301-5 Luminescence dating of Columbian mammoth remains, Ashepoo River, South Carolina

Session: Geochronology (Posters)

Presenting Author:

Authors:

Abstract:

Columbian mammoth (Mammuthus columbi) remains have been identified and excavated from the Ashepoo River channel in Colleton County, South Carolina. The articulated fossils, excavated by the South Carolina State Museum, were in good context, exposed in situ by river channel scour. A dive team collected four samples for luminescence dating in light-proof tubes from sedimentary units in proximity to the mammoth femur. It was hypothesized that the samples would be close in age, deposited shortly after the death of the mammoth, and so act a set of replicate or near-replicate samples targeting the time of burial.  Optically stimulated luminescence measurements were made on HF-etched quartz grains with diameter 180-212 µm. Equivalent dose (D_E) estimates were determined using a single aliquot, regenerative (SAR) method, applying both central age model (CAM) and minimum age model (MAM) calculations. The measured quartz was well-behaved and responsive enough for estimating equivalent doses. Out of 24 small aliquots attempted, all samples included at least 20 aliquots that proved suitable for D_E determinations. These samples produce a nicely consistent data set, with similar ages across varying dose rates. Considering the four samples as replicates, we calculate a mean age based on combining the four estimates. This yields a CAM age of 81 ± 7 ka (MIS stage 5a or 5b), and a MAM age of 63 ± 6 ka (MIS stage 4).  We consider the MAM age estimate (63 ± 6 ka) to be the most likely age of the sediment surrounding the mammoth remains, while the CAM age is likely an overestimate, affected by incompletely bleached grains. MAM estimates correspond well with the strong mode of equivalent dose estimates present at the young end of D_E distribution plots. In contrast, the CAM D_E lies between modes and is represented by fewer aliquot DE values.  The preferred estimate of 63 ± 6 ka places the deposition of sediment surrounding the mammoth remains within MIS-4, a glacial stadial. Future dating work targeting overlying and underlying stratigraphic units in a vertical sequence could potentially provide additional context for the stratum containing the mammoth remains and help in evaluating interpretations leading to the present age estimate. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10009

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