Abstract

South Nahanni National Park transects the southern Mackenzie Mountains from a position close to the continental divide to their eastern limit. In the context of glaciation it displays three distinct zones: I, in the west, a cordilleran glacial zone with evidence of two or more phases of valley glaciation; II, in the east, a Laurentide glacial zone with evidence of invasion by three successive Laurentide ice sheets; III, a central unglaciated zone. Lacustrine deposits of two distinct phases extend into all three zones and are attributed to ice damming during the last two Laurentide glacial incursions.Stratigraphic studies of caves of the area, incorporating 230Th/234U age determinations of calcite speleothems, indicate that the earliest Laurentide incursion occurred before (350) 320 000 y BP, the others after 190 000 y BP. Events of the two glacial zones are correlated and it is suggested that there was only one major glacial event in each zone during the Illinoisan Glacial and Wisconsinan Glacial.

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