads till that overlies probable Nissouri till. The lacustrine sequence does not extend much further NW, where only a single late Wisconsin till occurs, indicating either minimal ice recession to only south of Ithaca or glacial erosion of the Erie lacustrine package by during Valley Heads advance; and 4) along upper Sixmile Creek where lacustrine/fluvial sediments lie between Valley Heads and Nissouri tills and require a nearby ice blockage. Although there are still data gaps in the Erie Interstade record, the available information does not provide evidence of the retreat of ice to the northern Finger Lakes.