Climatic and Tectonic Control on the Bengal Fan Sedimentation since the Pliocene

Abstract

Strontium and Neodymium isotopic analysis of the lithogenic fractions of the hole U1445A (International Ocean Discovery Program-353) collected from the deep-water end of the Mahanadi basin (western Bay of Bengal) was carried out to evaluate the sediment sources as well as to understand the link between the temporal variations in the Sr-Nd isotope ratios and climatic and tectonic forcings during the last 6 Ma. The Sr-Nd isotopic compositions along with Fe/Al ratios and clay mineralogy show tell-tale signature of Ganga-Brahmaputra sedimentation (Bengal fan) in the study area. The significant temporal fluctuations observed in the Sr-Nd isotopic compositions suggest variation in the relative sediment contribution by the Ganga and Brahmaputra river systems, which in turn are controlled by monsoon intensity variations coupled with orographic effect, glaciation, and multiple tectonic activities. The results show the marked influence of glacial-interglacials on the relative sediment contribution by Ganga and Brahmaputra rivers during 0?1.8 Ma, while the sedimentation during the 1.8?6 Ma time window was likely influenced by both climatic and tectonic forcings such as uplift of the Shillong plateau, eastern syntaxis development of Indo-Burma wedge, reorganization of Brahmaputra river system. The present study is the first high resolution (122 samples within 6 Ma) Sr-Nd isotope ratio analysis from the Bengal Fan. The study has brought to light multiple isotope fluctuations linked to climatic and tectonic forcings. The work also establishes dominant control of Ganga-Brahmaputra sedimentation along the deep waters of the Indian east coast.