TEPHROCHRONOLOGIC CONSTRAINTS ON PRE-WISCONSINAN GLACIAL CHRONOLOGIES IN YUKON AND ALASKA

Over the past ~30 years tephrochronology has played a key role in establishing chronologic frameworks for the non-glaciated regions of Yukon and Alaska. More than 100 tephra beds are known across this region, providing an increasingly robust tephrochronological framework. Recognition of these beds within the glaciated regions of Yukon and Alaska provides new insights the timing of glaciation in this region. Here we examine several examples of the use of tephra beds in dating older (i.e. beyond radiocarbon), problematic glacial sequences. Case studies include: (1) the identification of the Old Crow tephra (124 ± 10 ka) within deglacial sediments associated with the Reid glaciation; (2) the presence of the Mosquito Gulch tephra (1.42 ± 0.16 Ma) in drill-core near Carmacks, Yukon Territory, identifying early Pleistocene glacial activity in this area; and, (3) the GI tephra (560 ± 80 ka) indicating the most extensive glaciation of the Yukon-Tanana Upland occurred during the middle Pleistocene.