DEGLACIATION OF THE SOUTHEAST MARGIN OF THE LAURENTIDE ICE SHEET IN NORTHEAST PENNSYLVANIA

Northeast Pennsylvania lakes contain continuous archives of Laurentide Ice Sheet (LIS) deglaciation and postglacial environmental conditions. Here, we present multiproxy glacier and paleoenvironmental records from two lakes in Luzerne County that document retreat from the LIS southeast margin. Nuangola Lake (41.159º N, 75.974º W, 356 m ASL) and Cranberry Pond (41.146° N, 76.059° W, 311 m ASL) are relatively small, shallow (depth < 10 m) glacial lakes located approximately 10 kilometers north of the Last Glacial Maximum terminal moraine. We collected overlapping sediment cores from both lakes and characterized the sediments using a multi-proxy approach. We imaged the cores and measured visible reflectance, dry bulk density, organic matter via loss-on-ignition, magnetic susceptibility, and biogenic silica. Age control for the sediment sequences is developed using a combination of radiocarbon dates on terrestrial macrofossils and geochemical analysis of cryptotephra deposits.

Sediment cores from both lakes are divided into three similar and distinct lithofacies consisting of basal glaciolacustrine (varved) sediments, overlain by transitional minerogenic sediments, and capped by organic rich post glacial sediments. A basal radiocarbon age above the varve transition indicates deglaciation of the Nuangola Lake basin occurred sometime prior to ~ 19,200 cal yr BP. The subsequent transition to organic rich post glacial sediments, constrained by multiple radiocarbon ages in the Nuangola cores, occurred ~ 15,000 cal yr BP. Macrofossil materials from the Cranberry Pond cores were much less abundant, but our bracketing dates confirm the approximate timing of the post glacial sediment transition. The inferred timing of deglaciation is substantially younger than estimates developed from cosmogenic exposure dates on terminal moraine boulders from adjacent states. We will explore our results in the context of other regional glacial-geologic records to better understand the dynamics of LIS deglaciation for northeast Pennsylvania and adjacent regions.