Title:

COSMOGENIC 36CL DATING OF THE GRANITE CANYON MORAINE COMPLEX IN THE TETON RANGE TO DETERMINE FAULT OFFSET RATES AND THE INFLUENCE OF VALLEY HYPSOMETRY ON GLACIER BEHAVIOR

Mountain ranges in the western United States have repeatedly hosted alpine glaciers during the Quaternary, and records of their fluctuations can provide insight into past climate changes. However, glacier responses to climate shifts remain incompletely understood because there are many complex controls on glacier behavior such as orientation, valley gradient, glacier hypsometry, and ice thickness and slope. Granite Canyon, located in the southern portion of the Teton Range, exhibits a contrasting bedrock lithology, valley hypsometry, and moraine morphology relative to glaciated valleys in the central and northern parts of the range and offers an opportunity to further understand how these geologic factors impact the timing and style of glacial culminations and retreat. In this study, we explore a variety of geomorphic, tectonic, and glacial questions and provide a comprehensive landscape analysis of the Granite Canyon drainage. To do so, we (1) obtain 36Cl and 10Be exposure ages for the Granite Canyon latero-terminal moraine complex, (2) characterize the Granite Canyon valley, paleoglacier hypsometry, and moraine morphology relative to adjacent valleys further north along the eastern Teton range front, and (3) calculate vertical separation of fault scarps on the Granite Canyon lateral moraines and determine cumulative offset rates for the Teton fault since deglaciation. Our results indicate mean ages of 16.4 ka for the terminal moraine, 14.9 ka for the left lateral, and 16.9 ka for the right lateral. We also calculate approximately 11 m of vertical separation on the fault at Granite Canyon with an offset rate of ~1 m/ky since deglaciation. The moraine sequences in Granite Canyon show a similar timing of glacier retreat as the valleys in the central and northern parts of the range (~16 ka), but their morphology suggests a different style of ice recession. Our fault offset rate estimates are consistent with those from previous studies elsewhere in the Teton Range, but this work provides the first direct age control and offset rate estimates for the Granite Canyon moraines. Our results improve our understanding of geomorphic controls on glacier behavior, expand on the paleoseismic history of the Teton fault, and contribute to cross-isotope calibration efforts.

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