COSMOGENIC 10BE DATING OF LATE PLEISTOCENE LANDFORMS ALONG THE EASTERN TETON RANGE FRONT: INITIAL CLIMATIC AND TECTONIC INTERPRETATIONS

In northwestern Wyoming’s Teton Range, the last glacial-interglacial transition was characterized by dramatic changes in climate and Teton fault activity; the region therefore provides an excellent natural laboratory to assess the relative roles of climate and tectonics in driving alpine landscape evolution. Here, we present in situ cosmogenic ¹⁰Be measurements from fault-offset surficial deposits in the eastern Teton Range, including an alluvial fan (the Lupine Meadows fan) and a slide (the String Lake slide). We also calculate open-ended Teton fault slip rates for these features using a Monte Carlo approach. For the Lupine Meadows fan, we have obtained ¹⁰Be surface exposure ages from a water-scoured bedrock surface above the fan and from two large boulders embedded in the fan surface. We interpret the ¹⁰Be age from water-scoured bedrock (15.6 ± 0.3 ka) as the closest constraint on the timing of fan abandonment. We calculate a vertical slip rate of 1.3 ± 0.1 m ka^-1 for this feature. ¹⁰Be ages (n=3) from boulders on the String Lake slide surface average 15.4 ± 0.4 ka (excluding one young outlier), and the open-ended vertical slip rate at this site is 1.7 ± 0.1 m ka^-1. From the ¹⁰Be ages and slip rate calculations so far, we make two initial interpretations. First, the end of aggradation on the Lupine Meadows fan and the deposition of the String Lake slide align with the timing of alpine glacier recession from Pinedale terminal moraine complexes in the eastern Teton Range at ~15 ka. We are exploring potential relationships between these events and regional paleoclimate trends. Second, there appears to be an along-strike variation in Teton Fault slip rates since ~15 ka, with the fastest slip rates occurring in the center of the range. Taken together, these results further our understanding of climatic and tectonic controls on the evolution of Pleistocene landscapes.