EROSION RATES AND TIMING OF LATE HOLOCENE PEDIMENT DISSECTION IN THE WHITE RIVER BADLANDS, SD

Sod tables across the White River Badlands of South Dakota are remnants of Holocene pediments that have been incised by streams. During periods of lanform stability, soil forms on the pediments, while subsequent alluvial-colluvial deposition results in burial of the soil, hence formation of a paleosol. Incision of the pediment separates the sod table from the surrounding highlands and precludes further alluvial deposition. Hence, the uppermost paleosol constrains the maximum age for the onset of incision. The dimensions of the resulting gullies can be combined with the timing of incision to calculate erosion rates for vertical incision and channel widening (lateral retreat of banks) of the washes surrounding sod tables. Gullies were surveyed three to five times to gain confidence in the erosion rates reported.

We report here paleosol radiocarbon ages and erosion rates for two localities on the lower prairie of the Badlands, within Buffalo Gap National Grassland, along Highway 44 between Scenic and Interior, SD. The uppermost paleosol age sampled from a table at Imlay was 670 + 70 RCYBP and that from the western flank of Bouquet Table was 1610 + 70 RCYBP. For Imlay lateral retreat ranges between 2-4 cm/yr and vertical incision ranges between 0.1-0.3 cm/yr and for Bouquet Table lateral retreat ranges between 0.7-1.3 cm/yr and vertical incision ranges between 0.17-0.23 cm/yr.

The rates for Imlay and Bouquet Table reveal rapid erosion. We believe aridity associated with the Medieval Climate Anomaly triggered the incision of these pediments and formation of the sod tables. We are working to understand how gully development proceeded across the region in response to this climate change. We are also examining parabolic dunes fields in the vicinity to assess the role of climate in forcing synchronous perturbation of both slopes and eolian deposits.