. At the same time, back-mangrove and non-mangrove taxa were very low, indicating a continuous inflow of saline waters to the wetland. The variations in the sedimentation rate, sand fraction, and volumetric mean diameter demonstrated a tidal inundation fluctuation. Between c. 3750 and c. 2950cal y BP, the mangrove pollen accumulation rate was significantly lower compared with the period from c. 2950 to 1850cal y BP indicating that the mangrove pollen were possibly transported to the site. The lowering in RSL gradually shrunk the lagoon after c. 2950 cal y BP. Regression in the Sam Roi Yot area was slightly earlier than that obtained by the beach ridge study and the coastal dune formation at Chumphon.