Morphology and Architecture of Recent Valley-Channel Complex of the Bengal Fan

Venkatarathnam Kolla¹, Anindya Bandyopadhyay², Pasnkaj Gupta², Brunti Mukherjee², and D. V.Ramana^2
1Consulting services, Houston, TX
²Petroleum Division, Reliance Industries, Navi Mumbai, India

Multi-beam and 3D seismic data of the northern, proximal part of the most recent valley-channel complex of the Bengal Fan show that it actually consists of several valleys, each successively shifted to the left or to the right of, or completely contained within the preceding valleys. Each of these valleys has their own levee-overbanks.

The entire valley-channel complex is broadly sinuous. Each valley fill consists of several highly sinuous under-fit channel fills. The sinuosity of the last-phase under-fit channel in the uppermost valley fill, now exposed on the sea-floor, may be as much as 2.5 to 3.0. Each of the under-fit sinuous channel fills is laterally highly migratory for much of their history ending in more vertically aggrading phases. Down-stream sweeps and cut-offs are very common in the evolution of these sinuous channels. 3 D seismic-amplitude slices of these sinuous channel-floor fills, their banks and to some extent their overbanks--all show much apparent resemblance to aerial photos of the networks of scrolls of point-bars and cut-offs of fluvial meandering systems. However only the scrolls of deep-water channel-floor fills, with high seismic amplitudes, are inferred to be much sand-prone. The entire valley complex consists of several storeys (layers) of the under-fit sinuous channel fills with a total thickness of several hundred meters. The overbanks of successive valleys when they abut against the banks of especially the larger preceding valleys result in the formation of terraces. With the overbanks included, the widths of the entire valley-overbank complex are several tens of kilometers wide.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas