NEW CONSTRAINTS ON LATE PLEISTOCENE VALLEY GLACIERS IN THE ADIRONDACK HIGH PEAKS REGION, NEW YORK

An interval of local valley glaciation after the late Wisconsinan retreat of the Laurentide Ice Sheet (LIS) has long been proposed for the Adirondack High Peaks region. Here we report on stratigraphy and landforms at Styles Brook, a site in Keene Valley where surficial deposits previously have been attributed to a local valley glacier at least nine kilometers long. Bluffs in the lower Styles Brook valley, recently exposed by erosion associated with Tropical Storm Irene flooding, reveal interbedded diamictons and glacilacustrine deposits of an ice-proximal delta or subaqueous fan. Slickensides, ball-and-pillow structures, folds, and faults all indicate considerable syndepositional movement as the delta/fan prograded southwestward into Glacial Lake Chapel, an ice-contact lake that was impounded in the southern Keene Valley by the retreating LIS. Sediment in the delta/fan originated from the Clements Mountain area on the north side of Styles Brook where the LIS margin may have temporarily stabilized due to a topographic constriction in Keene Valley.

Nowhere within the deposits was unequivocal evidence found for lodgement till or other indicators of deposition from a local valley glacier. A delta on the landsurface near the study site precludes advance of a local glacier after drainage of Glacial Lake Chapel and subsequent lower-elevation lakes, and topographic considerations of the Styles Brook valley suggest that this area was unfavorable for formation of a valley glacier. These results are similar to our previous results at White Brook on the Whiteface-Esther massif and at High Bank on the east side of Giant Mountain, where purported local glacier deposits can all be satisfactorily attributed to the LIS and its proglacial lakes. Collectively these results suggest that kilometers-long valley glaciers did not develop in the Adirondack High Peaks following retreat of the LIS in the late Wisconsinan. This is noteworthy because this area was deglaciated immediately prior to the Younger Dryas, suggesting that a lack of moisture during this cold event may have prevented the formation of large valley glaciers in the Adirondacks.