Distribution and dispersal of clay minerals on the western continental shelf of India

Abstract

Sediment samples distributed over a distance of 1700 km from the inner continental shelf of western India were analysed for their clay-mineral content by X-ray diffraction. The clay minerals present in the sediments, in order of abundance, are montmorillonite, kaolinite, illite, chlorite and gibbsite. Based on the abundance of montmorillonite and kaolinite, four clay-mineral provinces on the continental shelf have been demarcated. These are: (1) the montmorillonite-kaolinite-illite-chlorite province off the Gulf of Kutch; (2) the montmorillonite-rich zone off the Gulf of Cambay; (3) a transition zone on the central parts of the shelf; and (4) a relatively montmorillonite poor-gibbsite province on the southwestern part of the shelf. Source-rock influence on clay-mineral composition appears to be more important than physical transport — the southwest monsoon drift in the present case. In the northwestern part of the study area, the high-velocity tidal streams of the macrotidal Gulf of Kutch act as dynamic barriers to longshore sediment dispersal, leading to distinct clay-mineral assemblages on the shelf north and south of the gulf mouth.