From a sedimentological point of view, the continental shelf of the French Guyana can be divided in three parts, parallel to the littoral: (1) the coastal zone where a very fluid mud is found; (2) a large band of sands which covers the rest of the continental shelf; (3) the zone of pelagic muds which corresponds to the lower part of the continental slope. The passage between the sands of the shelf and the littoral or pelagic muds is obtained by the intermediary of the muddy sands.