OPTICALLY STIMULATED LUMINESCENCE (OSL) DATING OF GLACIAL SEDIMENT IN CRYSTAL CAVE, WI

Until recently, the chronology of late Wisconsinan glaciation has been confined to radiocarbon dating organic material within glacial deposits, but some of these dates are considered unreliable due to possible contamination by older organic matter (Clayton 1982, Attig, 1985).

Using optically stimulated luminescence (OSL) dating, samples of glacial sediment deposited in a cave system in western Wisconsin yielded optical ages that constrain the St. Croix-Hancock phase of the Late Wisconsinan glaciation. This data shows active sediment deposition from around 24,000 B.P and places the maximum glacial extent of the St. Croix and Chippewa lobes between 20,000 B.P and 17,000 B.P. Previous studies of glacier bed conditions (Attig et al 1989) and aerial photos of ice-wedge polygons (Clayton et al 2001) suggest regional permafrost during this time period. This is supported by the presence of a thin layer of loess over the earlier cave sediment, indicating a possibly a halt in groundwater movement and glacial melt-water deposition.

The consequences of this study show OSL can be an effective dating method not only for glacial outwash, but also for allochthonous cave sediment. It also constitutes as one of the first studies that provide chronological evidence for the Late Wisconsinan glaciation by investigating sediment deposited within a periglacial karst environment.