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 km². 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.