Flow processes of the interaction between turbidity flows and bottom currents in sinuous unidirectionally migrating channels: An example from the Oligocene channels in the Rovuma Basin, offshore Mozambique

Abstract A number of unidirectionally migrating channels have been interpreted as the result of the interaction between turbidity flows and bottom currents. Based on the analysis of the morphology and internal architecture of channels, different conceptual models of unidirectionally migrating channels were built to reveal the flow process of the interaction between turbidity flows and bottom currents. Most previous studies mainly focused on the straight section of channels, however, the relevant models did not elucidate the flow process in sinuous sections, limiting the knowledge on the formation mechanism and evolution of the whole unidirectionally migrating channels. By using 3D seismic data, the current study not only depicted the geomorphology and internal architecture of a sinuous unidirectionally migrating channels in the Rovuma Basin, offshore Mozambique, but also quantitatively analyzed the flow processes in the straight and bend sections of the channels. The results show that the interaction between turbidity flows and the northward-flowing Antarctic Bottom Water (AABW) led to the unidirectional migration of the turbidite channels. In the straight section of channels, fine-grained material from the upper parts of turbidity flows was deflected northward via flow stripping induced by the AABW, and this material was finally deposited as sandy lateral accretion packages and muddy drifts. The lateral deposits steepened northern channel banks and forced the southward migration of channel axes. However, in the bend section of channels, the upper parts of turbidity flows were forced towards the inner (southern) bank due to the helical flow induced by centrifugal forces, which probably offset the effect of the AABW, and therefore no lateral drifts developed. The effect of bottom currents on turbidity flows is related to the relative direction of turbidity flow and bottom currents. The lateral deposition and corresponding erosion induced by bottom currents influence the formation of the unidirectionally migrating channels, and the channels migrate towards the erosional side but away from the lateral deposition. Our results can help reveal the complete flow processes and sedimentation in the unidirectionally migrating channels in deep water basins around the world.