Abstract

Drift morphology and stratigraphic relations of drift sheets and weathering zones indicate four glaciations separated by three nonglacial intervals in the northeastern St. Elias Mountains, Yukon Territory, Canada. Ice of the two oldest glaciations (Shakwak and Icefield) flowed through Slims River valley into Shakwak Valley near Kluane Lake. Ice of the subsequent glaciation (Kluane) entered Shakwak Valley through valleys draining the Icefield Ranges, flowed northwest along Shakwak Valley with a thickness locally exceeding 3530 feet, and terminated in the vicinity of Snag near the Yukon-Alaska boundary. The last glaciation (Neoglaciation) was much more restricted. During the two oldest nonglacial intervals (Silver and Boutellier), Shakwak Valley was ice-free; during the third non-glacial interval (Slims), ice receded more than 13 miles upvalley from the present Kaskawulsh Glacier terminus.

Twenty C14 dates combine to give the following late Pleistocene chronology in the areas studied: Shakwak glaciation (>49,000 B.P.), Silver non-glacial interval (>49,000 B.P.), Icefield glaciation (start >49,000 B.P., end approximately 37,700 B.P.), Boutellier nonglacial interval (start approximately 37,700 B.P., end <30,100 B.P.), Kluane glaciation (start <30,100 B.P., end approximately 12,500-9780 B.P.), Slims nonglacial interval (start approximately 12,500-9780 B.P., end approximately 2640 B.P.), Neoglaciation (start approximately 2640 B.P., still current).

Comparison of C14-dated glacial events in Yukon-Alaska (as recorded in the St. Elias Mountains and in the Brooks Range) with glacial events in Washington and British Columbia, pluvial events at Searles Lake, California, and fluctuations of the Laurentide Ice Sheet in the Great Lakes region suggests, with reservations, that some major late Wisconsin climatic fluctuations in Yukon-Alaska and these other regions were broadly synchronous. However, sufficient detail is not yet available to make firm conclusions about correlation of minor climatic fluctuations during these times.

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