Intertidal and freshwater biota have been recovered from four dated estuarine sediment sections, at Calcutta (CV type section), Dum Dum (DI), Barrackpore (BI) and Kolaghat (KI) in the Bengal Basin, India. Five regional palyno-plankton assemblage zones have been established, from four pollen diagrams. These zones are: 1. (I) Heritiera-Bruguiera-Acrostichum aureum-Fern-Ammonia, 2. (II) Avicennia- Sonneratia-Rhizophora-Ceriops-Bruguiera-Fern-Palaeocirrenalia-Ammonia, 3. (III) Ceriops-Bruguiera-Excoecaria-Avicennia-Sonneratia-Heritiera-Typha-Fern-Concentricystes rubinus (Type I), 4. (IV) Heritiera-Bruguiera-Cheno-Amaranthus-Poaceae-Typha-Fern-Concentricystes rubinus (Type I), 5. (V) Potamogeton-Heritiera-Typha-Poaceae-Fern-Gloeotrichia-Concentricystes rubinus (Type). Six environmental phases of deposition are revealed from the regional palyno-plankton assemblage zones. These are: 1. (1) Upland, arid phase characterised by "Kankar" nodule formation. 2. (2) Mixed brackish water and freshwater environment and inundation by seawater (Ammonia transgression) from 7000 to 6500 years B.P. 3. (3) Mangrove swamp with regular inundation (6500 to 6400 years B.P.). 4. (4) Mangrove tidal flat with high precipitation (6400 to 6175 years B.P.). 5. (5) Mixed brackish water/freshwater Heritiera forest and colonisation by non-littoral species (6175 to 5000 years B.P.). 6. (6) Supratidal freshwater swamp from 5000 to 2000 years B.P. and continuing until the present. The significant environmental succession,revealed through the palyno-plankton assemblage zones between 7000 to 2000 years B.P., indicated transgression of the sea between 7000 and 6175 years B.P., causing landward followed by seaward extension of the mangrove ecosystem in the depositional area. © 1990.