EVALUATION OF APATITE AGE DISTRIBUTIONS BETWEEN GRAVEL AND SAND SEDIMENTS IN GLACIAL AND FLUVIAL DEPOSITS

Mineral ages in sedimentary deposits are used to understand erosion patterns and mountain uplift. In a small catchment we assume all sediments, regardless of size, reveal the same patterns. This research investigates the apatite age distributions of sand and gravel located in stream and moraine deposits in two canyons in the Teton Mountains: Garnet and Cascade. Stream samples from active channels near the mouth of each canyon and moraine samples close to the shores of Bradley and Jenny Lakes were collected and processed at Illinois State University. Gravel samples were crushed, and all samples were washed, sieved, and run through heavy liquids and the Frantz magnetic separator to isolate apatite grains. Samples were then picked to measure He content with mass spectrometry and U-Th with laser ICP-MS. A previous study by Tranel et al. (2011) tested and compared two samples of sand, one found in a Garnet Canyon stream, and the other found in glacial deposits of the Bradley Lake moraine at the mouth of the canyon. This previous study concluded that the sand sediments found in the stream were on average 39ma while the sample from the moraine were on average 42ma. The stream samples ranged from 10ma to 75ma. The moraine sample ranged from 5ma to 80ma. We expect similar apatite ages in the larger and more complex Cascade Canyon. New results from Garnet and Cascade Canyons will determine if the ages in sand and gravel samples are influenced by the size of the sediment collected. Observations of many fractured grains in glacial sediments suggest transport processes may influence the range of ages in our results. The results of this study will help plan effective sampling strategies in future studies investigating erosional patterns in mountain landscapes.