Quaternary Glaciations of the White River Valley, Alaska, with a Regional Synthesis for the Northern St. Elias Mountains, Alaska and Yukon Territory

摘要

During Quaternary ice ages, a complex piedmont glacier repeatedly formed north of the St. Elias Mountains in Yukon Territory and Alaska. During the Macauley glaciation (the youngest), the White River valley in Alaska served as a conduit of ice that filled the valley to thicknesses of 850 to 1,150 ft (256 to 351 m) and flowed eastward into Yukon Territory, where it fed the western margin of the Macauley piedmont glacier. C14 dates fail to pinpoint Macauley expansion in the valley, but they do indicate deglaciation by 11,270 yr B.P. and subsequent spruce immigration by 8,020 yr B.P. On as many as five occasions prior to 37,000 yr B.P., pre-Macauley ice filled the valley; on at least three occasions, it spilled northward over the valley rim. Along its upper surface, Macauley drift in the White River valley and in the adjacent Snag-Klutlan area (Rampton, 1971a) can be traced into Kluane Drift exposed farther east near Kluane Lake (Denton and Stuiver, 1966, 1967), thus permitting reconstruction of the Macauley-Kluane piedmont glacier. Near Kluane Lake, the main Kluane ice advance postdated 29,600 yr B.P., but the initial Macauley advance in the Snag-Klutlan area is not associated with finite C14 dates. The maximum Macauley-Kluane ice extent was attained near Snag about 14,000 yr B.P. (Rampton, 1971a); subsequent recession was very rapid. Prior to the Kluane glaciation, Shakwak Trench was deglaciated to the vicinity of Kluane Lake during the Boutellier nonglacial interval (49,000 yr B.P.). Whether similar recession characterized the Snag-Klutlan area and White River valley is not known. The earlier Icefield glaciation (>49,000 yr B.P. near Kluane Lake) correlates with, or is younger than, the Mirror Creek glaciation (>38,000 yr B.P. in the Snag-Klutlan area). The still older Silver nonglacial interval and the Shakwak glaciation in the Kluane Lake area cannot be correlated now with other St. Elias events. Nor can pre-Macauley glaciations in the White River valley be correlated yet on a regional basis. The most striking late Wisconsin event in the St. Elias Mountains was the nearly complete disintegration of Macauley-Kluane ice within only 1,500 to 2,700 yr after attaining its maximum about 14,000 yr B.P. Several other alpine glacier systems in cordilleran North and South America showed similar rapid recession, as did larger ice sheets to a less marked degree. Quite possibly, the behavior of these sensitive alpine glaciers reflects an abrupt background climatic event that essentially terminated the late Wisconsin glaciation shortly after 14,000 yr ago. These data indicate that Termination I of Broecker and van Donk (1970) began shortly after 14,000 yr B.P. The glacial chronology of the northern St. Elias Mountains suggests that early man could have inhabited Shakwak Trench, perhaps using it as a route to British Columbia or coastal southeastern Alaska, during the Boutellier nonglacial interval, and again by 11,000 to 12,000 yr B.P. at the end of the Kluane-Macauley glaciation.