Spatial distribution of bedforms and related flow processes around canyon mouths: Insights from the Rovuma Basin (offshore Mozambique)

Bedforms associated with turbidite systems are commonly observed on seafloor. Previous studies have analysed bedform morphological and sedimentary features to determine their formation mechanisms and flow dynamics. However, the seafloor topography and ocean circulation have comprehensively influenced both down- and along-slope turbidity flow processes, complicating the spatial distribution of the related bedforms. Three-dimensional seismic data (3D) were used to depict the morphological and sedimentary features of the bedforms around the canyon mouth on the slope of the Rovuma Basin (offshore Mozambique), to reveal the spatial distribution and related flow processes of the bedforms. The results show that the spatial morphological and sedimentary features of the submarine bedforms at canyon mouths are controlled by the combined action of down- and along-slope factors. The along-slope bottom currents influence the deposition distribution of the turbidity current at the canyon mouth. However, slope breaks control bedform morphological and sedimentary features during downslope turbidity currents. Coarse-grained material of turbidity current flows along the axial zone of the canyon mouth, forming a linear series of crescent-shaped net-erosional cyclic steps characterized by short steep stoss sides and long gentle lee sides. The fine-grained material of the turbidity currents is deflected towards the northern flank of the axial zone by the bottom currents and deposited as undulating net-depositional cyclic steps at upper reach of the northern flank, showing long gentle stoss sides and short steep sides. Slope breaks enhance the erosion on cyclic steps by altering the velocity of turbidity current, forming net-erosional cyclic steps with the manifestation of both short and steep stoss and lee sides at lower reaches of northern flank. The turbidity current in the axial zone formed lateral flow diversions caused by the obstruction of the cyclic steps. The flow diversions converge with the downslope flowing unconfined turbidity current at the northern flank and constitute a confluence characterized by continuous variation of flow properties, forming the cyclic steps featuring irregular morphology.