Abstract

Marine and continental records indicate that the Laurentide Ice Sheet (LIS) was highly dynamic throughout the last glacial cycle, with significant reorganizations of its ice divide system. The extensive depositional record of the Hudson Bay lowlands (HBL) is particularly important for the study of ice sheet dynamics because this region was once located near two important ice domes of the LIS. However, important stratigraphic issues remain in the HBL, notably regarding the chronology of nonglacial units and the direction and extent of the ice-flow events recognized. Here we focus on the northeastern sector of the LIS by documenting the provenance of tills and dating nonglacial deposits in sedimentary sequences east of James Bay. Our investigations indicate that the regional stratigraphy comprises at least five distinct tills and an important unit of glaciolacustrine rhythmites. This glacial sequence lies on massive lacustrine clay and fluvial sand containing abundant organic debris and wood fragments. The clast lithology and matrix geochemistry of tills show significant variations that are consistent with the ice-flow movements deduced from clast fabric measurements. Taken together, the till compositional and fabric data suggest an early westward ice flow, followed by a counterclockwise shift to a west-southwest, southwest, and then south-southeast ice flows. Luminescence dating of waterlaid sediments outlines a complex and fragmentary stratigraphic record, which comprises two distinct nonglacial units belonging to the last and penultimate interglaciations. These results and stratigraphic considerations indicate that the documented ice-flow rearrangements likely occurred during the last glacial cycle.

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