RED DOG LOESS, A PEORIA EQUIVALENT, LAST GLACIAL LOESS OF THE WHITE RIVER BADLANDS, SOUTH DAKOTA, USA

This presentation reports on an ongoing investigation of the Red Dog Loess, a last glacial loess in the White River Badlands (WRB), South Dakota, USA. The WRB landscape is dominated by the effects of erosion and mass wasting but includes Quaternary deposits of aeolian sand and silt. Previous work established an OSL chronology of three dune forming episodes at 1) ∼21 ka to 12 ka, 2) ∼9 to 6 ka, and 3) post-0.7 ka. The age of the Red Dog Loess remains poorly constrained, but likely this loess is a composite of similar age to the Peoria Loess-Brady Soil-Bignell Loess sequence of the central Great Plains.

The Red Dog Loess type locality is Red Dog Table, located in the extreme southwestern section of the WRB. Red Dog Table, a mesa approximately 1 km², is one of many mesas and buttes in the western WRB with loess exposures up to 30 m thick. When the Red Dog Loess name was proposed in 1968, it was assumed to be equivalent to the Peoria Loess. Since the name was accepted, the Red Dog Loess has received little attention from investigators, likely because of the remoteness of the best exposures.

The 23 m thick type section of the Red Dog Loess is located at the NE edge of the mesa in a nearly vertical exposure. The section is deposited unconformably on the Oligocene upper Brule Fm. The Quaternary deposit from bottom to top consists of a) 10 m of prismatic, vertically jointed and moderately indurated loess, b) 6 m of massive, poorly indurated loess, c) 1 m of loess paleosol, and d) 6 m of massive, poorly indurated clifftop loess. A single radiocarbon sample from the paleosol gave an age of approximately 13 ka, within the period of the Brady Soil formation (~15 ka to 10.5 ka).

In summer 2022, we collected samples from the Red Dog Loess type section at 1 m intervals for geochemical, mineralogical, and particle size analysis, and we collected OSL samples at three-meter intervals. For comparison, we collected additional samples from a second, downwind section at Red Dog Table. Summer 2023 the team returned to collect high-resolution drone imagery of the mesa for geomorphological analysis. This presentation will summarize OSL and other results of this investigation, interpret the age and environment of deposition of this formation, and put the Red Dog Loess in the context of other loess deposits on the Great Plains.