CLAY MINERAL DISTRIBUTIONS IN THE CONTINENTAL-SHELF SEDIMENTS BETWEENTHE 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 M adras in the south. The data have been collated with published clay mi neralogy of the east coast shelf sediments, and fluvial and estuarine sediments of the adjacent rivers to evaluate the clay mineral distribu tion patterns in the shelf vis ri vis clay mineral provenance. Trends in the relative proportions of the clay minerals define three major cl ay mineral provinces along the shelf from north to south: the Himalaya n, Eastern Ghats and Deccan Provinces. The Himalayan Province is chara cterized by abundant illite followed by chlorite, and the Deccan Provi nce by abundant smectite from the Deccan basalts. The Eastern Chats Pr ovince is mixed, the northern region being dominated by illite and kao linite and the southern region by smectite and illite. The Eastern Gha ts Province is not represented in the clay assemblages from the deep B ay of Bengal, while the other two are. Chlorite is virtually absent in the fluvial sediments of the Peninsular rivers and its presence in th e adjacent shelf sediments is attributed to three sources: (a) souther ly transport of chlorite-rich Ganges sediments over,the shelf in suspe nsion, (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 tha t the clay mineralogy of the distal Bengal Fan is controlled by the re lative 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 l atter source.