Reconstructing the late Miocene to recent volcanic, geologic, and oceanographic evolution in the Andaman Sea and Northern Bay of Bengal, Northeast Indian Ocean

This dissertation aims to reconstruct the volcanic, geologic, and oceanographic evolution in the Andaman Sea and northern Bay of Bengal regions during the last ~9.4 Myrs. The volcanic evolution of the north Sunda Subduction Zone is investigated through geochemical (i.e., major, trace, and rare earth elements) and isotopic (Pb-Hf-Nd) analysis of volcanic ashes (Chapter 2). The geochemistry of volcanic ashes from the Andaman Sea suggests that they were derived from a northern Sumatra source region with a magma chamber that underwent fractional crystallization in addition to sediment and/or continental crust assimilation. The identification of unconformities (Chapter 3) in records from the Andaman Sea (~3.8-2.6 Ma) and northern Bay of Bengal (~3.8-3.65 Ma; ~2.55-1.96 Ma) are documented using a detailed nannofossil age model and further characterized through CaCO3, biogenic silica, lithogenic, and organic carbon MARs. The age and duration of the unconformity in the Andaman Sea coincides with basin-wide paleobathymetric shoaling and was most likely caused by localized tectonic uplift that resulted from either active backarc spreading, growth of the accretionary wedge, or a combination of both. The unconformities in the northern Bay of Bengal were likely the result of sediment erosion induced by enhanced involvement of coincident with intensification of the Asian Monsoons (~5 Ma). This record also includes an older interval (-5.54-3.65 Ma) devoid of calcareous nannofossils that represents a period of extensive CaCO3 dissolution. This dissolution may have been localized and driven by enhanced organic carbon delivery and decomposition at Site 19. Finally, the evolution of deep water influence in the Andaman Sea and northern Bay of Bengal regions was further studied through the use of biogenic silica MARs as a proxy for paleoproductivity (Chapter 4). An abrupt decrease in biogenic silica MARs at these sites suggests a decrease in nutrients occurred at ~6 Ma, coincident in time with estimates for the closure of the Indian-Pacific teleconnection via the Indonesian Throughflow. This closure would have restricted the flow of nutrient-rich Pacific Ocean waters to the Andaman Sea and northern Bay of Bengal regions and may explain the abrupt decrease in productivity preserved in these records.