THE HARTWOOD MORAINE AND ASSOCIATED LANDFORMS IN SOUTHEASTERN NEW YORK STATE: A PREVIOUSLY UNRECOGNIZED HUDSON LOBE ICE-MARGIN OF THE LAURENTIDE ICE SHEET

Geological mapping as part of the National Parks Resource Inventory project in the Upper Delaware River Basin Scenic Area of Sullivan County, and ongoing mapping sponsored by the Great Lakes Geological Mapping Coalition in Orange County, has revealed large, extensive moraines and associated landforms previously unrecognized. The study area is situated in New York State, in the southern Catskill Mountains.

New lidar elevation data reveals a series of distinct, large linear landforms, oriented northeast-to-southwest, draped along the upland bedrock topography composed of Devonian clastic rocks. These landforms have steep, well-defined edges, and hummocky surface topography dominated in places by boulder-lags, and are interpreted as moraines formed along the western edge of the Hudson Lobe of the Laurentide Ice Sheet (LIS). The westernmost landform is designated here as the Hartwood Moraine and spans more than one-half kilometer in width in certain locations. This landform is traceable for more than 40 kilometers from the Pennsylvania border to slightly north of Monticello, NY. A second landform, designated as the Wolf Lake Moraine, aligns parallel to the Hartwood Moraine five kilometers to the east. It is slightly narrower in width and appears to be in a recessional position.

A hanging delta at the confluence of the Mongaup and Delaware Rivers demarcates the location of an ice-dammed lake in the Delaware River Valley created by the emplacement of the Hartwood Moraine. Two OSL ages collected in the topsets of the delta yielded an average age of 25.0 ± 1.5 ka, suggesting a marine isotope stage (MIS) 2 age for the emplacement of the Hartwood Moraine. Another quarry eight kilometers north and west also displayed stratified and well-sorted sand deposits consistent with a delta building into a proglacial lake. However, multiple OSL ages on these deposits indicate sediment burial occurred much earlier, possibly during MIS 4 or MIS 6 glacial cycles, and additional OSL ages are pending. Additional dating and mapping will allow for correlation with other moraines in the region and LIS reconstructions.