REFINING PALEOENVIRONMENTAL CONDITIONS DURING THE PLEISTOCENE–HOLOCENE TRANSITION IN EASTERN BERINGIA USING POST-IR IRSL

Dune deposits are commonplace along the Tanana River and its tributaries in eastern Beringia (central Alaska). The affinity between dunes and early inhabitants is well documented—artifacts and geochronological evidence suggesting human occupation as early as 13 ka. Left unknown is the formation history of these dunes and surrounding sand sheets, in part because typical dating techniques (e.g., radiocarbon, OSL, IRSL) remain problematic for the region. This study employs a post-IR IRSL dating technique, which is used to refine periods of aeolian activity in two regional dune fields: the Wood River and Nenana River dune field. In the Nenana River dune field, luminescence ages indicate initial construction of dunes ~16 ka. Dunes contain visible stratigraphy and are capped with loess that was deposited between 11–10 ka, suggesting that dunes remained stabilized since their formation. Dunes in the Wood River dune field show similar stratigraphy and also formed ~16 ka. Multiple layers of Holocene loess cap the Wood River dunes. This new chronology suggests relatively dry and windy conditions at the end of the Pleistocene, and a landscape void of substantial vegetation. The stabilization of these dune fields by 10 ka supports the argument for increased moisture, and in particular, increased forest vegetation. The number of archeological sites in the region found atop dunes, as well as independent age control on artifacts, suggests that early humans used these sites prior to their final stabilization by forest vegetation, which is also supported by this chronology. Additionally, this new chronology emphasizes the importance of dunes in the search for early archeological records. Considering that dunes in the region were formed almost 4 ka prior to documented human occupation, it is not unreasonable to believe that more and possibly even earlier evidence of human occupation could be found in dune fields of eastern Beringia.