Depositional dynamics of the Bengal Fan since the Late Miocene: discrimination of skinfriction shear stresses of hemipelagic vs. turbiditic deposition.

The Bengal Fan covers the entire floor of the Bay of Bengal (BoB) and has accumulated erosional material from the Himalayas since the Early Eocene. The fan architecture is constructed by turbidity current deposits via channel levee systems during active fan progradation and hemipelagic sedimentation during periods of local fan inactivity. In the present study, we document the fan development, sedimentation history, and depositional processes in the lower Bengal Fan and present a site-to-site comparison of stratigraphy and channel migration since the Late Tortonian (ca. 7.5 Ma) from sedimentological and physical property records at Site U1451 of IODP Expedition 354 to 8°N in the lower Bengal Fan. Fine sediment (Sortable Silt, SS) textural and sorting records are used to reconstruct the current skinfriction shear stress in the Benthic Boundary Layer (BBL) of the BoB. Also, a distinction in shear stress environment between turbidity dominated active fan and background hemipelagic fan growth is presented. A criterion is set in the following paper to validate the use of SS records in hemipelagic deposits in the BoB to decipher the shear stress regimes of depositing flows on the basis of sand weight percentage and mean SS sizes (S͞S) variation. This study will enhance our understanding of the Bengal Fan deposition dynamics and fan development with the reconstructed shear stress regimes associated with various depositing flows (turbidity current and/or deep water circulation). It will provide a strong base to model fan internal processes and material flux to the BoB. [ABSTRACT FROM AUTHOR]