Unravelling the fragmented sediment–landform assemblage in an area of thick Quaternary sediment, western Hudson Bay Lowland, Canada

Abstract

Laurentide Ice Sheet (LIS) reconstructions beyond the last glacial maximum (LGM) are difficult due to the incomplete stratigraphic record that has largely been overprinted by the most recent glaciation. The Hudson Bay Lowland (HBL) is a key region to understanding the long-term evolution of the LIS, as it contains an extensive pre-LGM stratigraphic record of glacial and nonglacial events across three or more glacial-interglacial cycles. This study uses a hybrid lithostratigraphy-allostratigraphy approach to decipher the palimpsest stratigraphic record in the Kaskattama highland region of the western HBL, Manitoba, Canada. We identify five glacial (till) units and three nonglacial (sorted sediment) units that were deposited during at least three glacial-interglacial cycles, which are constrained by radiocarbon and optical age datasets. The provenance of till units is identified using clast-lithology, detrital hornblende 40Ar/39Ar ages and supported by matrix geochemistry. The new stratigraphic framework for this western HBL region indicates that the ice emanating from the Quebec-Labrador Dome advanced into the region at the start of the last two glaciations, suggesting accelerated early growth of the Quebec–Labrador Dome relative to the Keewatin Dome.