Geomorphology and sediment character of beach-dune complex along Udaipur, Shankarpur and Junput coasts, West Bengal, India

摘要

The Junput-Shankarpur-Udaipur coastal belt is characterised by rows of aeolian sand dune units like neo dune, older dune and older dune ridge. The neo dune unit (lying on the present day sea front) is under active dune building process. The older dune unit is stabilised and the older dune ridge is matured. In the study area of Junput and Shankarpur coasts, only neo dune and older dune units were delineated. In Udaipur coastal belt, three dune units are demarcated. In Junput and Shankarpur the width of the inter tidal zone is 347 to 514m and 224 to 376m respectively. Inter tidal zone of Udaipur is 237 to 426m. The gently sloping beach of the three coasts is veneered by fine to very fine sands with occasional silt and clay. Remnants of palaeomud are exposed at places on the Udaipur and Shankarpur beach. Clay balls, originating from the clayey mass are scattered in intertidal zone near high water line. The clay balls might have been brought to the coast from the submarine erosion prone zone in the near coastal sea bed. The sediments of Udaipur beach are brought mostly from the adjoining near coastal sea bed which is covered by modern fine sand. The surficial sediments of near coastal seabed, mixed with materials derived from Subarnarekha are mostly sands of erstwhile coast, which is now submerged. Ilmenite, garnet, sillimanite and zircon, present in the sediments in Udaipur sector might have been derived from Subarnarekha River borne sediments as well as by transportation from Orissa offshore along with relicts of quartz grains. Sillimanite and chlorite, present in considerable amount in very fine sands of Junput coast are mostly derived from Hooghly River sediments. Eastern and Western Brace prevent seabed sediments on the inner continental shelf from moving westward of Junput offshore.The brownish tint of quartz grains in older dune and older dune ridge is due to their exposure over a wide span of time, which is partially oxidised. Micro features of quartz grains of these dune units suggest attrition during transportation in aeolian environment.The geomorphic features of this coast belt are the result of fluvio-tidal and marine coastal sediments, formed during different stages of Flandrian transgression at around >5900 years B.P.