Single-Grain Luminescence Dating of Sediment Surrounding a Possible Late Pleistocene Artifact from the Wenas Creek Mammoth Site, Pacific Northwest, USA

摘要

Excavations at the Wenas Creek Mammoth Site yielded mammoth, bison, and two possible artifacts in a single colluvial stratum, with radiocarbon bone dates ～17 ka. Eight infrared-stimulated luminescence (IRSL) samples were collected to establish general ages of site strata, returning multi-grain estimates consistent with stratigraphic integrity and the radiocarbon dates. Four additional IRSL samples were collected to estimate the depositional age of one artifact found in place. These produced a pooled total of 94 single-grain estimates from near the artifact, 80% averaging 16.8 ± 0.9 ka, and 20% averaging 5.1 ± 0.5 ka. These results could be interpreted to demonstrate pre-Clovis age artifact deposition consistent with the bone dates, or a mid to late Holocene intrusion into older deposits, possibly by bioturbation. The single-grain IRSL dates do not provide proof of pre-Clovis presence beyond reasonable doubt at this site, but do show that this technique is valuable in assessing the stratigraphic integrity needed for any such claim.