Geochemistry and Mineralogy of Peninsular Indian River Sediments with Special Reference to Godavari and Krishna Rivers

The Godavari and Krishna Rivers, which originate in the Deccan Traps and flow through a variety of geological formations before emptying their sedimentary burden into the Bay of Bengal (BoB), are two of Peninsular India’s most significant rivers. Sediments from the Godavari and Krishna Rivers, major, minor, and trace elements geochemistry show signs of sedimentary sorting during transportation and deposition. The primary source of the bed sediments in the upper portions (upstream) of these rivers is the weathering of basaltic rocks from the Deccan volcanic province. In contrast, the weathering of old felsic rocks, which have a vastly different chemical and mineralogical makeup, is the main source of sediments in lower reaches (downstream). The very elevated strontium and neodymium isotope ratios in downstream sediments (87Sr/86Sr and 143Nd/144Nd) indicate a large contribution from weathering of felsic minerals. Rare-earth elements (REEs) have manifested distinctive patterns that reflect the mineralogy of their source rocks. When subjected to weathering, transit, and depositional processes, the light rare-earth elements (LREEs) often exhibit more fractionation than the heavy rare-earth elements (HREEs). In the higher reaches of the Godavari and Krishna basins, the chemical index of alteration (CIA) varies greatly, indicating significant regional heterogeneity in the degree of chemical weathering. On the other hand, downstream sediments with relatively high CIA values have shown parental rocks to have undergone moderate to strong chemical weathering.