Climate induced temporal change in Sr-Nd isotope ratios in the valley-fill deposits of the Ganga river

Abstract

The ⁸⁷Sr/⁸⁶Sr values in carbonate nodules and ⁸⁷Sr/⁸⁶Sr and εNd values in silicate samples from the valley-fill deposits of the Ganga river have been used to ascertain temporal changes in sediment provenance during the last glacial-interglacial cycle. To understand the changes, a 25 m long core named as the Firozpur core has been sampled for carbonate nodules and sediments. The ⁸⁷Sr/⁸⁶Sr values in carbonate nodules (0.71846 to 0.71965) of the Firozpur core are significantly more radiogenic during Last Glacial Maxima (LGM) and pre-LGM time and suggest that the Ganga river is characterized by higher ⁸⁷Sr/⁸⁶Sr values compared to global average river water (0.7119) at all times in the past and present. Sr and Nd isotopic data in silicate vary significantly with depth, 0.73580 to 0.77894 and -14.3 to -17.6, respectively and falling within the range of silicate rocks of the Higher Himalaya (HH) and the Lesser Himalaya (LH), the two major sediment sources to the Ganga river. The strong anti-correlation between ⁸⁷Sr/⁸⁶Sr and εNd again confirm this hypothesis. Together with the δ¹⁸O values and ⁸⁷Sr/⁸⁶Sr and εNd values of the Firozpur core suggest low precipitation over the HH during LGM caused less sediments supply from it and enhanced sediments supply from the LH. It shows significant influence of climate on erosion in the Himalaya.