Abstract:

Submarine channels are a frontier topic in deepwater sedimentology. Multi-stage channels usually migrate and evolve nonuniformly. Submarine channels in the Rakhine Basin, however, exhibit a gradual change in their geomorphology and architecture since the Late Miocene. The genesis of such gradual change is poorly understood. In this study we conducted 3D seismic investigation into the geomorphology, sedimentary characteristics, genesis and evolution of the Rakhine submarine channels. Architecturally, the Rakhine submarine channels show a gradual increasing of levee development and decreasing of undercutting. Specifically, Late-Miocene channels lack overbank levees, and erosion is predominant. Pliocene channels are characterized by mixed leveed and non-leveed channels and concurrence of deposition and erosion. Whilst Quaternary channels are flanked by extensive levees, and channel deposition is predominant. Morphologically, the Rakhine submarine channels display a gradual decreasing of erosion scales but a gradual increasing of sinuosity. Specifically, Late-Miocene channels exhibit large-scale undercutting, and are wide and deep, with a large cross-section but low sinuosity. Pliocene channels are characterized by moderate erosion, channel size and sinuosity. In comparison, Quaternary channels show reduced undercutting and channel size, but higher sinuosity. Such gradual change in channel morphology and architecture can be attributed to the gradual, westward migration of the Brahmaputra River sediment-routing system since the Late Miocene which led to gradual decreasing of extra-basinal sediment supply and subsequent development of gravity flows to bring the observed changes in submarine channels.

Key words: Bay of Bengal, submarine channels, morphologic characteristics, architecture, gradual transition, source-to-sink genesis