EXTENSIVE GLACIATION DURING MIS 4 AND 3 IN THE TETON RANGE, WYOMING

Extensive MIS 4/3 glacial advances have been recognized in several locations across the western United States, and work of Ken Pierce looms large in the recognition of those pre-Last Glacial Maximum ice advances. Notably, in their landmark study of weathering rind development patterns, Colman and Pierce (1992) suggested that MIS 4 glaciation affected multiple mountain ranges in the region. Unfortunately, these pre-LGM ice advances have received scant attention, owing to dating difficulties and tight disciplinary focus on the LGM and deglacial events. With widespread application of cosmogenic radionuclide exposure dating and luminescence dating, establishing the geochronology of these pre-LGM advances is now possible, and these advances are increasingly relevant to improved understanding of climatic processes through the last glacial cycle.

We use LiDAR data and knowledge of deglacial timing to calculate fault offset rates on the Teton Fault and estimate range-front glacial landform ages. Using a range-front deglaciation age of 14 ka from Licciardi and Pierce (2008), we determine a fault offset rate of 0.82 m/ka for deglacial landforms occupying several valleys crossing the central fault segment. The higher and older moraines marking the range front are offset 23-49 m. Applying a constant fault offset rate to these older moraines, we estimate moraine ages of 27-60 ka. Direct dating of these moraines is clearly necessary to ascertain the age and relevance of these moraines, but our preliminary age estimates indicate that MIS 4/3 glaciation in the Teton Range was slightly more extensive than MIS 2 glaciation. The setting of the Teton Range at the northeastern end of the Snake River Plain suggests that penetration of moist air masses produced more favorable conditions for glacier growth during MIS 4 and/or 3.