Paper No. 4
Presentation Time: 9:05 AM
MIDDLE WISCONSIN CHERRYTREE STADE ICE ADVANCE ONTO THE APPLACHIAN PLATEAU IN CENTRAL NEW YORK COINCIDENT WITH HEINRICH EVENT H4
The Genesee Valley and Sixmile Creek, a tributary to the Cayuga Lake trough, contain detailed stratigraphic records of a middle Wisconsin ice advance that covered most of the central Finger Lakes region circa 34 to 36 14C kyr BP (38-40 kyr BP). These two well-documented records correlate reasonably well with Cherrytree Stade deposits, such as the Seminary and Meadowcliff diamictons, which crop out near Toronto and along the north shore of Lake Ontario. It generally has been assumed that middle Wisconsin ice did not extend fully across Lake Ontario, although various researchers have implied that ice did enter portions of the Great Lakes, including the more southerly Lake Erie basin, during that interval. Earlier workers cited evidence for a middle Wisconsin ice incursion into the Cayuga trough (Sixmile Creek), but a range of conflicting 14C ages, including several from the pre-accelerator dating era, created uncertainty over the true age of the sediments and associated events. The Genesee Valley site records two closely spaced advances not apparent in the preserved Sixmile stratigraphy. This recently documented close correspondence in ages between the New York sites and the apparent age of North Atlantic Heinrich event H4 suggest that relatively rapid and short-lived surges best explain the central New York deposits. The Sixmile Creek section extends close to the late Wisconsin Valley Heads moraine position, when ice covered the entire Finger Lake’s region, including the central Genesee Valley. The middle Wisconsin ice margin in the Genesee Valley appears not to have extended quite as far south. Both records suggest that a more detailed Wisconsin history is preserved in Finger Lake troughs. Such an ice advance also places significant limits on the outlets for any lake stages related to the middle Wisconsin Thorncliff formation, associated with a large proglacial lake in the western Lake Ontario basin. This proglacial lake previously was assumed to have drained eastward through the St. Lawrence Valley. The existence of Thorncliff sediments 100 m above present Lake Ontario implies a more complex history with a westerly outlet for part of middle Wisconsin time. Other evidence for middle Wisconsin oscillatory ice advances coincident with H4 have been described from localities such as the Porter Cave site in central Indiana.