Abstract
Sediment samples distributed over a distance of 1700 km from the inner continental shelf were analysed for their clay-mineral content by XRD. 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 have been demarcated on the continental shelf: 1) montmorillonite-kaolinite-illite-chlorite province off the Gulf of Kutch; 2) 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 SW part of the shelf. Source-rock influence on clay-mineral composition appears to be more important than physical transport by the SW monsoon drift. In the NW part of the study area, 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. (Authors' abstract)