Hudson Bay Lowland Quaternary stratigraphy; evidence for early Wisconsinan glaciation centered in Quebec

Information from river sections in the Hudson Bay lowland indicates that two pre-Holocene nonglacial episodes separated by glacial advances postdate the oldest recognized glaciation. Amino-acid data from in situ and transported marine shell fragments provide relative ages for glacial and nonglacial intervals. Absolute ages for non-glacial sediments as recent as mid-stage 3 were obtained from thermoluminescence (TL) data, although no finite radiocarbon ages have been obtained from wood. Deglaciation and deposition of the Bell Sea marine sediments are correlated to substage 5e by extrapolation from TL data. Ensuing stage 5 glaciation was dominated in Ontario by west-northwestward ice flow emanating from Quebec, and in Manitoba by southwestward ice flow. Deglaciation dated by TL at about 75 ka was followed by isostatic recovery and subaerial exposure in a climate which could have been warmer, but was no more than slightly colder than present. Extensive glaciolacustrine sediments deposited at the close of this interstade were TL dated at about 40 ka in Manitoba. If the TL method has systematically underestimated age, glaciolacustrine sedimentation may date to very late stage 5 or stage 4, or the two nonglacial episodes could be reassigned to substage 5e and stage 7. A resurgence of Quebec-derived ice that culminated as late Wisconsinan glaciation first flowed westward across the entire lowland, but was displaced in the north by southward ice flow. Southwestward and, locally, southward ice flow occurred during final ice retreat along a saddle extending across Hudson Bay and linking domes in Keewatin and Quebec.