RICHARDSON MOUNTAINS, YUKON-NORTHWEST TERRITORIES - THE NORTHERN PORTAL OF THE POSTULATED ICE-FREE CORRIDOR

The Richardson Mountains, located to the east of the Porcupine Plateau and Old Crow Basin, constitute the first barrier that migrating organ isms would have to traverse in order to follow any potential 'Ice-Free Corridor' in western Canada. Two gaps exist in the mountain range: Mc Dougall Pass in the north, and Peel River Canyon in the south. The exi stence of the 'Ice-Free Corridor' in this region thus hinges upon the chronology and extent of Laurentide glacial advances in these areas. T hree glacial events have been recognized in the Richardson Mountains-P eel Plateau region. An initial event occurred during the middle Quater nary, depositing sediments subsequently reworked into the 'Brown Bear' gravels of the central Peel Plateau. A second glacial event occurred at some later time prior to the Late Wisconsinan. This glaciation, cor relative to the Buckland event of the Yukon coastal plain, reached McD ougall Pass, blocking the northern access through the Richardson Mount ains. The glaciation did not extend into the Bonnet Plume Basin, but t he presence of glacial ice in the southern Peel Plateau impounded a la rge lake in the basin, depositing lacustrine sediments and preventing use of the flooded Peel River Canyon route. The most recent major glac iation, of Late Wisconsinan age, was less extensive than the second ev ent in the central and northern Peel Plateau. Although glacial ice did nor penetrate McDougall Pass at this time, lacustrine impoundment in the pass and the Bell Basin precluded use of this route by any potenti al migrants during the Late Wisconsinan. In the Bonnet Plume Basin, La te Wisconsinan ice advanced over the deformable, previously deposited lacustrine sediment, reaching its maximum position at Hungry Creek. Th e southern passage through the Richardson Mountains was blocked by gla cial ice during tie Late Wisconsinan, and thus no suitable gateways to the 'corridor' route existed prior to the ultimate deglaciation of th e region. Copyright (C) 1996 INQUA/Elsevier Science Ltd