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

We report on an investigation of the Red Dog Loess, a last glacial loess in the White River Badlands (WRB), South Dakota, USA. Widespread exposures of Late Eocene through Oligocene-age White River Group (WRG) sediments are thought by some to be the source for the Peoria Loess in southern Nebraska.

At the loess type locality at Red Dog Table, we collected samples at 1 m intervals from the 23 m thick vertical section. We analyzed sediment samples for geochemistry, mineralogy, particle size distribution, and optically stimulated luminescence (OSL). Fossil snails and a paleosol near the top of the section were analyzed for 14C and stable isotopes. Geochemical comparisons for provenance included comparisons of K/Ba and K/Rb. OSL ages ranged from 5 ka near the top of the section to > 58 ka at the base. Radiocarbon results from the upper paleosol gave a calibrated age of approximately 13 ka; the age, character and stratigraphic position of the paleosol suggests it correlates with the Brady Geosol, which separates the younger Bignell Loess from the Peoria Loess (or Red Dog Loess) below. Calibrated ages from amphibious-type gastropod shells (Galba sp.: 2 to 10 mm long) from near the base of the section (18 to 19 m depth) were approximately 23 to 24 ka. Ratios of K/Ba and K/Rb ranged from 21 to 30 and 189 to 254, respectively.

Combined geochemical compositions, OSL, and 14C ages correlate temporally and compositionally with Peoria Loess in the Loess Hills of southern Nebraska, which supports the hypothesis that the WRB was the sediment source. Paleoenvironmental interpretations based on the Red Dog Table sequence are as follows: 1) Sometime before the last glaciation, a floodplain developed on the eroded surface of the WRG strata. 2) Regional incision formed terraces throughout the WRB. 3) a paleosol formed during a period of nondeposition. 4) Near the beginning of the last glacial maximum, Red Dog Loess began to accumulate on high terraces. Simultaneously, WRB sediment was transported through the Nebraska Sand Hills, resulting in loess accumulation in the Loess Hills of southern Nebraska. 5) Approximately 13 ka, a paleosol developed during a time a reduced loess accumulation. 6) Post-13 ka, an additional 5 m of loess accumulated atop the paleosol. Therefore, the loess sequence at RDT the study site appears equivalent to the Peoria Loess-Brady Soil-Bignell Loess sequence found in other parts of the Great Plains.