Late-Holocene estuarine evolution influencing archeological wooden-pile sites, Bach Dang Estuary, Northern Vietnam

This study integrates geoarchaeological, sedimentological, chronological, and geomorphic evidence to determine the age and environmental context of the wooden-pile sites at Cao Quy and Dam Thuong, and to reconstruct Late-Holocene environmental change in the tide-dominated Bach Dang Estuary, northern Vietnam. Eight AMS radiocarbon ages cluster tightly between ~2515 and 2301 cal BP (~566–352 BCE), indicating that the piles represent late Dong Son stilt-house foundations rather than 13th-century battlefield stakes. Analysis of 29 sediment cores, combined with geodetic surveys of two paleo-sea level notches (+4.0 m and +2.3 m MSL), defines a five-stage environmental evolution from a Mid-Holocene marine embayment to the modern tidal plain. During ~2.7–2.2 ka cal BP, relative sea level estimated at ~1–2 m above present MSL and emergent paleo-highs on the Vinh Phuc surface created a short-lived window for settlement. Stratigraphic evidence shows that this stable phase ended abruptly after ~2.2 ka cal BP, when rapid inundation buried the sites beneath fine, anoxic estuarine muds. This short-lived flooding phase is interpreted to reflect enhanced tidal influence within a progressively infilling estuary, potentially associated with barrier or land-bridge development. The results provide a high-resolution framework linking stepwise sea-level history, estuarine dynamics, and human adaptation, illustrating how short-term hydro-morphodynamic variability shaped both settlement abandonment and exceptional archeological preservation along the northeastern margin of the Red River Delta.