Clay mineralogy of the late pleistocene red sediments of the Visakhapatnam region,east coast of India

The fine-fraction mineralogy of the red sediments and of the upland soils along the Visakhapatnam—Bhimunipatnam coastal region has been studied by X-ray analysis. Dominant kaolinite with subordinate illite is the general clay-mineral assemblage in both the red sediments and the soils. The similar clay-mineral composition indicates that the upland soils are the source for the clay material in the red sediments. Montmorillonite is present in some samples and shows greater abundance in the red sediments than in the soils. The additional montmorillonite is considered to have been formed by post-depositional diagenesis in the red sediments at the expense of illite. Differences in the intensity of the weathering process controlled by the gradient in the source area have been suggested as being responsible for the variation in type and abundance of the clay minerals in the red sediments. It is inferred that humid and tropical to subtropical climatic conditions prevailed and persisted throughout the Late Pleistocene and Holocene in the Visakhapatnam region.