Dating early and middle (Reid) pleistocene glaciations in central Yukon bytephrochronology

The late Cenozoic deposits of central Yukon contain numerous distal tephra beds, derived from vents in the Wrangell Mountains and Aleutian arc-Alaska Peninsula region. We use a few of these tephra beds to gain a better unders tanding on the timing of extensive Pleistocene glaciations that affected th is area. Exposures at Fort Selkirk show that the Cordilleran Ice Sheet adva nced close to the outer limit of glaciation about 1.5 myr ago. At the Midni ght Dome Terrace, near Dawson City, exposed outwash gravel, aeolian sand, a nd loess, related to valley glaciers in the adjacent Ogilvie Mountains, are of the same age. Reid glacial deposits at Ash Bend on the Stewart River ar e older than oxygen isotope stage (OIS) 6 and likely of OIS 8 age, that is, about 250,000 yr B.P. Supporting evidence for this chronology comes from m ajor peaks in the rates of terrigeneous sediment input into the Gulf of Ala ska at 1.5 and 0.25 myr B.P. (C) 2001 University of Washington.