The Architecture and Evolution of Deepwater Sedimentary Elements in One Study Area within Upper Bengal Fan

Key words: 
• Bengal fan /
• deepwater sedimentary elements /
• seismic facies /
• vertical pattern /

Abstract: Like Amaon fan and Mississippi fan, Bengal fan is a favorable field for investigating  sedimentary process in deepwater. Considering lacking coring and well data, highresolution 3D seismic data from the study area was analyzed to study the architecture and evolution of sedimentary elements on the upper Bengal Fan. the area of interest belonged to deepwater region, and stratigraphy was formed in marine deposition. Six typical seismic facies have been identified, which were incised channel fill facies, gull wingshaped facies, wedgeshaped divergent facies, transparent facies, highamplitude parallel facies and lowamplitude parallel facies. Seismic Facies 1 was interpreted as coarsegrained deposits of abandoned channels. Seismic Facies 2 represented channellevee complex. Seismic Facies 3 was interpreted as finegrained levee sediments. Seismic Facies 4 represented mass transport deposits. Seismic Facies 5 was interpreted as lobes，which was different from sheet sand interpreted by predecessors. Seismic Facies 6 represented hemipelagic drapes and fills. On seismic profile lobex and channels display high amplitude, which means coarse lithology deposition, and may be good reservoirs. Through analysis of SN and EW seismic profiles reflection charateristics, seismic attribute planeform, we revealed the sedimentary evolution: during the period of SQ1, lobes were deposited, and turbidute flow tansported sediments far into basin; main deepwater elements of SQ2 were channels and levees, with channel migrating from SE to NW; Sedimentary elements of SQ3 were lobes, locally MTDs originated from slides, slumps and debris flow; channelleveed complex mainly dominated the stratigraphy of SQ4.