Abstract
Yukon Territory has been repeatedly affected by the northern Cordilleran Ice Sheet. This ice complex produced three irregular, digitate, horseshoe-shaped glacial limits on the plateau area of central Yukon that were thought to be synchronous. However, the penultimate “Reid” glaciation actually represents two separate glaciations. Cosmogenic 10Be ages on boulders of 54-51 ka on penultimate drift in western Yukon Territory confirm that Marine Oxygen Isotope Stage (MIS) 4 (early Wisconsinan) glaciation was extensive in parts of Yukon Territory. These results are in contrast to the MIS 6 (Illinoian age) of the penultimate Reid glaciation to the east in central Yukon, recently confirmed by the presence of Old Crow tephra (124 ka). This dichotomy for at least two of the source areas for the northern portion of the Cordilleran Ice Sheet, indicate different glaciological responses to climatic forcing during glaciations. At sections exposed at the penultimate limit along White River in SW Yukon MIS 4 has an almost identical extent to an older, likely MIS 6 glaciation. Sediments between deposits of these two glaciation preserve abundant plant and insect macrofossils, large mammal bones and tephas allowing reconstruction of paleoenvironments for MIS 5e, 5a and 3.
bio
Brent Ward is a Quaternary Geologist in the Earth Sciences Department at Simon Fraser University. He received his BSc and PhD from the University of Alberta but also spent time at the University of Bergen in 1990. Brent spent three years in Ottawa with the Geological Survey of Canada, mapping in the NWT. In Prince George he studied landslides and slope stability mapping for the Ministry of Forests. He has been at SFU since 1997. Most of his research is in the Canadian Cordillera and focused on resolving glacial history and associated paleoenvironmental reconstructions. His graduate students work in the Canadian Cordillera as well as other parts of northern Canada on projects ranging from terrain and surficial geology mapping, stratigraphy/paleoenvironmental reconstructions and landslides.