An Update on the Geochemical Composition of Peninsular India Rivers Average Clay (PIRAC): A Regional Reference for River Sediments of Peninsular India

The rivers draining Peninsular India are rain-fed and their sediments are formed from weathering and erosion of continental rocks in the drainage basins. Peninsular India comprises dominantly the Archean–Proterozoic Terrain (APT) in the south, Deccan Trap Volcanic Terrain (DVT) in the middle, and Mixed-Lithology Terrain (MLT) in the north. Here, we highlight the differences in the average chemical composition of the clay fraction of sediments in rivers that drain dominantly similar geological terrains along the east and west coasts of India, update the geochemical composition of the Peninsular India Rivers Average Clay (PIRAC) based on the sediments from 104 rivers, and suggest that the composition of PIRAC serves as a regional reference for river sediments of Peninsular India. We found that the major elements in the clay fraction of sediments in the rivers are variably affected by the intensity of weathering. On an average, the clays from the east coast rivers showed higher Si, Ti, Fe, Mg, Mn and Na and lower Ca and P than those of the west coast. PIRAC showed more depleted Si, Mg, Ca, Na and K and enriched Ti, Fe, Mn and P relative to the Post-Archean average Australian Shale (PAAS). The clays were extremely weathered in southern Peninsular India, and strong to moderately weathered in central and northern Peninsular India. The average total trace element content (∑TE) of the clays was much higher for the east coast rivers than that of the west coast. The ∑TE of PIRAC was lower than in PAAS. The PAAS-normalised trace elements of PIRAC showed high transition trace elements, low high-field strength elements and large-ion lithophile elements. The average rare earth element content (∑REE) of the clays increased from APT to MLT for the east coast rivers but decreased in the west coast rivers. The ∑REE was lower for PIRAC than in PAAS. The PAAS-normalised REE of PIRAC showed MREE- and HREE-enriched and LREE-depleted pattern, with positive Ce and Eu anomalies. PIRAC is significantly enriched with mafic component dominated material despite Archean–Proterozoic rocks being abundantly widespread in Peninsular India. The intensity of chemical weathering, erosion and transportation of easily eroded mafic rocks relative to that of felsic rocks resulted in deposition of mafic component-dominated material at the lower reaches of almost all rivers. The composition of PIRAC is significantly different from other reference sediments. We suggest PIRAC serves as regional reference for river sediments of Peninsular India.