ABSTRACT: Yukon and Mackenzie river systems: Glacially diverted drainages resulting from the first Cordilleran glaciation and the last continental ice sheet.

CGRG Bibliography of Canadian Geomorphology
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Abstract

The modern landscape of NW Canada contains inherited features, some of which date back to upper Cretaceous. Since late Cretaceous-early Tertiary, uplift of the mountains and subsequent cycles of erosion have formed extensive piedmonts extending eastward to the Canadian shield. In general, the northern Cordilleran drainage is structurally controlled. During most of the Tertiary, the northern Cordillera formed the headwater for drainage systems that reached three oceans: the Arctic (Peel-Anderson and Porcupine Rivers), Atlantic (Bell River system) and Pacific (Yukon River draining into the Gulf of Alaska). The arrival of ice sheets produced significant changes to the landscapes of N.W. Canada and east central Alaska. The most important was the diversion of the Yukon River to the northwest into the Kwikhpak River in Alaska. The first Cordilleran Ice Sheet (ca 2.7 Ma) blocked the Yukon River drainage, reversing its flow (from south to north and emptying instead into the Beaufort Sea). Evidence for this is found in the paleo-terraces extending south out of the Ogilvie Mountains, whose gravels reveal a southerly flow and contain Ogilvie lithologies. The Pliocene outwash terraces near Circle Alaska provide the earliest evidence of Ogilvie Mountain lithologies and thus indicate that sediment input into the Yukon Flats area dates to the Pliocene.The Late Pleistocene Laurentide Ice Sheet covered the Mackenzie region and changed the Cordilleran landscape dramatically by diverting the Porcupine River into its present location and by integrating the Mackenzie River to its present day location, ca 12 k BP. This integration of drainage was established as a result of deglaciation, where most of the major tributaries of the Mackenzie River north of 65° latitude were incised as meltwater channels. The paleo-Mackenzie River was the major northern tributary of the Bell River system which drained the Western Interior Plains to the Labrador Sea via Hudson Bay. Evidence for this paleo-drainage is contained in the suite of terrestrial sediments in the Labrador Sea. After the demise of the continental ice sheet little remained of the original landscape of the northern Interior Plains and only a few remnants of alluvial deposits belonging to this preglacial drainage are found. In the last three million years the transformation of the landscape by glaciers has reduced the number of drainage basins entering the three adjacent oceans, from five to two.

Bibliography of Canadian Geomorphology