Heavy sediment influx during early Holocene: Inference from clay mineral studies in a core from the Western Bay of Bengal

Clay mineral studies were carried out in a 6 50 cm long sediment core collected at a depth of 2200 m from the north-western Bay of Bengal. Illite is the predominant mineral, followed by montmorillonite and chlorite. Illite concentration varies from 49 to 65% from the core top to 380 cm and further down, increases to 85%. Montmorillonite content ranges from 22 to 36% above 380 cm, with a max imum in the upper 20 cm. Lowest values of montmorillonite (3– 8%) are observed below 380 cm. Chlorite values range from 12.8 to 29%. Kaolinite is present in traces. The changes in mineral composition at 380 cm in the core are interpreted to be a transitional period of Plei stocene–Holocene. This is substantiated by the litholog ical, foraminiferal and geochemical studies of the core. Very high content of illite below 380 cm of the core reflects glacial weathering products of crystalline met amorphic/sedimentary rocks of Himalayas carried by Ganges–Brahmaputra rivers during the late Pleistocene, when the sea level was low. Increase of montmori llonite and kaolinite during the Holocene indicates that the Ganges–Brahmaputra province sediments were diluted with sediments from the peninsular rivers drai ning metamorphic gneisses, schists, Deccan Traps and Quaternary sediments. This distribution can be explained by circulation pattern and tectonics in the Ganges delta during early Holocene. The top 380-cm thick sediment deposition during Holocene is attributed to heavy sediment influx du ring Mid Termination (MT) (12,500–10,000 years BP), due to increased precipitation and run-off resulting from high intensity monsoonal regime.