A Note on the Burial Diagenesis of Clay Minerals in the Bengal Fan

A thick (770m) pelitic section ranging in age from Quaternary to Middle Miocene encountered at the DSDP site 218 in the Bengal Fan has been investigated for the burial diagenesis of clay minerals based on x-ray diffractometry and partial chemical analysis. The clay minerals are dominated by illite, with minor amounts of montmorillonite, chlorite and kaolinite. All the clay minerals are descrete and detrital derived from the Himalayan hinterland. The clay mineral transformations are largely confined to compaction attendant on the escape of pore water and adsorption of K and Mg in the interlayer positions resulting in better organised illite, montmorillonite-illite and montmorillonite-chlorite mixed layers at depth. The sediments are considered to be in the early diagenetic stage of Dunoyer de Segonzac (1970).