The initiation of sliding on the mid Norway margin in the Mّre Basin

The continental slope off Mid Norway is one of the most unstable continental slopes in the world, being the locus for several large mass movements including the important Storegga Slide. Comparatively little is known about the initiation of slope instability in this region. Here 2D and 3D seismic reflection data are used to describe the two earliest slides to occur in the Neogene of the Mّre Basin in order to aid understanding of the initiation of slope instability. The first slide was sourced from the continental slope and occurred sometime between 3.6 Ma and the time of deposition of sediments that failed as the second slide. The second slide was also sourced from the continental slope, and the sediments that failed in this slide were deposited before 1.8 Ma. This second slide is larger in volume than the Storegga Slide. The deposition of the package of sediments that failed in the two slides coincided with the deposition of a large contourite mound in the north of the basin. A polygonal fault system in this basin ceased activity at the time of arrest of an opal A/opal CT boundary. This arrest is linked temporally to the onset of slope instability. The onset and continuation of slope instability on this margin are also linked with a steepening continental slope, due to tilting and subsidence of the margin.