Seismic stratigraphy of giant mass movements, including megaturbidites, on recent continental margins

Transfer of sediments downslope by mass movement processes can be divided into rapid and slow events. The rapid events occur over a few minutes or hours, and the slow events are more continuous and take a longer period of time. Seismic records of rapid mass movement deposits are characterized by a clearly defined continuous shear surface, the lateral limits of which are unconformable, with generally chaotic or transparent internal structures, and an erosional scar. The deposits of slow mass movements are recognized by lack of a clearly defined shear surface, conformity of the lateral limits of those implied shear surfaces, stratified internal structures, stretching of upper sedimentary layers, and lack of an erosional scar. Most of the examples presented in this paper have been selected from seismic surveys conducted in the Mediterranean Sea, especially in the region between the Ebro Delta, on the east coast of Spain and the Gulf of Lion in France.