Submarine Sediment Distribution Patterns within the Bengal Fan System, Deep Water Bengal Basin, India
Thomas, Bruno; Despland, Patrick; Holmes, Lance
Santos Ltd, Adelaide, SA, Australia.
The Bay of Bengal is home to the world's largest submarine fan. This system has developed since the Eocene predominantly in response to the Himalayan orogeny. A third of the sediments discharged annually by the Ganges-Brahmaputra river system are reportedly making their way into the deepwater at present day. Sediment supply to the fan is primarily controlled by the Swatch of No Ground, a prominent 15km wide Pleistocene canyon connecting the shallow shelf and Ganges-Brahmaputra delta to the deepwater.
Santos proprietary seismic dataset in the northern Bay of Bengal covers over 16000sq.km of the continental slope-upper fan transition. A circa 3500sq.km 3D survey acquired in addition to the 2D grid facilitates seismic attribute analysis and further refinement of the depositional model.
Study of the modern-day morphology of the Bengal Fan provides unique insights into resolving past depositional patterns and ultimately increases our understanding of the petroleum prospectivity. The area of interest is characterised by a well defined shelf edge, locally affected by slumping and mass wasting events, but with a notable absence of significant growth faulting frequently present in other large delta systems. The present canyon feeder system cuts erosively through the shelf edge, passing down-slope into depositional channel systems in the proximal part of the fan. The upper fan in dominated by large-scale, sinuous and aggradational Channel Levee Complexes (CLCs). A channel avulsion depositional model appears to fit geometries observed seismically, with basal High Amplitude Reflective Packages (HARPs) units being ultimately overrun by the CLCs. The process is repeated temporally throughout the section at various scales, this being dependent upon sedimentation influx rate and frequency of avulsion. The overall trend shows CLCs decreasing in size with depth, which is in accordance with a progradational model for the Bengal delta/fan system.
Detailed depositional analysis is key to defining sand-prone fairways, potential sealing units and trapping configurations in the system. In the absence of well data, analogy with proven deepwater submarine fans system worldwide is considered essential in evaluating this underexplored basin.
To the reviewers: please note Dr Thomas is on leave until the 30th of January. He might submit an updated abstract early February. My apologies for any issues this may cause, regards Patrick Despland
AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012