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Submarine channel systems play a crucial role in governing the delivery of sediments and pollutants such as plastics from the shelf edge to deep water. Understanding their distribution in space and time is important for constraining the locus, magnitude, and characteristics of deep-water sedimentation and for predicting stratigraphic architectures and depositional facies. Using three-dimensional seismic reflection data covering the outer fold-and-thrust belt of the Niger Delta, we determined the pathways of Miocene to Pliocene channels that crossed, at 173 locations, 11 fold-thrust structures for which the temporal and spatial evolution of strain rates has been constrained over a period of 11 m.y. We use a statistical approach to quantify strain and shortening rate distributions recorded where channels have crossed structures compared to the fault array as a whole. Our results prove unambiguously that these distributions are different. The median strain rate where channels cross faults is <0.6%/m.y. (~40 m/m.y.), 2.5× lower than the median strain rate of active fault segments (1.5%/m.y.) with a marked reduction in the number of channel-fault crossings where fault strain rates are >1%/m.y. Our results quantify the sensitivity of submarine channels to active deformation at a population level for the first time and enable us to predict the temporal and spatial routing of submarine channels affected by structurally driven topography.

Over the past two decades, the increased availability of three-dimensional (3-D) seismic data and their integration with outcrop and numerical modeling studies have enabled the architectural evolution of submarine channels to be studied in detail. While tectonic activity is a recognized control on submarine channel morphology, the temporal and spatial complexity associated with these systems means submarine channel behavior over extended time periods, and the ways in which processes scale and translate into time-integrated sedimentary architecture, remain poorly understood. For example, tectonically driven changes in slope morphology may locally enhance or diminish a channel’s ability to incise, aggrade, and migrate laterally, changing channel kinematics and the distribution of composite architectures. Here, we combined seismic techniques with the concept of stratigraphic mobility to quantify how gravity-driven deformation influenced the stratigraphic architecture of two submarine channels, from the fundamental architectural unit, a channel element, to channel complex scale, on the Niger Delta slope. From a 3-D, time-migrated, seismic-reflection volume, we evaluated the evolution of widths, depths, sinuosities, curvatures, and stratigraphic mobilities at fixed intervals downslope as the channel complexes interacted with a range of gravity-driven structures. At channel element scale, sinuosity and bend amplitude were consistently elevated over structured reaches of the slope, displaying a nonlinear increase in length, perpendicular to flow direction. At channel complex scale, the same locations, updip of structure, correlated to an increase in channel complex width and aspect ratio. Normalized complex dimensions and complex-averaged stratigraphic mobilities showed lateral migration to be the dominant form of stratigraphic preservation in these locations. Our results explain the intricate relationship between the planform characteristics of channel elements and the cross-sectional dimensions of the channel complex. We show how channel element processes and kinematics translate to form higher-order stratigraphic bodies, and we demonstrate how tectonically driven changes in slope develop channel complexes with distinct cross-sectional and planform architectures.

The processes and deposits of deep‐water submarine channels are known to be influenced by a wide variety of controlling factors, both allocyclic and autocyclic. However, unlike their fluvial counterparts whose dynamics are well‐studied, the factors that control the long‐term behaviour of submarine channels, particularly on slopes undergoing active deformation, remain poorly understood. We combine seismic techniques with concepts from landscape dynamics to investigate quantitatively how the growth of gravitational‐collapse structures at or near the seabed in the Niger Delta have influenced the morphology of submarine channels along their length from the shelf edge to their deep‐water counterpart. From a three dimensional (3D), time‐migrated seismic‐reflection volume, which extends over 120 km from the shelf edge to the base of slope, we mapped the present‐day geomorphic expression of two submarine channels and active structures at the seabed, and created a Digital Elevation Model (DEM). A second geomorphic surface and DEM raster—interpreted to closer approximate the most recent active channel geometries—were created through removing the thickness of hemipelagic drape across the study area. The DEM rasters were used to extract the longitudinal profiles of channel systems with seabed expression, and we evaluate the evolution of channel widths, depths and slopes at fixed intervals downslope as the channels interact with growing structures. Results show that the channel long profiles have a relatively linear form with localized steepening associated with seabed structures. We demonstrate that channel morphologies and their constituent architectural elements are sensitive to active seafloor deformation, and we use the geomorphic data to infer a likely distribution of bed shear stresses and flow velocities from the shelf edge to deep water. Our results give new insights into the erosional dynamics of submarine channels, allow us to quantify the extent to which submarine channels can keep pace with growing structures, and help us to constrain the delivery and distribution of sediment to deep‐water settings.

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