EXPANDED CHRONOLOGY OF LATE PLEISTOCENE GLACIAL EVENTS IN THE GREATER YELLOWSTONE AND GRAND TETON REGIONS

Records of the greater Yellowstone-Teton Range glacier systems have long served as a foundation for understanding the timing of the last (Pinedale) and penultimate (Bull Lake) glaciations for much of the Rocky Mountains. In previous investigations, we obtained >110 cosmogenic ³He and ¹⁰Be surface exposure ages from boulders on moraines deposited by glaciers in the Yellowstone and Grand Teton regions during the middle and late Pleistocene. These prior dating efforts established a high-resolution chronology of the Yellowstone-Teton mountain glacier complexes, but crucial aspects of the regional glacial history remain incompletely understood. For example, it is unclear whether valley glaciers in different drainages on the eastern and western sides of the Teton Range behaved synchronously. Previously developed exposure age data in Grand Teton National Park are restricted to the Cascade Canyon / Jenny Lake drainage, and therefore cannot address this question. Here we expand on the geographic coverage of prior glacial-geologic research by applying ¹⁰Be exposure dating to glacial deposits in several drainages along the eastern Teton range front. Our new investigations are focused on moraines and scoured bedrock surfaces at Glacier Gulch, Avalanche Canyon, Taggart Lake, Phelps Lake, Granite Canyon, and adjacent areas. Ages are also being developed from sampled moraine boulders along a position corresponding to the Pinedale 2 phase of the southern margin of the greater Yellowstone glacial system, as well as on the west side of the Teton range crest. The expanded chronology will contribute toward an understanding of both the timing of late Pleistocene glacier events in the western U.S. and the predominant climatic influences on glaciation. Refinements in the glacial history will also provide critically important context for understanding rates and patterns of biotic responses and ecological changes during the transition from glacial to interglacial conditions.