Fingerprints of Tectonics and Climate Change in the Detrital-Zircon U–Pb Record of the Deep-Sea Bengal Fan

The Himalayan-sourced Ganges–Brahmaputra (GB) river system and the deep-sea Bengal Fan represent Earth’s largest source-to-sink sediment-dispersal system. IODP Expedition 354 (2015) drilled a 7-site transect in the middle Bengal Fan, ~1400 km south of the shelf margin. This presentation features a detrital-zircon (DZ) U–Pb provenance record from IODP 354 cores and modern river samples, which provides insight into tectonic and climatic controls on sediment routing.

Bengal Fan turbidites record the strong tectonic and climatic forcing associated with the GB system. First, India’s NNE motion relative to Asia places IODP 354 drill sites ~800 km and ~400 km farther south from the GB delta at 20 Ma and 10 Ma: prior to 10 Ma, these locations remained too far away for significant sand-rich turbidite deposition, whereas after 10 Ma thick sand-rich turbidites are common. Second, after ~4000 km of fluvial and turbiditic sediment transport, the DZ U–Pb record faithfully records Himalayan and Tibetan sources, especially the <300 Ma ages from the Gangdese arc in Tibet, which is present by the Early Miocene, and increases in significance over time. Third, we infer signals of climate change in the Plio–Pleistocene record. For example, sand-rich turbidites accumulated only during glacial periods of low sea level when river mouths connected directly with slope canyons. Moreover, sand-rich turbidites display different proportions of U–Pb age groups than modern river sands, especially after the Plio–Pleistocene transition. We speculate these differences reflect interglacial vs. glacial sediment production: glacial climates are more closely tied to higher-elevation cold-climate and glacial processes.