| Summary: | The regional distribution of Holocene sediments of eastern Hudson Bay off the Great Whale River mouth was mapped using a grid of reflection seismic lines over 60 km long and covering an area of approximately 800 km$ sp2$ and data from eight piston cores. A larger data base and a greater area of study than that used in previous studies significantly increases our understanding of the sedimentation and deglaciation processes that have occurred in the area since the last deglaciation. Based on the seismic records and piston cores, four stratigraphic units overlying the Proterozoic bedrock (unit 1) were defined and interpreted: unit 2, glacial till deposited by a westward flowing ice sheet; unit 3, glaciolacustrine stratified muds deposited in glacial Lake Ojibway; unit 4, postglacial marine muds deposited in Tyrell Sea; unit 5, distal fluvio-deltaic sediments from the Great Whale River. Textural and geochemical analyses of individual laminae suggest that unit 3 rhythmites are true varves; dark "summer" laminae were deposited mainly by underflows during the open water season, and light "winter" laminae were deposited by overflows-interflows under a seasonal ice cover. Unit 5 covers approximately 400 km$ sp2$ and occurs as a deltaic constructional wedge which reaches 11 km offshore of the Great Whale River entrance. It was deposited between 3500 BP and 2800 BP from material supplied by the erosion of the Sakami Moraine and of glaciolacustrine and marine muds exposed along the river banks.
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