Frequency of deep-sea turbidity as an important component of the response of a source-to-sink system to climate: A case study in the eastern middle Bengal Fan since 32 ka

Abstract

The Bengal Fan is world famous for its developed turbiditic system. This study identified turbidite records in a gravity core (BoB-104) taken from near a currently inactive channel (E4) based on lithology, geochemical and mineralogical parameters. This core contained turbidite and hemipelagic layers in this core. This study identified 21 turbidite layers which exhibited consistent provenance with the hemipelagic layers, showing a two end-member mixing pattern and indicating consistent sources since the last glacial period. Typical turbidite layer analysis was used to study the possible turbidite deposition mechanism. Features such as the lithology break interface, normal graded sequence, a consistent pattern of a sharp increase and gradual decrease in the variation of the mean grain size (Mz), and median grain size (D50) and Si/Al ratios commonly implied a continuous deposition in accordance with variations in densities and particle sizes. This study identified long-term evolution of turbidite deposition in the eastern middle Bengal Fan that appears to be the last and indispensable part of the systematic response of the “Bengal depositional system” to the climate. Four stages were identified from the turbidite records and all the identified intervals showed synchronous changes with the entire system. The Indian summer monsoon (ISM) played a dominant role in the system interactions. The sea level affects the turbidity system by regulating the transition of the deposition center between the deep-sea and the shelf, whereas the migration of the main channel to the “Active Valley (AV)” between 14.5 ka to 10.4 ka almost halted the deposition of turbidites along the E4 channel. Thus, turbidity activity in the eastern middle Bengal Fan is not an isolated incident but part of a comprehensive system resuling from global and regional changes at different scales.