EVIDENCE FROM THERMOLUMINESCENCE DATING FOR MIDDLE WISCONSINAN DEGLACIATION IN THE HUDSON-BAY LOWLAND OF MANITOBA

We report here the first direct dating of the nonglacial, intertill Nelson River sediments from five sites in northern Manitoba. We used the thermoluminescence (TL) sediment-dating technique to obtain age estimates of 32-46 ka for four samples and 119 ka for the fifth, all samples previously correlated to the Sangamonian Stage (80-130 ka) Missinaibi Formation. We interpret the younger TL dates as being within 20-40% of the true deposition ages, but interpret the oldest TL date as an overestimate because of ineffective zeroing of the light-sensitive TL associated with observed pebble and sand detritus in that sample. Thus these younger direct dates imply a significant climatic warming and deglaciation in the heart of the Laurentide Ice Sheet area during Middle Wisconsinan time.