A 12.8 ka microspherule and nanoparticle marker horizon in stratified Paleoamerican deposits at Smith Mountain Lake (44PY152), USA

Geoarchaeological investigations at site 44PY152 near Smith Mountain Lake, Virginia, document stratified Late Pleistocene–Early Holocene archaeological occupations preserved within ~1.7 m of floodplain alluvium. These deposits contain both in situ and eroding fluted Paleoamerican and Early Archaic projectile points. Here, we analyze a contiguous, high-resolution sedimentary sequence to evaluate the presence and stratigraphic integrity of microspherule and platinum-group element (PGE) anomalies associated with the onset of the Younger Dryas (YD). Analyses include Bayesian radiocarbon modeling, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS), laser ablation ICP-MS (LA-ICP-MS), laser granulometry, bulk organic carbon and nitrogen, soot carbon, stable carbon isotopes (δ¹³C_OC and δ¹³C_soot), magnetic susceptibility, and mercury (Hg). Results reveal a narrow microspherule-rich interval centered within the 14–15 cmbd sample that is accompanied by pronounced PGE mass anomalies consistent with proxy assemblages reported near the Younger Dryas Boundary at multiple sites worldwide. Bayesian age modeling places this interval within the broader temporal range of the Younger Dryas onset, although the modeled age uncertainty exceeds the narrower age range proposed by Kennett et al. Chondrite-normalized elemental systematics indicate selective Pt-centered enrichment decoupled from comparatively conservative rare earth element behavior, arguing against simple sedimentological concentration processes. The stratigraphic position and internal coherence of this proxy suite identify a discrete marker horizon consistent with the onset of the Younger Dryas at 44PY152. Subtle excursions in δ¹³C_soot and Hg immediately above this interval may reflect associated environmental variability during the early Younger Dryas. Regardless of formation mechanism, the microspherule–PGE horizon provides a high-resolution stratigraphic marker confined to a 1-cm interval that may aid correlation and interpretation of pre- and post-12.8 ka archaeological sequences at stratified sites lacking abundant chronometric control.

Source: ScienceOpen - ScienceOpen Research PDF: https://doi.org/10.14293/s2199-1006.1.sor.2026.0003.v1 Original Link: https://doi.org/10.14293/s2199-1006.1.sor.2026.0003.v1