PACE AND TIMING OF LATE PLEISTOCENE ICE RECESSION IN THE TAYLOR VALLEY, SAWATCH AND ELK RANGES, COLORADO, USA

Terrestrial cosmogenic nuclide (TCN) ¹⁰Be exposure dating of glacial features has significantly enhanced understanding of the Taylor River Glacier Complex (TRGC) and its glacial history. The TRGC, encompassing an area of approximately 215 km², was primarily fed by the Taylor River and several significant tributaries, including Bowman, Pine, Tellurium, Italian, and Red Mountain Creek Drainages. At its maximum, the TRGC extended ~22 km down the Taylor River valley, with evidence suggesting a quasi-stable terminal moraine complex around 20,000 to 18,000 years ago. The presence of at least 9 recessional moraines indicates that TRGC retreat was interrupted by multiple standstills or readvances. Previous TCN dating efforts primarily focused on determining the timing of terminal moraine deposition for the TRGC and neighboring valley glaciers. This study presents seventeen new ¹⁰Be exposure ages of erratic boulders from atop five moraine surfaces in the Taylor River valley. These include the terminal moraine and four recessional moraines, representing ice retreats of approximately 10%, 20%, 40%, and 60% from the terminal position. The reported exposure ages derived from these samples provide crucial insights into the timing of glacier retreat within the TRGC, facilitating the continued investigation of climate influences on late Pleistocene glacier recession. Notably, our results indicate a considerable deceleration in TRGC retreat during the Heinrich Stadial 1 (HS1) cooling phase, followed by a period of enhanced retreat near the conclusion of HS1. Additional TCN exposure dating of TRGC recessional moraines will further improve temporal resolution of ice retreat and will help to resolve the complex dynamics that result from the influence of multiple large tributaries.