The youngest channel-levee system of the Bengal Fan: results from digital sediment echosounder data

A high-resolution seismic survey focused on the youngest channel-levee system of the Bengal Fan was carried out during January/February 1994 from the RV Sonne. Acoustic strata patterns and the downslope development of the channel-levee system were examined with the parametric sediment echosounder PARASOUND. Determination of the age of the sedimentary strata shows turbiditic activity during sea level rise and highstand. The initial formation of the system in the middle fan occurred in the late glacial and outer levee growth stopped with glacial termination. Several vertical, aggradational segments constitute the inner levees created in the Holocene, The formation of the inner levee segments indicates the constriction of a formerly 14 km wide channel in discrete phases. The top of the segments form topographic pinnacles, explaining the morphology of other channel-levee systems from other fans in the world's oceans. Some cross-sections from the lower fan reveal lenticular channel-levee systems with common reflection characteristics. Prograding distinct reflections on the outer side of the upper levees terminate with a downlap against an unconformity, which separates the upper part of the overbank deposits from a mostly diffusely reflecting lower part. Channel constriction has also been observed in the lower fan. Two models are introduced to explain the generation of the most common acoustic strata patterns by sea level fluctuations or downslope shifting of the channel mouth. (C) 1997 Elsevier Science B.V.