Clay mineral distribution in the shelf sediments off the Northern part of the East coast of India

Forty-eight sediment samples from the continental shelf between Visakhapatnam and the Ganges were analysed by X-ray diffraction for the composition and distribution of clay minerals. Estuarine samples of the Hooghly are dominated by illite and chlorite with minor amounts of kaolinite and traces of montmorilionite. In the shelf sediments, the illite and chlorite concentrations decrease with increases in the concentrations of montmorillonite, kaolinite and gibbsite. The Ganges-derived sediment does not reach the shelf off the peninsular rivers. Sediment samples off the peninsular rivers show illite, kaolinite and montmorillonite with minor amounts of chlorite and gibbsite. Spatial variations in the distribution of clay minerals indicate that illite and kaolinite concentrations are higher in the clay fraction of the more sandy sediments and montmorillonite proportions are higher in the clays. The clay minerals present in the shelf sediments closely reflect their sources but their relative abundance depends largely on the energy conditions of the shelf environment and the properties of the individual clay minerals