AGE OF AN ICE DAMMED LAKE ON THE LEE SIDE OF THE CATSKILL MOUNTAINS, NEW YORK, AND ROUGH ESTIMATES FOR THE RATE OF ICE ADVANCE TO THE LAST GLACIAL MAXIMUM

Hurricane Irene flood exposures in the Upper Esopus Creek basin south of the Schoharie Creek drainage divide and Hunter Mountain in the Catskill Mountains of New York State revealed two distinct varved glacial-lacustrine units. Each varve sequence is deformed at the top and overlain by clay-rich till. The older lacustrine unit is primarily silt and clay with some sand and is significantly compacted, while the younger unit is primarily silt and sand and is not compacted. Numerous exposures and subsurface data indicate that the older lacustrine unit generally occurs basin-wide while the younger unit is restricted to one sub-basin. Our interpretation is that the older unit represents a lake dammed in the eastward draining basin by an ice lobe advancing southward down the Hudson Valley. The lake was subsequently overridden as the Laurentide Ice Sheet advanced across the Catskills towards the Last Glacial Maximum. Our model is strengthened by a pre-LGM Optically Stimulated Luminescence age on quartz sand grains from the varves. Single aliquot analysis produced an age of 27,580 ± 740 years (1 σ). The younger lacustrine unit likely formed locally during ice retreat from the LGM and was overrun by a minor re-advance. An OSL age of 83,330 ± 2,620 years suggests that grains in the younger varves were not subaerially exposed during deposition.

If the older lacustrine unit age is correct, and assuming an LGM age of 24,000 ybp, then we estimate an ice advance rate through southern New York and New Jersey of about 40 m/yr. Recent investigations in Québec by Parent et al. (2015) indicate that the region south of the St. Narcisse Moraine was ice free as late as ~ 35,000 calibrated ybp. This suggests a maximum ice advance rate through southern Québec and northern New York of about 60 m/yr.