Linking Miocene-Pliocene Provenance Signals of the Ancestral Brahmaputra River of the Indo-Burman Ranges with Associated Deepwater Deposits of the Bengal and Nicobar Fans
Abstract
A rich record of Cenozoic Himalayan denudation is preserved in the outcrops of the Indo-Burman Ranges (IBR) fold and thrust belt and within the deepwater sediments of the Bengal and Nicobar Fans (BNF), but these coupled depocenters have yet to be linked in terms of provenance and age. We re-evaluate the lithostratigraphy of the IBR through a time-transgressive lens, using Holocene depositional environments of the Ganges-Brahmaputra delta (GBD) as modern analogs to their Miocene counterparts in the IBR. We then compare detrital zircon U-Pb data from the IBR with published data from recent IODP 354 drilling transects within the Bengal Fan to uncover provenance relationships across the source to sink system. Four shallow marine/intertidal and three fluvial facies exhibit characteristics of the modern GBD and allow paleogeographic reconstructions of the ancient delta. The F2 facies of the IBR represents the channel-belt sands of a large river system that delivered sediments to the now folded proto-deltaic basin and BNF, whereas the M1-M3 facies record progradation of the ancient subaqueous delta across the paleoshelf. Multi-dimensional scaling (MDS) analysis from the IBR facies reveals a shift from a mixed Ganges-like and Himalayan provenance in shallow marine and intertidal IBR deposits to an increasingly Brahmaputra-like signal in fluvial deposits, indicating shelf mixing of non-confluent Ganges and Brahmaputra Rivers during Miocene progradation. BNF deposits exhibit oscillations between Himalayan and Tibetan signals reflecting periods of mixing and avulsions of the two paleo-rivers. The Miocene Brahmaputra primarily fed the Nicobar Fan east of the 90E Ridge until the rising Shillong massif forced its avulsion to the west. This 400 km westward shift facilitated the merging of the Ganges and Brahmaputra River deltas and a larger input of Brahmaputra sediments into the Bengal Fan. Our results begin to fill a temporal and spatial knowledge gap in the long-term evolution of the world's largest depositional system.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T23C0387S
- Keywords:
-
- 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8169 Sedimentary basin processes;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICSDE: 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS