Sediment Pathways and Emergence of Himalayan Source Material in the Bay of Bengal

Abstract

The sediment succession in the Bay of Bengal (BoB) records the signatures corresponding to India-Asia collision, regional climate change, and erosional processes of both the Himalayan orogen and Indian subcontinent. The Bengal Fan-the world's largest submarine fan-has long been studied to understand the link between the Himalayan tectonics and Asian monsoon. But, lack of detailed information on corresponding signals hampered the understanding of related processes of tectonics, climate and erosion. The present study of long-streamer seismic reflection profile data and information from deep drill well logs in the western BoB has revealed two different phases of sediment deposition. In the first phase, until Oligocene-Miocene (~23 Ma), Indian peninsular rivers discharged sediments to the BoB which accumulated at a rate ~20 m/m.y. with an aberration of two fairly enhanced sediment pulses during the periods from 65 to 54 Ma and 34 to 23 Ma. In the second phase, since 23 Ma, the Ganges and Brahmaputra rivers added huge volumes of sediments to the bay at variable rates ranging from 40 to >1000 m/m.y. A distinct increase in sediment discharge (~140 m/m.y.) during the Oligocene-Miocene (~23 Ma) together with the development of regional onlap unconformity and the start of turbidity system provide an important age marker corresponding to rapid exhumation of the Himalaya, which intensified the erosional process and commencement of Bengal Fan sedimentation. Further rise in the rate of sedimentation during the period 6.8-0.8 Ma is coincident with the change in monsoon intensity, but surprisingly not in agreement with the decrease in sediment rate reported at ODP Leg 116 sites in the distal Bengal Fan. Here we provide wellconstrained ages for the commencement and growth of the Bengal Fan, which can serve as benchmark information for understanding the interaction between the Himalayan exhumation and Asian climate.

Magnetic Mineralogical Approach for the Exploration of Gas Hydrates in the Bay of Bengal

“…Changes in monsoons, Himalayan uplift, weathering intensities, erosional processes in peninsular India, and glacial/interglacial cycles influenced the supply of detrital particles to the K‐G basin (Curray et al, ; Colin et al, ; Krishna et al, ; Rao & Kessarkar, ; Sangode et al, ; Weber et al, ). The K‐G basin receives a large sediment load from peninsular India through the Krishna and Godavari rivers.…”

“…The proximal shale bulges continued to grow during the Pliocene due to ongoing sedimentation in the shelf region while distal bulges ceased to grow during this period. Increased sediment flux at 0.8 Ma due to increased deformation in the Himalayas (Clift et al, ) led to the formation of mega depocenters in the shelf region (Krishna et al, ). We propose that this increased late Pleistocene sedimentation might have accentuated the shale bulge growth, which appears as bathymetric mounds on the seafloor.…”

“…Later, as sedimentation increased during the Pleistocene, this region was exposed to rapid uplift and faulting as a result of shale‐tectonism that was triggered by rapid sediment loading (Dewangan et al, ; Krishna et al, ). Highly pressurized strata were generated as a result of higher sedimentation rates that triggered growth of faults, folds, and upthrusting features (bathymetric mounds and ridges) in the K‐G basin.…”

“…These structures likely acted as conduits for upward fluid/gas migration to enter the gas hydrate stability zone (Dewangan et al, ; Shankar & Riedel, ). A fivefold late Pleistocene sedimentation rate increase in the K‐G basin (Krishna et al, ) led to the generation of large MTDs that were deposited rapidly and provided the pressure and temperature conditions needed for gas hydrate nucleation (Figure S2). The highest gas hydrate saturations occur within magnetically enhanced Z‐III in all studied cores (Figure ; Collett et al, ; Kumar et al, ).…”

Response of Cenozoic turbidite system to tectonic activity and sea-level change off the Zambezi Delta

“…In general, this interplay can be interpreted from geophysical and sedimentological datasets, where these are available, allowing fans to be ultimately linked to a handful of controlling parameters. The formation and growth of the largest submarine fan, the Bengal Fan, trace their origin to the Himalayan orogeny and the monsoon climate that controls sediment supply in the Indian subcontinent (Curray et al 2003;France-Lanord et al 2015;Krishna et al 2016). The morphology and growth of the Amazon Fan, in contrast, are linked to the intensification of weathering and erosion of the Andes during their Late Miocene uplift at a time of rapid sea level variations during glacial and interglacial cycles (Figueiredo et al 2009;Flood et al 1991;Gorini et al 2014;Milliman et al 1975).…”