Mollusc associations of the Northern Gulf of Thailand and Holocene analogs from the Bangkok Clay

The present paper examines Holocene and Recent molluscan associations (or assemblages) of Thailand and identifies pairs, each including a modern association and its fossil analog. The aim is to reconstruct precisely the environmental meaning of the Holocene associations, assuming that these have dwelled the same environment of their modern counterparts. The Anadara granosa-Cerithidea cingulata assemblage records innermost muddy tidal flat conditions, with mangrove vegetation. The Alveinus ojianus-Nuculana (Scaeoleda) mauritiana association thrived in an outer tidal flat, also muddy, that experienced sedimentary instability in turbid waters. The Nuculana (Jupiteria) puellata-Chrysallida melvilli association occurred in sandy mud, at the transition between intertidal and infralittoral zones, and denotes some scouring and turbulent water. The Timoclea (Chioneryx) scabra-Arcopagia pudica association dwelled upper infralittoral bottoms of sandy mud, hardly exceeding 10 m depth. Finally, based on the relative geographic position of the fossil Nuculana (Jupiteria) puellata-Chrysallida melvilli association and of its modern analog Nuculana (Jupiteria) puellata-Pitar (Costellipitar) manillae association, a progradation rate of the tidal flat of 1.6 m/yr during the last 820 years was calculated.