STATUS OF QUATERNARY SURFACE AND SUBSURFACE MAPPING IN TOMPKINS COUNTY, NEW YORK AND SURROUNDING AREAS

Beginning in 2018, the New York State Museum – Geological Survey (NYSM-GS) initiated stratigraphic and surface materials mapping investigation of the 12 individual 7.5-Minute quadrangles in Tompkins County. Mapping is sponsored by the National Cooperative Geologic Mapping -StateMap and Great Lakes Geological Mapping Coalition programs of the United States Geological Survey. Prior mapping by geologists determined three distinct geomorphological features of ice-proximal, outwash and glaciolacustrine deposits across the county. Evidence for multiple high-elevation pro-glacial lakes, previous-glacial and non-glacial deposits and new lithologic units was determined from the collection of over 700 soil samples and nine continuous wireline mud-rotary soil borings collected over the culmination of five years of stratigraphic mapping.

Tompkins County lies in the Central Finger Lakes Region of New York State and contains multiple, deeply incised glacially eroded valleys through the Paleozoic Age rocks of the Allegheny Plateau. The most prominent of these valleys is the Cayuga Basin, which dissects through the center of Tompkins County from North to South. This trough is the lowest in elevation and has been The Ontario Lobe of the Laurentide Ice Sheet advanced through the county, terminating at the Valley Heads Moraine along the modern drainage divide between the Lake Ontario and Chesapeake Bay watersheds. Each of the separate VHM moraines lie within basins filled with thick accumulations of glacial drift. The soil cores collected determined the thickness of multiple aquifer layers within sand and gravel outwash, separated by thick accumulations of glaciolacustrine silt and clay or glacial till.

A goal of this investigation is to delineate the extent of, types of, and the age of deposition for these sediment deposits throughout the county and its surrounding region. Employing the use of Optically Stimulated luminescence (OSL) of sand deposits and AMS radiocarbon dating on organics collected during field mapping and soil cores will be used to bracket the timing of glacial events, especially of the movement of the Ontario Lobe within the Tompkins County area, during the Pleistocene Epoch