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Evidence for a 55-50 ka (early Wisconsin) glaciation of the Cordilleran ice sheet, Yukon Territory, Canada |
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| Authors: | Brent C Ward Jeffrey D Bond |
| Institution: | a Department of Earth Science, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 b Yukon Geological Survey, P.O. Box 2703, Whitehorse, Yukon, Canada Y1A 1B5 c Department of Earth Sciences, 3006 LSC, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3G5 |
| Abstract: | Cosmogenic 10Be ages on boulders of 54-51 ka (n = 4) on a penultimate Cordilleran ice sheet (CIS) drift confirm that Marine Oxygen Isotope Stage (MIS) 4 (early Wisconsin) glaciation was extensive in parts of Yukon Territory, the first confirmed evidence in the Canadian Cordillera. We name the glaciation inferred from the mapped and dated drift the Gladstone. These results are in apparent contrast to the MIS 6 (Illinoian) age of the penultimate Reid glaciation to the east in central Yukon but are equivalent to exposure ages on MIS 4 drift in Alaska. Contrasting penultimate ice extents in Yukon requires that different source areas of the northern CIS in Yukon responded differently to climatic forcing during glaciations. The variation in glacier extent for different source areas likely relates to variation in precipitation during glaciation, as the northern CIS was a precipitation-limited system. Causes for a variation in precipitation remain unclear but likely involve the style of precipitation delivery over the St. Elias Mountains possibly related to variations in the Aleutian low. |
| Keywords: | Cordilleran ice sheet Glacial extent Cosmogenic nuclides Dating Precipitation |
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