Abstract Deformation above mobile salt along continental margins results in a complex array of structures that have a profound effect on sea-floor geomorphology and create a slope characterised by a 3D array of salt-cored highs and intervening sub-basins. We present examples of the various ways the growth of salt-related fold and fault arrays controls submarine channel complexes at local to regional scales using standard attributes, spectral decomposition and RGB blending of 3D seismic datasets from Tertiary passive margins. Sediment transport pathways commonly divert around salt-cored highs and become fixed by early-formed structures high on the slope resulting in long-lived, major sediment (channel complex) fairways that are ‘pinned.’ During early stages of fold growth channels tend to be simple and isolated and are orientated perpendicular to the regional slope. However, as folds grow and interact, the channel belts increase in sinuosity and their cross-sectional and long-profile geometry becomes progressively more variable and complex as slope roughness increases. As a result, channel orientations become increasingly variable with local deviations parallel to fold axes and channel complex sinuosity mimicking the spacing of the main salt-cored structures. Avulsion nodes, channel complex depth and width, levee development, and the internal architecture of component depositional elements within channel complexes all show systematic variation with respect to structural location. Amplification of salt-cored folds and growth of diapirs also leads to local oversteepening and slope failure resulting in development of mass transport complexes that may dam entry or exit points between mini-basin depocentres.

Abstract High-resolution seismic stratigraphic and geomorphic analysis reveals the evolution of a shelf to intraslope basin on the Santos Basin continental margin, offshore Brazil. Within a late Cretaceous framework of high confidence 3D-seismic-stratigraphic correlations, exceptional quality seismic-geomorphic beach-ridge-, canyon-, channel- and lobe-elements are analyzed with particular focus on their temporal and spatial relations. Shallow and deep marine, partly gravity-driven processes associated with depositional outbuilding of the continental margin generate local gradients and sea-floor topography that determine cyclic changes in aggradational and degradational patterns. This is manifested in the proportion, distribution, size, shape and orientation of shoreline, shelf edge, canyon, slope-channel and intraslope submarine fan depositional elements. The evolution of the continental margin is a response to the dynamic changes in sediment delivery, shelf accommodation, local slope gradient, seafloor topography, and mobile salt substrate geometry. The study documents significant sandy submarine fan deposition development along an over-all high accommodation margin, typically associated with higher frequency episodes of relatively low shelf accommodation expressed as normal progradation, flat shoreline trajectory, and narrow (<10km width) shelf development. Genetically connected, continuous sediment fairways develop and span from beach-ridge/shore-face systems via combined shelf/slope positioned canyon to intraslope basin submarine fan systems. Longshore drift and/or storm re-suspension processes is inferred to deliver sandy sediment to shelf-portion of submarine canyon. Farther down-dip transport and deposition is driven by gravity flows. The observed (wide) longitudinal to lateral aspect ratio (~10 km × ~20 km) is explained as a direct response to the salt-influenced intraslope basin topography, as well as significant lateral-directed drive to fan growth relative to basin-restricted longitudinal (downdip) growth. Negative shelf accommodation manifested by subaerially incised valley(s) features are not observed and is thus not a necessity for submarine fan development.