Morphological and architectural evolution of submarine channels: An example from the world's largest submarine fan in the Bay of Bengal

Abstract

The characteristics and evolution of different types of channel-complex sets (CCSs) have long attracted attention from both academia and the oil industry. 3D seismic data from the world's largest submarine fan in the Bay of Bengal allow the exploration of morphology, architecture, and evolution of a Pleistocene submarine channel system from inception to abandonment. Four types of architectural elements are recognized, including feeder and distributary channel-complex set (CCS), levees, bend cutoffs, and incised and unincised crevasse splays. Three types of CCSs are recognized: (1) erosional non-leveed CCSs with the lowest values of channel width (W), thickness (T), and cross-sectional area (Ca) (mean values of W = 153 m, T = 20 m, and Ca = 2613 m2); (2) graded CCSs with the highest values of W, T and Ca (mean values of W = 745 m, T = 89 m, and Ca = 49183 m2); (3) aggradational leveed CCSs with intermediate values of W, T and Ca (mean values of W = 476 m, T = 56 m, and Ca = 21968 m2). Graded CCSs and aggradational leveed CCSs have overbank levees, crevasse splays and bend cutoffs, whereas erosional non-leveed CCSs lack these features. Such architectural difference in overbank deposits suggests a channel evolution pattern of initial incision (erosional non-leveed CCSs) and then aggradation (graded and aggradational leveed CCSs), resulting in a pattern of incision-to-aggradation channel evolution. An increase-then-decrease in channel morphometrics (represented by W, T, and Ca) from erosional non-leveed CCSs with the lowest mean values of W, T, and Ca, to graded CCSs with the highest mean values of W, T, and Ca, and finally to aggradational leveed CCSs with the intermediate mean values of W, T, and Ca suggest that the incision-to-aggradation channel evolution is related to waxing-then-waning energy cyclicity. Submarine channel turbidity flows during the waxing energy phase became progressively more energetic and increasingly more erosional, producing erosional non-leveed CCSs. Instead, submarine channel turbidity flows during the waning energy phase were more diluted and increasingly more depositional, thereby producing aggradational leveed CCSs. The phase of peak environmental energy was most likely accompanied by most energetic turbidity currents, resulting in graded CCSs. Results and observations from the current study contribute to a better understanding of architectural complexity and evolution of submarine channels.