Arroyo Cycles in the Upper Escalante River Drainage, S. Utah: Utilizing OSL to Extend Regional Fluvial Chronologies

Arroyos in the southwestern U.S. have been studied over the past century because of the well-documented period of arroyo cutting in the late 1800s and early 1900s. However, arroyo response to climate change is still not well understood. Many geomorphic studies indicate that minor climate shifts can cause major perturbations to streams in the southwestern U.S. (e.g. Ely 1997; Hereford 2002; Vivoni et al, 2009). Given climate model predictions for the SW U.S. of greater temperature extremes and more frequent floods and droughts, research involving these dynamic fluvial systems is extremely important. The headwaters of the Escalante River in S. Utah provide an excellent setting to examine the timing of arroyo cycles in relation to climate change. Recent improvements in dating techniques (AMS 14C and optically stimulated luminescence (OSL) dating) provide an opportunity to test hypotheses regarding causes of arroyo cutting with greater precision than previously possible. Previous arroyo chronologies are based on 14C dates, although these dates can be problematic due to reworking. Further, charcoal may not be suitably located in a deposit to best constrain the timing of aggradation and degradation, limiting resolution of the record. OSL samples can be collected from any unit containing quartz sand, allowing better chronologic constraints. However, OSL ages may have problems with partial bleaching in fluvial settings. For this reason, a sampling strategy using both 14C and OSL dating is being utilized in the Escalante headwaters