Investigations of the spatial and temporal variations of Sr and Nd isotopes in sediments from two Indian Rivers: Implications to source identification

Radiogenic isotopes of Sr and Nd provide crucial information on chemical and physical erosion processes, therefore used as tracers for fingerprinting the sources of fluvial sediments. Moreover, elemental geochemistry, ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd signatures in silicate fractions of sediments primarily reflect intricate controls of characteristics and provenance of sediment. A suite of sediment samples collected from two rivers of India, Narmada (large) and Netravati (small) were analyzed for elemental concentrations, ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd in silicate as well as acid-leachable fractions. ⁸⁷Sr/⁸⁶Sr in acid-leachable sediment fractions from both the rivers (0.7094 ± 0.0002 for Narmada and 0.7158 ± 0.003 for Netravati) showed more radiogenic ⁸⁷Sr/⁸⁶Sr in Netravati compared to Narmada indicating influence of source rocks in their watersheds. Weak correlation of sedimentary ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd with Al and Chemical Index of Alteration (CIA) in silicate fraction indicates that isotopic compositions are primarily controlled by their sources and not by chemical weathering in both the rivers. Provenance of sediments in Narmada is dominated by their supply from Deccan deposits with secondary supply from mid-late Proterozoic Vindhyan along with Mesoproterozoic to Mesoarchean T^Nd_DM ages. Sediments from Netravati reflected signatures of peninsular gneisses dominant with gneisses schists and granodiorite along with Paleoarchean T^Nd_DM ages. Based on variability of ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd, present study highlight that sediment supplies from tributaries to the mainstream in Narmada is inadequate as compared to that in Netravati. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd signatures in Narmada and Netravati are comparable with Global Rivers.