Northward subglacial drainage during the Mackinaw Interstade in the Cayuga basin, central New York, USA

The history of deglaciation in the Finger Lakes region since the Valley Heads readvance is questioned by recent research in the Cayuga basin, which concludes that, instead of forming a series of proglacial lakes, drainage during the Mackinaw Interstade was into the Laurentide ice sheet. First suspected in the Dryden–Virgil Valley where there is an absence of a lake outlet or surficial lacustrine deposits, this conclusion was explicitly revealed in the Sixmile–Willseyville trough where ice margin channels funneled water into the ice front. Further support was found in the Cayuga Inlet Valley, where a kettle kame terrane sloped northward into the ice front. Northward drainage was preceded by southerly drainage, with reversal occurring about 16.3 kyr ago. Multi-channel seismic profiles at the south end of Lake Cayuga reveal a south-sourced subaqueous sedimentary fan at the base of the lacustrine sequence. This fan is correlated with a coarse and heterogeneous clastic sequence penetrated in water wells in the City of Ithaca and requires northward drainage into a subglacial lake, which precludes the existence of proglacial lakes Ithaca, Newberry, and Hall. The proposed subglacial flow path is through the Cayuga trough, exiting the ice front eastward in the Mohawk Valley. Subglacial drainage from the Cayuga trough probably was part of a regional subglacial drainage system during the Mackinaw Interstade. Studies north of Lake Ontario have led to the proposal of a subglacial lake in the Ontario basin at that time, which likely also drained into the Mohawk Valley.