Clay mineral distributions in the continental shelf sediments between the Ganges mouths and Madras, east coast of India

Clay minerals have been determined in samples of shelf sediments along the east coast of India between the Mahanadi River in the north and Madras in the south. The data have been collated with published clay mineralogy of the east coast shelf sediments, and fluvial and estuarine sediments of the adjacent rivers to evaluate the clay mineral distribution patterns in the shelf visávis clay mineral provenance. Trends in the relative proportions of the clay minerals define three major clay mineral provinces along the shelf from north to south: the Himalayan, Eastern Ghats and Deccan Provinces. The Himalayan Province is characterized by abundant illite followed by chlorite, and the Deccan Province by abundant smectite from the Deccan basalts. The Eastern Ghats Province is mixed, the northern region being dominated by illite and kaolinite and the southern region by smectite and illite. The Eastern Ghats Province is not represented in the clay assemblages from the deep Bay of Bengal, while the other two are. Chlorite is virtually absent in the fluvial sediments of the Peninsular rivers and its presence in the adjacent shelf sediments is attributed to three sources: (a) southerly transport of chlorite-rich Ganges sediments over the shelf in suspension, (b) advection of the Ganges-derived suspended solids from east to west across the Bay of Bengal, and (c) reworking of Pleistocene and early Holocene sediments in the shelf. The present study suggests that the clay mineralogy of the distal Bengal Fan is controlled by the relative rates of sediment supply from Himalayan and Deccan sources. The chlorite-rich sediments in the distal fan are derived primarily from the former source and the smectite-rich sediments primarily from the latter source.