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Contourite features are increasingly identified in seismic data, but the mechanisms controlling their evolution remain poorly understood. Using 2D multichannel reflection seismic and well data, this study describes large Oligocene- to middle Miocene-aged sedimentary bodies that show prominent lateral migration along the base of the Argentine slope. These form part of a contourite depositional system with four morphological elements: a plastered drift, a contourite channel, an asymmetric mounded drift, and an erosive surface. The features appear within four seismic units (SU1–SU4) bounded by discontinuities. Their sedimentary stacking patterns indicate three evolutionary stages: an onset stage (I) (~ 34–25 Ma), a growth stage (II) (~ 25–14 Ma), and (III) a burial stage (< 14 Ma). The system reveals that lateral migration of large sedimentary bodies is not only confined to shallow or littoral marine environments and demonstrates how bottom currents and secondary oceanographic processes influence contourite morphologies. Two cores of a single water mass, in this case, the Antarctic Bottom Water and its upper interface, may drive upslope migration of asymmetric mounded drifts. Seismic images also show evidence of recirculating bottom currents which have modulated the system’s evolution. Elucidation of these novel processes will enhance basin analysis and palaeoceanographic reconstructions.

Numerous bottom current-controlled depositional and erosional features, which together form Contourite Depositional Systems (CDS), have been recognized in deep-water settings over the past decade. Most of these systems are described based on two-dimensional (2D) seismic data, whereas only a few CDS have been characterised from high-resolution 3D data. Here we document a newly identified CDS that formed during the Paleocene within the Morondava Basin, offshore west Madagascar, through analysis of a depth-migrated 3D seismic survey, enhanced by the implementation of seismic attributes. Three seismic units (SU) mark the main evolutionary stages of the CDS: (a) the onset (SU1), (b) drift growth (SU2), and (c) burial (SU3) stages. The growth stage documents lateral upslope migration of a mounded drift and its associated moat. The increasing, long-term influence of bottom currents along the foot of the slope occurred simultaneously with plate tectonic, climatic and oceanographic changes. Evidence amassed from the CDS highly erosive bounding discontinuities, internal discontinuities, and moat architecture all indicate the intermittent behaviour of the currents over shorter time frames during its formation. Drift deposits form under the influence of weaker currents, while discontinuities appear to record the most vigorous currents, producing the large-scale morphology of the system.