NEW STRATIGRAPHIC AND CHRONOLOGICAL CONSTRAINTS IN WESTERN HUDSON BAY LOWLAND, CANADA, AND THEIR IMPLICATIONS FOR THE LAURENTIDE ICE SHEET EVOLUTION

It has been a long-standing question whether the Hudson Bay Lowland (HBL), located near the geographic centre of the Laurentide Ice Sheet (LIS), was deglaciated during MIS 3. Addressing this problem has important implications for our understanding of LIS configuration. Recent studies have documented MIS 3-aged non-glacial sediments in the HBL using radiocarbon and luminescence dating methods. This evidence has been used to imply a reduced LIS extent in the HBL during MIS 3, and possibly a deglaciated Hudson Bay. In the western HBL region of northeast Manitoba, evidence that supports MIS 3 deglaciation is limited to luminescence ages (32–46 ka) from sorted intertill sediments at four sites along the Nelson River and near-finite radiocarbon ages from wood at the Black Duck River site (Manitoba/Ontario border). Based on new stratigraphic and radiocarbon evidence, we show that two of the Nelson River sites – Flamborough and Port Nelson – are older than MIS 3. Furthermore, a refinement of the stratigraphy based on new field-based observations indicates that the Flamborough and Port Nelson sediments were deposited during separate nonglacial intervals. Lastly, preliminary luminescence measurements at the Black Duck River site have yielded an age that falls within MIS 5a, which challenges the current MIS 3 interpretation for these sediments. A review of the currently available chronological constraints on intertill nonglacial deposits across the entire western HBL, including those from our on-going stratigraphic studies, suggest that western HBL was not deglaciated during MIS 3, but was perhaps ice-free during MIS 5a instead.