Sediment provenance in the Bay of Bengal using Sr and Nd isotopes

Abstract

The Bay of Bengal receives large volume of sediments discharged through seven major rivers, the largest of them being the Ganga and the Brahmaputra River systems (G-B). These sediments preserve records of the sediment discharged from these rivers. Sediment composition of the Bay of Bengal appears to be mainly governed by three processes, viz., detrital, biogenic and diagenetic, with detrital being the dominant in this region. Their input reveals physical and chemical erosion of the terrain over which they flow and is strongly dependent on the monsoon intensity, especially the southwest or summer monsoon. The sediment deposition in the Bay of Bengal is significantly influenced by the seven rivers draining into it with major contributor being the Ganga and Brahmaputra river system. The climate is one of the major driving force incontrolling sediment deposition in the Bay of Bengal with monsoon playing a pertinent role in it. To understand these processes, chemical and isotopic measurements were carried out in several surface sediments of various cores and depth profiles of two sediment cores from the Bay of Bengal. The sediments derived from the various river sources and distributed in the Bay of Bengal should mimic the signatures of their provenance. Sr and Nd isotopic composition measured on the silicate fraction of the surface sediments show strong influence of G-B rivers in the northern Bay of Bengal with high ⁸⁷Sr/⁸⁶Sr (0.725-0.735) and low ∈Nd (-18 to - 12). The samples from the western Bay of Bengal show mixed signature of Sr and Nd isotopes derived mainly from the rivers draining in the western continental margin of India. The samples from the Andaman Sea have least radiogenic Sr and more radiogenic ∈Nd, supposed to be influenced by sediments from the Irrawaddy River. The sediment core studies from the Bay of Bengal suggest the supply of low radiogenic ⁸⁷Sr/⁸⁶Sr from the Irrawaddy River to be a likely contributor for high radiogenic ∈Nd due to an enhanced NE Monsoon during LGM.