Characterising the deglaciation and postglacial Tyrell Sea incursion from mapping of deglacial landforms on the western Ungava Peninsula, Nunavik, Canada

The Labrador Sector was an active component of the Laurentide Ice sheet during the last glacial cycle, with significant migrations its ice divide system and marked changes in its subglacial thermal regime. On the Ungava Peninsula, these changes are highlighted by a mosaic of different glacial landforms and terrains that together outline a succession of landform assemblages arranged symmetrically around the former position of the Payne ice divide. The core area spreads along a north-south axis that is underlain by a thin glacial sediment cover pierced by numerous frost-shattered bedrock outcrops and extensive felsenmeer typical of cold-based ice conditions. This central zone is flanked to the east and west by an unmolded till plain, which gradually changes into a fluted till plain that includes drumlins and crag-and-tails that together indicate a radial ice flow from this ice dispersal center. This latter zone comprises several eskers and associated glaciofluvial deposits. This system terminates at the coastal areas where widespread wave-washed bedrock and/or extensive glaciomarine shorelines and deltas were deposited in the postglacial sea. Deglaciation of the Ungava Peninsula was also complex with asymmetric rates of ice retreat between the eastern (slow) and western (fast) margins and large uncertainties persist on the regional pattern of ice margin retreat as well as on the timing of the deglaciation. Deglaciation of the eastern Hudson Bay coast was marked by the postglacial marine incursion of the Tyrell Sea that led to the formation of a spectacular deglacial landscape characterized by large fields of DeGeer moraines, ice-contact deltas and eskers. Here we use these deglacial features to characterize the nature of ice retreat, geometry of the ice margin configuration and relative chronology of ice withdrawal in the region. We present the first detailed glacial geomorphology map of the northwestern sector of the Ungava Peninsula based on interpretations of high-resolution satellite imagery (RapidEye: 5m; Pléiades: 0.5 m) and extensive fieldwork carried out on the deglacial landscape of the Puvirnituq area on the east coast of Hudson Bay. Our mapping results provide a new high-resolution database of individual deglacial landforms that comprises an exhaustive inventory of DeGeer moraines, which document the nature and style of the regional ice retreat pattern. We also sampled large marine ice-contact deltas for cosmogenic dating at two sites, which are part of an East-West sampling transect aimed at constraining the timing of the deglaciation of the Peninsula. Overall, this work provides a new geomorphological framework that improve our understanding of the ice sheet margin evolution during the final stages of the deglaciation of Nunavik.