TERRESTRIAL IN-SITU COSMOGENIC NUCLIDE DATING OF VENTIFACTS WITH 10BE TO CONSTRAIN THE DEPOSITION OF ALLUVIUM IN ROBERTS PRAIRIE DOG TOWN, BADLANDS NATIONAL PARK

We collected four vein quartz ventifacts from Roberts Prairie Dog Town in Badlands National Park, South Dakota. ¹⁰Be terrestrial in situ cosmogenic nuclide (TCN) dating was used to determine how long the ventifacts have been exposed to galactic cosmic radiation (GCR). The dates for the ventifacts were intended to help constrain the timing of when the alluvium on the upper prairie of the White River Badlands was deposited. The exposure dates are 77±4, 68±3, 58±4 and 122±4ka. We had anticipated late Pleistocene to Holocene dates. Therefore, we believe that the ventifacts display inheritance of TCN nuclides, accumulated after exhumation in the Black Hills and during subsequent erosion and fluvial transport. To correct for inheritance at least four more samples need to be collected from various depths, but not exceeding the penetration depth of GCR. Such a sample location would be selected to safely assure that all of the samples would have the same inheritance. A depth profile of the ¹⁰Be could then indicate the erosion rate, alluvial deposition and, most importantly, a baseline to correct for inheritance.