STRATIGRAPHIC ARCHITECTURE AND DISTRIBUTION PATTERNS OF SUBMARINE FAN-RESERVOIR ELEMENTS: INSIGHTS DERIVED FROM THE PLIOCENE AND PLEISTOCENE BENGAL FAN

3-D seismic data from the Bengal Fan along with spectral decomposition and RGB color blending techniques display stratigraphic architectures and spatiotemporal distribution patterns of submarine fan-reservoir elements in stark detail. Seven reservoir elements are recognized in Pliocene and Pleistocene channel-lobe complexes (i.e., subfans) developed on the northeastern fringe of the Bengal Fan. Among them, crevasse, overbank, and avulsion splays are not well acknowledged by standard models of submarine fan-reservoir elements. Crevasse splays decrease in thicknesses towards ancestral channels, and are capped by overlying levees, whereas overbank and avulsion splays increase in thicknesses towards ancestral channels and cap underlying levees. Crevasse and avulsion splays exhibit lobate planform morphology and are linked updip to ancestral channels by feeder channels, whereas overbank splays display tongue-like planform morphology and lack feeder channels. Fills of laterally migrated channel-complex sets (CCSs) appear only in early stage of subfan evolution, whereas fills of vertically stacked CCSs can appear either in middle or late stages of subfan evolution. The inner segment of the documented subfans fostered infills of both laterally migrated and vertically stacked CCSs, whereas the outer segment of the studied subfans contains terminal lobe complexes and distributary-channel fills. Crevasse, overbank, and avulsion splays can appear either in middle or late stages of subfan evolution, and mainly occur in overbank environments of middle segments of the documented subfans, which are dominated by muddy facies as predicted by the standard model of submarine fan-reservoir elements. Pliocene and Pleistocene subfans demonstrate the importance of splay processes in submarine-fan evolution, and this has implications for understanding the evolution of the volumetrically largest sediment accumulations on Earth and the distribution of submarine fan-reservoir components. The downlap of subsequent levees onto crevasse splays and overbank splays created stratigraphic traps with the potential for large hydrocarbon accumulations.