LATE QUATERNARY (MIS-3 TO MIS-1) STRATIGRAPHIC TRANSITIONS IN A HIGHLAND BERINGIAN LANDSCAPE ALONG THE KUSKOKWIM RIVER, ALASKA

Few Quaternary stratigraphic and paleoenvironmental records in southwestern Alaska predate 30,000 ¹⁴C yrs B.P. In addition, continuous stratigraphic records extending to MIS-3 (58,000 to 25,000 cal. yrs B.P.) in Beringia are extremely sparse due to local glaciations and periglacial processes removing older deposits, and those known exhibit a considerable degree of chronological uncertainty. We present a preliminary study on three stratigraphic sections in southwestern Alaska along the central Kuskokwim River that shows continuous environmental progressions between MIS-3 through MIS-1. This region lies in what was once a highland landscape at the fringe of central and eastern Beringia, and likely served as corridors for colonization of Asiatic biota, and possibly humans, from the Bering Land Bridge to other parts of interior and southern Alaska.

The Kuskokwim, Kolmakof VABM, and Sue Creek sections lie between two of the Kuskokwim River’s tributaries the George and Kolmakof rivers, and each contain loess and soil sequences that date back to 50,000 ¹⁴C yrs B.P. Thick and continuous peat development and shallow lacustrine, flood and tephra deposits represent the MIS-3 interglacial period (ca. 52,000 to 35,000 ¹⁴C yrs B.P.) at these sites. Sand sheet and loess deposits, wedge cast development, and very thin and discontinuous soil development marks the MIS-2 glacial period (<35,000 to 16,000 ¹⁴C yrs B.P.). The MIS-1 (Holocene interglacial) period is represented by loess accumulation with thicker soil development during the period of 16,000 to 11,730 ¹⁴C yrs B.P. After 11,000 ¹⁴C yrs B.P., a waning in loess accumulation, tephra deposition, and increased peat development mark the later sequences of MIS-1. Our stratigraphic study shows the transitions between a warm and moist period during MIS-3, to a cooler and more arid period during MIS-2, followed by a return to warmer and moister climates in MIS-1. These sections provide important paleoenvironmental and paleoclimatic contexts to understanding the movement of biota and humans across Beringia during the Late Quaternary.