Different avulsion events throughout the evolution of submarine channel-levee systems: A 3D seismic case study from the northeastern Bengal Fan

Abstract

As very common deep-water phenomena, submarine channel avulsions have been paid considerable attention recently. The differences among them are, however, rarely noted, nor their relationship to the evolution of submarine channels. A seismically well-imaged channel-levee system from the Pliocene Bengal Fan, named target channels (TCs) and consisting of three independent channels (Tc1-Tc3), has been selected as a case to address these issues. Using high-resolution 3D seismic data along with spectral decomposition and RGB color blending techniques, this study images TCs from initiation to abandonment and recognizes three different types of avulsion events: regional avulsion, local avulsion and bank crevasse. In the early evolution stage of TCs, the regional avulsion and the local avulsion successively occurred, promoting TCs to obtain a stable flow course and then undergo a significant evolution. Moreover, coupled with those regional and local avulsion events, TCs were growing respectively in the form of individual channel and amalgamated stacking. In the late evolution stage of TCs, only bank crevasses occurred and led to the formation of crevasse splays in the overbank setting, which coincided with the aggradational stacking of TCs developing. This new evolution model of channel-levee systems, which acknowledges different avulsion events, may provide insights on the understanding of analogue deep-water deposits and in turn can be applied to guide the hydrocarbon exploration and development.