Detailed geochemical and clay mineralogical investigations were carried out on bed sediments from upper Godavari river of peninsular India. The results suggest that these sediments are mainly derived from weathering of basaltic rocks of Deccan volcanic province. Strong relationship between Fe2O3 and TiO2 is attributed to their co-occurrence in weathering resistant minerals and/or scavenging of Ti by Fe oxy-hydroxides during weathering of basalts. The concentrations of Na2O, K2O and MgO in these upper Godavari river sediments are relatively less compared to parent basalt. The abundance of minor elements like V, Cr, Cu and Zn shows significant scatter within the range of Deccan basalts. Vanadium and nickel shows significant correlation with Fe2O3 due to their association with iron minerals or their sequestration with iron oxy-hydroxides. Higher Zn concentrations at some locations of Godavari river may have been due to anthropogenic contamination. The REE pattern is greatly influenced by the degree of source rock weathering. Light rare earth elements (LREE) show greater fractionation compared to the heavy rare earth elements (HREE) during weathering and transportation. Strong positive Ce-anomaly in some sediment samples suggests oxidizing conditions of deposition. Chemical Index of Alteration (CIA) varies significantly from 37.01 to 60.16, indicating large spatial variability in the intensity of chemical weathering of Deccan basalts. Low CIA values are observed in samples that are enriched in CaO probably due to semi-arid climate which facilitates CaCO3 precipitation and restricts chemical weathering.
The major, trace and rare earth elements geochemistry and clay mineral compositions in the river bed sediments from lower reaches of Godavari river suggest that they are derived from weathering of felsic rocks. Trace and rare earth elemental compositions indicate evidence of sedimentary sorting during transportation and deposition. Lower concentrations of transition elements, such as V, Ni and Cr imply enrichment of felsic minerals in these bed sediments. The REE pattern in lower Godavari sediments is influenced by the degree of source rock weathering. The light rare earth elements (LREE) content are indicating greater fractionation compared to the heavy rare earth elements (HREE). A striking relationship is observed between TiO2 and ΣREE content suggesting a strong control by LREE-enriched titaniferous minerals on REE chemistry. Shale-normalized REE pattern demonstrate a positive Eu anomaly, suggesting weathering of feldspar and their secondary products, which are enriched in Eu. Chondrite-normalised REE pattern is characteristic of felsic volcanic, granites and gnessic source rocks. Trace elemental compositions in sediments located near urban areas suggest influence of anthropogenic activity. Chemical Index of Alteration (CIA) is high (avg. 65.76), suggesting a moderate chemical weathering environment. X-ray diffraction analysis of clay fraction shows predominance of clay minerals that are formed because of the chemical weathering of felsic rocks.
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