Beryllium-10 surface exposure dating of glacial successions in the Central Alaska Range

Glacial landforms and outwash terraces in the Nenana River valley, Reindeer Hills and Monahan Flat in the central Alaska Range were dated with 60 ¹⁰Be exposure ages to determine the timing of Late Pleistocene glaciation. In the Nenana River valley, glaciation occurred at 104-180-ka (Lignite Creek glaciation), ca. 55-ka (Healy glaciation), and ca. 16-ka (Carlo Creek phase); glaciers retreated in the Reindeer Hills and Monahan Flat by ca. 14-ka and ca. 13-ka, respectively. The Carlo Creek moraine is similar in age to at least six other moraines in the Alaska Range, Ahklun Mountains and Brooks Range. The new data suggest that post-depositional geological processes limit the usefulness of ¹⁰Be methods to the latter part (≤60-ka) of the late Quaternary in central Alaska. Ages on Healy and younger landforms cluster well, with the exception of Riley Creek moraines and Monahan Flat-west sites, where boulders were likely affected by post-depositional processes.