GLACIAL LAKE NANETTE: A MIDDLE WISCONSIN (MIS 4 – 3) PROGLACIAL LAKE IN THE CAYUGA BASIN

The Cayuga Basin has long been recognized as a vessel that held expansive proglacial lakes generated as the Ontario Lobe of the Laurentide Ice Sheet advanced southward and dammed northern outlets. Numerous proglacial Lakes at various elevations have been recognized from post Nissouri Phase (MIS 2) deglaciation. The earlier record of glacial events in the eastern Finger Lakes has been studied less and thus are not well known.

Deposits exposed along the valley walls of Great Gully on the eastern flank of the Cayuga Lake, near the Village of Union Springs record the presence of glacial and non-glacial phases collectively recognized as the Great Gully Group. The Aurora Formation occurs mid-group and contains laterally continuous ripple cross-bedded fine-medium grained sands. Abundant organic material preserved in the sands includes macrofossil assemblages that include woody taxa, emergent nearshore and upland taxa and submerged taxa consistent with low energy fluvial-lacustrine depositional environment. Collectively the taxa from the sand units suggest temperatures above subarctic conditions. Thin diamicton units interpreted as tills also occur in this formation and suggest oscillating glacial conditions interrupted by north flowing drainage into the Cayuga Basin. Optically stimulated luminescence dates on the sand units indicate this lake system was established by ~65,000 Cal yr BP.

Stratigraphically above is the Bunker Formation that contains indurated compressed peat and interbedded sand units and spruce wood fragments. These peat deposits suggest a stabilized lake level by about 50,000 Cal yr BP, taxa and pollen suggest cooler environments approaching boreal forest conditions. The peat deposits are truncated and overridden by till deposits generated by a younger readvance occurring prior to 30,000 Cal yr BP.

Continuous wire-line cores substantiate continuity of lacustrine and peat deposits within a previously unknown buried valley system extending more than 8 km in length and 1.5 km in width. The buried valley system appears as a southeastern extension or embayment to the Cayuga Trough. The lake system represented temporally and spatially by deposits is designated as glacial Lake Nanette. This phase represents a high elevation lake present within the Cayuga Basin for most of Marine Isotope Stages (MIS) 3-4.