Luminescence Data for the Mammoth Site, Black Hills, South Dakota 2016-19

The ~21 m deep Mammoth Site (MS) bone bed site at Hot Springs, South Dakota, provides a unique opportunity to reconstruct paleoenvironmental conditions on the northern Great Plains of the United States. Past published radiocarbon analyses of mammoth bones found within the MS sinkhole suggested they were deposited ~23-42 ka. However, two U-series ages ranging between 129-150 ka and a thermoluminescence (TL) age of 101 ± 10 ka suggested the bones were considerably older. We analyzed six samples from the bone bed using optically stimulated luminescence (OSL) dating; the ages ranged from ~130-255 ka, showing greater consistency with previous U-series and TL analyses. The OSL dating was on fine sand sized potassium feldspars in the middle “Phase II” section while the deeper colluvial gravels of the sinkhole bottom await renewed borehole drilling for a more complete analysis of the sedimentation record. In addition, we dated a late Pleistocene paludal proxy site using luminescence, incorporated those results with previous radiocarbon dating, and tested bleaching rates on modern sediments in the Fall River. Our new OSL ages also show that the sediments of the MS were well bleached prior to deposition, were derived from pond margin runoff events, and deposited as sandy-silt laminae couplets. The OSL and U-series ages indicate that a 6 m thick section of bone-bearing sinkhole sediments accumulated at a rate of 13 mm/yr and span all of Marine Isotope Stage (MIS) 6 and MIS 7 but not MIS 2 and 3 as has been previously published.