Mineralogy and, Major and Trace Elements Chemistry of Recent Sediments in Rivers Along the West Coast of India: Implications for Provenance and Chemical Weathering

The sediments deposited at the lower reaches of 90 medium and minor rivers from 5 states along western India were analysed for mineralogy and, major and trace elements chemistry. Kaolinite followed by minor illite and gibbsite and traces of goethite and, smectite followed by minor kaolinite, illite and chlorite are characteristic of the clays from Archean-Proterozoic (A-P) terrain and Deccan Trap (DT) terrain, respectively. The sediments were depleted with Si, Ca, Mg, Na and K relative to that of Post Archean average Australian Shale. The SiO2/Al2O3 ratio suggests the sediments from A-P terrain resemble lateritic soils, while those from DT terrain are non-lateritic, chemically weathered soils. The weathering indices indicate intensely weathered and compositionally mature sediments from Kerala, Karnataka and Maharashtra and, intermediate to intensely weathered sediments from Goa and Gujarat. The sediments exhibit relatively high Th, U, La, Zr and Hf from A-P terrain and, high Sc, Cr, Co, Ni, V and Ga from DT terrain. The total trace element content (∑TE) was lower for the clay than silt fractions of sediments. The peak high ∑TE occur in the silt fraction of sediments from Kerala and Maharashtra. The Th/U and Rb/Sr ratios are controlled by the intensity of weathering and lithology of source rocks. The standard plots using trace elements reveal intermediate provenance between felsic and mafic source. Clay fractions from both terrains are more mafic implying mafic-component dominated sediments are transported to the adjacent Seas and Oceans. Therefore, it would be challenging to identify the clays transported from granitic terrain in the Oceans, using trace element chemistry.