Abstract Megabeds are thick sedimentary layers extending over thousands of square kilometres in deep-sea basins and are thought to result from large slope failures triggered by major external events. Such deposits have been found in at least three areas of the Mediterranean Sea. Although their discovery dates back to the early 1980s, many questions remain concerning their initiation, source area, extent and the nature of their emplacement. One of the largest previously documented megabeds was emplaced during the Last Glacial Maximum across the Balearic Abyssal Plain, with a thickness of 8–10 m in water depths of up to 2800 m. New 3.5 kHz sub-bottom profiles and sediment cores provide greater constraints on the lateral variability of the megabed and allow it to be mapped beyond previous estimates, with a revised areal extent of 90 000–100 000 km 2 . The megabed terminations show a gradual pinchout to the west and an abrupt eastward termination against the steep Sardinia margin. The megabed presents, in seismic profiles and sediment cores, a tripartite subdivision, which most likely corresponds to the changes in flow regimes across the basin, with a central area of sandy facies and an erosional base oriented NNE–SSW; this allows renewed discussions about the sources and triggers of the megabed.

Abstract The Gulf of Lions presents recurring mass-transport deposits (MTDs) within the Plio-Quaternary sediments, suggesting a long history of mass movements. The two large, surficial MTDs are located on the eastern and western levee of the Rhone canyon over an area exceeding 6000 km 2 and volumes exceeding 100 km 3 . Both MTDs were emplaced 21 ka ago (peak of the Last Glacial Maximum), suggesting a common trigger. Here, we present a multidisciplinary high-resolution geophysical, sedimentological and in-situ geotechnical study of the source and deposit areas of both MTDs to characterize distinct expressions of sediment deformation as well as their spatial and chronological distributions. We show the internal structure of mass movements and resulting MTDs with unprecedented details that were previously represented in the conventional seismic data as transparent and chaotic facies. The combination of multidisciplinary approaches shows new insights into the nature of basal surfaces of the slope failures. In particular, we show that the basal surfaces of the failures consist of clay-rich material contrasting with the overlying turbiditic deposits, suggesting that a strong lithological heterogeneity exists within the strata. We suggest that this change in lithology between clay-rich sediments and turbiditic sequences most likely controls the localization of weak layers and landslide basal surfaces.

Abstract Understanding the genesis of the very peculiar 600 km-wide Santos Basin–São Paulo Plateau system and its narrow conjugate Namibe Margin is a kinematic and structural problem. Several hypotheses have been proposed in order to explain the genesis of this system that imply the same amount of horizontal movement. We investigate the consequences of the horizontal movement in the Santos Basin, based in plate kinematic reconstructions. The kinematic history of this system that we present here, based on the interpretation of seismic profiles and kinematic constraints, has the following consequences: (1) there is no evidence of a ridge jump sensu stricto but, rather, a southwards propagation in the Central Segment of the South Atlantic that starts in the northern part, between the NE Brazilian and Gabonese margins; (2) the Namibe margin evolved as a transform passive margin; (3) the opening direction of the Santos Basin–São Paulo Plateau system is oblique to the general opening motions of the South American and African plates; and (4) this opening is younger (6 Ma) than those of the other basins of the Central Segment of the South Atlantic.