GREAT GULLY REVISITED: NEW CONSTRAINTS ON THE GLACIAL CHRONOLOGY OF THE CENTRAL NEW YORK FINGER LAKES

Long regarded as a premiere example of glaciated landscapes, the Finger Lakes in Central /Western New York State have captivated the attention of quaternary geologists for more than 100 years. Yet their origins have long been debated and chronologic evidence to help support or dismiss multiple hypotheses has remained elusive.

It is generally accepted that the Ontario Lobe of the Laurentide Ice sheet during the Late Wisconsin is responsible for the present landscape observed in the Finger Lakes region. Moreover, as the lowest north-south oriented axial depression in Central New York, the Cayuga Lake Basin would/will be the recipient of any and all invasions of continental glacial ice extending into the Southern Tier of New York. Such intrusions presumably create a record of glacial onset, phases of retreat and high elevation proglacial lakes constrained by ice margins such as the Valley Heads Moraine. Follow up investigations to a 1957 study, as part of an ongoing geologic mapping project in Cayuga County, provide new sedimentologic and stratigraphic data that allows us to reevaluate the proposed glacial chronology and geomorphic origins of the Finger Lakes Region during the Late Pleistocene.

Four kilometers south of Union Springs, NY stratigraphic sections of glacial deposits in excess of 34 meters in height preserved in Great Gully, a prominent deeply incised westward draining ravine, oriented perpendicular to the Cayuga Trough comprise of multiple diamicton units interpreted as glacial tills. Tills are underlain by laterally continuous, correlative fluvial and laminated lacustrine facies. Paleo-flow reconstructions on sedimentary structures within deeply buried fluvial and lacustrine facies indicate drainage into an open-system within the Cayuga Lake Basin. Collectively the deposits observed are interpreted to represent multiple glacial cycles. Radiocarbon dates on sub-till organics, recovered in the fluvial and lacustrine facies combined with optically stimulated luminescence (OSL) dating provide robust, internally consistent chronologic data that document a record of glacial fluctuations into the Cayuga Trough extending to at least marine isotope stage (MIS 5). This new chronologic anchor point provides a long sought after tool for regional correlation within the Great Lakes Region.