Kinematics of Submarine Channels in Response to Bank Failures

Abstract

Submarine channel systems play a crucial role in the delivery of clastic sediments, organic carbon and pollutants across continental margins, and help define the stratigraphic architecture of deep-sea fans and their associated reservoirs. These systems generate complex lateral migration dynamics and resulting sedimentary architectures, which are often overprinted by a variety of local factors. For example, the debris from channel-wall collapses may block or restrict channel flow, thereby influencing the kinematics of stacking elements and the sinuosity of channels. Here, we investigate the responses of submarine channels to bank failures, using quantitative approaches from the Niger Delta Fulani Channel. Using 3D seismic data, we introduce a novel approach to interpreting the structural framework of channels, referred to as the structural gradient, which quantifies the relationship between sedimentary architecture and underlying structures. Bank failure mass transport deposits (MTDs) were characterised by downstream changes of cross-sectional area and the proportion of collapsed material deposited. These parameters were used to correlate the responses of channel width, thickness, aspect ratio and lateral migration, as well as the channel planform parameters (i.e., sinuosity and meander amplitude) to the occurrence of flanking MTDs. Our results demonstrate that bank failures significantly influence channel sinuosity by causing localised swings in channel pathways, impacting the overall channel morphology and stratigraphic evolution. The relationships between all channel parameters depend on the ratios of bank failures, and locations of channel-wall failures. The combined effects of bank failure confinement and structural growth control channel element stacking patterns, resulting in vertical stacks related to compensational relationships between adjacent channel complexes. Significant confinements by MTD emplacement led to rapid channel infill linked to progressive flow relaxation promoting progressive lateral mobility. Channel migration is limited by MTD accumulation to a maximum width of 1700 m. Channel lateral shift reacts to channel-wall collapses, resulting in limited lateral mobility at regional scale. We show for the first time how the kinematics of submarine channels evolved in terms of the constraints of channel-wall collapses and active structural deformation.