Clay Mineralogy of the Siwalik Group of Simla Hills, Northwestern Himalaya

Clay mineralogy of the Siwalik Group of Simla Hills was worked out by X-ray diffraction technique. The mineral assemblage comprises kaolinite, illite, chlorite, vermiculite, montmorillonite and mixed-layers. The source rocks bearing feldspars, micas and ferrornagnesian minerals suffered chemical decomposition and mechanical fragmentation in temperate climate. The sediments were deposited in rapidly subsiding fresh-water basins. Terrestrial and (or diagenetic origin has been assigned to the various clay minerals.