Pleistocene development of the SE Nordic Seas margin

Throughout the Pleistocene the sedimentary environment on the SE Nordic Seas continental slope/outer shelf, off western Norway, has been strongly controlled by variability in the Norwegian Atlantic Current (NwAC), glaciations of the shelf areas and sea level changes. Acoustic and core data from the southern Vّring Plateau show a Pleistocene sequence characterised by hemipelagic sediments interfingered by diamictons on the upper slope. The area of the 7.25 14C ka BP Storegga Slide shows evidence of a long history of Pleistocene mega-slides. During the last interglacial, and most likely also during previous interglacials, the slide region has been the locus of rapid deposition between water depths of 800 and 1200 m, as a result of NwAC winnowing along the upper slope. The North Sea Fan region is strongly influenced by glacigenic debris flows (GDFs) deposited during glacial advances reaching the shelf edge, when the Norwegian Channel was occupied by the Norwegian Channel Ice Stream. It appears that GDF activity was initiated at ca. Marine Isotope Stage 12. Interbedded between the debris flow sequences, mega-slide events such as the Mّre and Tampen slides have been identified. During glaciations, when the entire SE Nordic Seas continental shelf was covered by extensive grounded ice sheets, basal till were transported to the shelf edge from where subsequent mass movement occurred. During late glaciation/early deglaciation meltwater plumes were released at the time of disintegration of ice streams in the Norwegian Channel, as is evidenced from the last deglaciation of the margin at ca. 15 14C ka BP. The plume material was transported northwards by currents, before rapidly deposited as a thick package within the Storegga Slide area and on the south Vّring Plateau. Based on identification and dating of iceberg scourings, glacial erosion surfaces and delta deposits on the shelf, subsidence rates between 0.7 and 1.2 m/ky have been calculated for the last ca. 250 ka.