RECENT FINDINGS IN QUATERNARY AEOLIAN CHRONOLOGIES IN THE WHITE RIVER BADLANDS, SOUTH DAKOTA

We continue to refine an integrated chronology of late Quaternary alluvial and aeolian events that affected landscape development in the White River Badlands (WRB) of South Dakota. The WRB is located in southwestern South Dakota, 60 km upwind of the western Nebraska Sand Hills. Regional and global fluctuations in paleoclimate created a landscape dominated by alluvial and fluvial incision, which, nonetheless, included periods of aeolian sand and loess deposition. Previous results determined 1) an OSL-based chronology of aeolian activity and 2) a 14C-based chronology of latest fluvial incision of alluvial paleosols. These results indicate periods of dune activity similar to the Nebraska Sand Hills (NSH) and incision of alluvial fans approximately coincident with the Medieval Climate Anomaly (MCA).

Integration of the WRB aeolian and alluvial chronologies was improved by observations in summer 2021 field season that determined cross-cutting relationships between upland dissected mesas and lowland dissected alluvial deposits (sod tables). New observations together with previous results indicate 1) loess deposits of as much as 30 m thickness (Red Dog Loess) on upland table surfaces are late Pleistocene through the latest Holocene. Red Dog Loess ages were based on OSL ages (18.4 to 12.7 ka) and Pleistocene mammal fossils observed at the base of the sequence. 2) Sod table incision occurred in the latest Holocene, approximately coincident with the MCA. Alluvial deposits in the sod tables incorporate reworked aeolian sand and loess from upland table surfaces. 3) The loess mantling the sod tables is likely windblown, rather than reworked material, and was deposited post-incision in the latest Holocene.

It remains to be determined whether Red Dog Loess is the northern Great Plains equivalent of the Peoria Loess, but ages indicate the Red Dog Loess (18 to 12 ka) overlaps the middle to latest deposition of the Peoria Loess (25 to 13 ka). Further, timing of incision of the upland tables, which produced 60 m of relief, may have begun in the early stages of Red Dog Loess deposition. Results from 14C analysis of paleosols from the Red Dog Loess and the sod tables, collected this summer, will add absolute ages to further refine this chronology.