Richardson Mountains, Yukon-Northwest territories: The northern portal of the postulated ‘Ice-Free Corridor’

Abstract

The Richardson Mountains, located to the east of the Porcupine Plateau and Old Crow Basin, constitute the first barrier that migrating organisms would have to traverse in order to follow any potential ‘Ice-Free Corridor’ in western Canada. Two gaps exist in the mountain range: McDougall Pass in the north, and Peel River Canyon in the south. The existence of the ‘Ice-Free Corridor’ in this region thus hinges upon the chronology and extent of Laurentide glacial advances in these areas. Three glacial events have been recognized in the Richardson Mountains-Peel Plateau region. An initial event occurred during the middle Quaternary, 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, correlative to the Buckland event of the Yukon coastal plain, reached McDougall Pass, blocking the northern access through the Richardson Mountains. The glaciation did not extend into the Bonnet Plume Basin, but the presence of glacial ice in the southern Peel Plateau impounded a large lake in the basin, depositing lacustrine sediments and preventing use of the flooded Peel River Canyon route. The most recent major glaciation, of Late Wisconsinan age, was less extensive than the second event in the central and northern Peel Plateau. Although glacial ice did not penetrate McDougall Pass at this time, lacustrine impoundment in the pass and the Bell Basin precluded use of this route by any potential migrants during the Late Wisconsinan. In the Bonnet Plume Basin, Late Wisconsinan ice advanced over the deformable, previously deposited lacustrine sediment, reaching its maximum position at Hungry Creek. The southern passage through the Richardson Mountains was blocked by glacial ice during the Late Wisconsinan, and thus no suitable gateways to the ‘corridor’ route existed prior to the ultimate deglaciation of the region.