RECONNAISSANCE MAPPING OF SURFICIAL GEOLOGY IN THE CATSKILL MOUNTAINS OF NEW YORK

The surficial geology of the Upper Esopus drainage basin was investigated during the summer of 2011 by students from the SUNY New Paltz REU program in collaboration with the New York City Department of Environmental Protection (DEP). Esopus Creek empties into the Ashokan Reservoir, a water supply for New York City. Fine sediment sources derived from varved glacio-lacustrine clay and clay-rich tills are causing excessive turbidity. Mapping glacial deposits helps determine the extent and location of fine sediment sources for future DEP remediation work.

LiDAR was used to identify landforms for field observation and determination of origin. Morphostratigraphic units were mapped using GIS software. Overburden stratigraphy was compiled from available well logs and field measurements of exposures. The resulting surficial geologic map of the Upper Esopus refines recent STATEMAP efforts in the Phoenicia quadrangle (De Simone, 2009), Bearsville quadrangle (Kozlowski, open file map), and Shandanken quadrangle (Smith, open file map).

Mapping and stratigraphic interpretation reveals deposits from multiple glacial events. Generalized basin-wide stratigraphy includes a lowermost unit of grey compact till. Lacustrine varved clays, silt and sand overlie this grey till, indicating the former existence of a regional glacial lake. The upper lacustrine contact exhibits shear deformation with faults and folds and grades into a red clay-rich diamicton, evidence of a more recent ice advance. The clay-rich diamicton with small pebbles represents the basal facies of a compact red clay-rich valley till. A thin sandy brown upland till occurs on most valley walls and mountain ridges. Ice-contact sand & gravel deposits are locally present within the field area. Confined rhythmite deposits of silt and sand in some valleys supports the hypothesis of local lakes existing subsequent to the regional lake in the Upper Esopus Drainage Basin. Post-glacial erosion truncates the valley units and caps them with multiple alluvial terraces that step down to modern stream level.