Characteristics of Diatom and Pollen Assemblages and Their Significance at the Nhon Thanh Archaeological Site, Can Tho City, Southern Vietnam

NGUYỄN Thị Thu Cúc1*, FUNABIKI Ayako2, NGUYỄN Hoàng Bách Linh3, and NGUYỄN Thị Mai Hương4

This study reconstructs late Holocene paleoenvironmental change at the Nhon Thanh archaeological site, Can Tho City, southern Vietnam, using pollen and diatom analyses. Twelve pollen and ten diatom samples were recovered from a sediment core (−325 to +40 cm elevation). Four radiocarbon dates span ca. 3100 cal BC to 400 cal AD. Fifty-one diatom taxa were identified, representing marine, brackish, coastal, and freshwater assemblages. Stratigraphy delineates three diatom ecozones (NT1–NT3), reflecting a progressive transition from marine–brackish to freshwater conditions. Pollen data parallel this pattern: lower horizons are dominated by mangrove and brackish taxa (Rhizophora sp., Sonneratia sp., Barringtonia sp., Acrostichum sp.), while freshwater herbs increase upward, yielding Zones 1–3. The oldest date (3104–2922 cal BC) at 0.82–0.72 m a.s.l. aligns with pollen Zone 2 and diatom NT2, indicating reduced sea temperature and salinity relative to deeper marine deposits. Stratified cultural deposits are divided into three phases spanning the centuries BC to the mid-7th century AD, corresponding to pollen Zone 3 and diatom NT3 and indicative of a coastal-wetland setting. The site’s elevation lies slightly below the contemporary sea-level curve. An inland beach ridge on the delta lobe formed ~2700 years ago; by the time of occupation its elevation likely curtailed seawater intrusion, facilitating habitation.