HR: 0800h
AN: PP11B-1471    [Abstracts]
TI: Quaternary Geology and Glacial Limits of Southern Mackenzie Mountains and Foothills
AU: * Duk-Rodkin, A
EM: adukrodk@NRCan.gc.ca
AF: Geological Survey of Canada, 3303-33rd Street N.W., Calgary, AB T2L 2A7 Canada
AB: The Southern Mackenzie region was glaciated by two ice masses. One was in the Mackenzie Mountains and the other was in the eastern Plains. Stratigraphic and geomorphologic evidence indicate that they developed at different times during Late Pleistocene. The eastern continental ice sheet (Laurentide) advanced over the foothills and up valleys before montane valley glaciers and Cordilleran Ice Sheet reached their maxima, or during initial montane valley glaciation ca. 30 ka. This pattern of glaciation is similar to that which affected central and Northern Mackenzie Mountains. While areas north of 64^o have excellent geomorphic and pre/-Late Pleistocene stratigraphic glacial records the southern areas in contrast have a geomorphic and stratigraphic Late Pleistocene record only. Late Pleistocene glaciation within the Southern Mackenzie region provides evidence for distinct ice sources. The continental ice sheet moved into the region in lobes that sculpted the topography from the foothills to the mountains. The montane glacier suite includes valley glaciers from the continental ice divide, local ice caps, and the Cordilleran Ice Sheet from the southwest. The presence of these montane and continental ice masses caused major landscape changes to the Southern Mackenzie Mountains. Initial Laurentide Ice Sheet advance blocked the drainage of South Nahanni River in the vicinity of Virginia Falls and lower Flat River, causing the formation of a 6000 km² glacial lake. Its outlet was to the southwest into Yukon Territory and the Pacific Ocean. At several sites east of Virginia Falls, the thickness of glaciolacustrine sediments reaches 120 metres. Shield erratics were found over 100 km west of the mountain front. During retreat of the continental ice sheet and advance of montane ice (ca. 22 ka BP), glacial Lake Nahanni cut an outlet to the east at First Canyon. This outlet joined the north flowing meltwater channel system that reached the Arctic Ocean. Another major geomorphic change was the damming of Redstone River. This occurred at ca. 22 k cal yrs BP forcing the eastern flowing river to change its course to the north. The channel crosscuts a folded and faulted terrain triggering ongoing landsliding. These major canyons (now abandoned) indicate that continental ice blocked the mountains creating a meltwater channel system that drained northward across local divides west of the ice front. The last major channel to form was Mackenzie River. The stratigraphic record along the southern Mackenzie Corridor suggests glaciolacustrine and deltaic sediments formed prior to the advancing Laurentide Ice Sheet and were deposited over pre-Late Pleistocene, organic/-rich, overbank sediments. Glaciolacustrine sedimentation was followed by westward and northward continental glaciation that resulted in Laurentide tills, which are overlapped by a second phase of glaciolacustrine sedimentation and another Laurentide till deposited during a readvance. This is overlain by a local montane till devoid of Shield erratics. The final phase was deposition of a mantle of glaciolacustrine and deltaic sediments of glacial Lake Mackenzie. Montane glaciers deposited several interbedded locally/-derived tills in upper North Nahanni River valley. These are overlapped by an outwash gravel terrace. No paleosols are present at their upper contacts and only a change in colour indicates a change in provenance. Neotectonic activity is ongoing and has deformed Late Pleistocene glacial and post-glacial deposits and has triggered landslides, as well as having activated offset faults such as at Virginia Falls.
DE: 0720 Glaciers
DE: 0726 Ice sheets
DE: 0746 Lakes (9345)
DE: 4926 Glacial
DE: 4936 Interglacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005