Formation of large, crater-like evacuation structures in ooze sediments in the Norwegian Sea. Possible implications for the development of the Storegga Slide

Several crater-like structures, up to 20 km wide and 300 m deep, have been identified by mapping of the top of the Oligocene-Miocene ooze formations in the Norwegian Sea (Fig. 1). The upper part of the ooze has been evacuated from the structures and emplaced in mounded, local accumulations of ooze sediments located stratigraphically above and geographically downslope relative to the evacuated structures. The structures are filled in by mass flow deposits belonging to the Plio-Pleistocene Naust Formation. Our conceptual model implies that the evacuation structures were triggered by mass flows which loaded ooze sediments at the sea floor or at shallow burial. The ooze was evacuated due to its low density which caused it to ascend to the surface of the mass flow.