Abstract

Measurements at some 300 cross-striated sites in the Abitibi–Timiskaming area of Quebec and Ontario revealed two former directions of ice flow: an older west-southwest one (230–270°) in the extreme western part of the area, and a younger, widespread south-southwest one (180–220°) in the region west of the Harricana – Lake McConnell glaciofluvial complex. These sets of older striae, whether one or both on the same outcrop, are almost everywhere crossed by marks of a younger ubiquitous flow to the south-southeast (130–170°). On the basis of striae directions measured below an older till and of three dates obtained from intertill (below the surficial till) nonglacial sediments in the Timmins and Matheson areas in Ontario and the Selbaie mine area in Quebec, the oldest west-southwest (230–270°) striae are tentatively associated with the west-southwest flow that deposited this lowermost till in early to mid-Wisconsinan time or earlier.The Harricana – Lake McConnell glaciofluvial system extends from James Bay to the vicinity of North Bay Ontario and probably continues farther south to the Lake Simcoe area. It is strictly an interlobate deglaciation feature and does not result from the converging flows of two coalescing glaciers. At the last glacial maximum the dominant ice-flow direction in the area was probably toward the southwest, across the space occupied by this glaciofluvial system, confirming the flow lines shown by most models of the late Wisconsinan ice sheet. Because none of the cross-striated outcrops showing marks of the former south-southwest (180–220°) and of the last south-southeast (130–170°) movements show evidence of differential weathering and because glacial transport was due to the former southwest movement at several locations, it is proposed that the cross-striations result from the same ice mass subjected to (1) a general change in flow direction from the southwest to the southeast and (2) a complete scission that led ultimately to the deposition of the Harricana – Lake McConnell glaciofluvial system in the interlobate position.

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