The Nature and Origin of the Deposits in Canyons of the Ram Plateau, Northwest Territories, Canada

Abstract

<p>Geomorphological mapping and sediment analysis of unconsolidated deposits in the canyons of Ram Plateau, Mackenzie Mountains, N.W.T was undertaken during the summers of 1976 and 1977. Evidence was found for four major Laurentide ice advances. Ice-dammed proglacial lake phases are associated with each of the latter three.</p> <p>During the early stages of canyon development, a massive ice sheet covered the area (Nahanni Glaciation) depositing a till with shield erratics on the plateau surface. After a lengthy erosional phase, ice passed through breaches in Nahanni Range and advanced to the eastern flank of Ram Plateau (Sundog Glaciation). This impounded Lake Sundog, in Sundog Basin and Ram Canyon, resulting in infilling to 730 m a.s.l. Following a period of extensive dissection, a third ice sheet advanced to Ram Plateau, and alluvium was deposited up to 550 m a.s.l. in Ram Canyon and its tributaries by the impounded Lake Ram. Two stands during withdrawal are evidenced by deposits along the eastern flank of the plateau at 460 m a.s.l and 380 m a.s.l. The most recent ice sheet advanced as far as Nahanni Range (Tetcela Glaciation) and sediment was deposited to 210-275 m a.s.l. in Tetcela Basin by the impounded Lake Tetcela. This ice sheet is attributed to the "Classical" Wisconsinan glacial stade.</p> <p>Because Ram Plateau was situated at the front of the last three fluctuating ice masses, remnants of sediments dating from lakes impounded by pre-Wisconsinan ice sheets are preserved, and there has been enough time since the plateau and canyon areas were glaciated for the effects of glacial scour to have been obliterated and the alluvium to be intensely dissected and massively slumped.</p>