The northern Mackenzie Valley and the Beaufort Coastlands Region lie between 64° and 71°N, and 128° and 141°W. The land features are generalized in this perspective view which shows the location of the mountains, uplands, river valleys and coastal plains in the area. Except for the westerly draining Old Crow Basin, the regional drainage is part of the Mackenzie River Basin. This system drains about 16% of the Canadian landmass and is a major support for wildlife and people in this region.

Landscape Evolution in Northwestern Canada

The modern landscape in Northwestern Canada has inherited features from as early as upper Cretaceous time almost 80 million years (Ma) ago. The level or gently rolling areas of the Mackenzie Valley are underlain by shale deposited in a Late Cretaceous seaway that occupied most of the western interior plains. The uplift of the mountains since early Tertiary time (about 65 Ma ago) and subsequent cycles of erosion and downcutting have formed extensive piedmont areas extending to the Canadian Shield. Rivers followed the general slope to the east, northeast and north, flowing radially away from the highlands. However, within the mountains the drainage is structurally controlled and, in most cases, rivers run parallel with the mountain front. During most of the Tertiary the northern Cordillera was the headwater of drainage systems that reached three oceans: the Arctic (Peel-Anderson, Porcupine, since Eocene), the Atlantic (Bell River, since the Paleocene) and the Pacific (Yukon River exiting the Gulf of Alaska, at least since the Miocene).

Global deterioration of climate triggered glaciations which affected northwestern Canada starting about 3 million years ago (ca 3 Ma B.P.). Evidence in this region of Canada points to glacial events occurring as cordilleran and montane glaciations from late early Pliocene until the Late Pleistocene (Late Wisconsinan). In addition to the cordilleran and montane glaciers this region was visited by the continental ice sheet (Laurentide Ice Sheet) at that time. The Laurentide Ice Sheet reached its maximum extent ca 30 k B.P. and by 13 k B.P., it was not far from its maximum at 400 m below maximum elevation about 70 km to the east. Arctic Red, Ontaratue, Mountain rivers including the Mackenzie River were established in their present day drainage as ice marginal or outlet channels of proglacial lakes impounded by the Late Wisconsinan Laurentide Ice Sheet. The northern major tributary to the Bell River system was diverted permanently to the Arctic Ocean as the Mackenzie River ca 12 k B.P.

Overall, the landscape in this region including the unglaciated areas is directly the result of glacial and proglacial activity.

Author: A. Duk-Rodkin
Geological Survey of Canada