QUATERNARY SEISMIC STRATIGRAPHY OF THE NORTH-SEA FAN - GLACIALLY-FED GRAVITY FLOW APRONS, HEMIPELAGIC SEDIMENTS, AND LARGE SUBMARINE SLIDES

Approximately 1000 km of high resolution sleeve-gun array transects on the North Sea Fan, located at the mouth of the Norwegian Channel, rev eal three dominant styles of sedimentation within a thick (>900 m) Qua ternary sediment wedge comprising numerous sequences. These are interp reted as: terrigenous hemipelagic sedimentation, large scale translati onal slides, and aprons of glaciogenic debris flow deposits contributi ng to considerable fan construction. Four large, buried translational slides involved sediment volumes upwards of 3000 km(3) each and preced ed the similarly dimensioned ''first'' Storegga Slide on the NE fan fl ank. Several thick (>100 m) terrigenous hemipelagic deposits apparentl y represent long-lived (150-200 kyr) periods of sedimentation whose di stribution indicates fan input via the Norwegian Channel. The upper se quences are each made up of one or several thick (> 100 m) aprons comp rising stacked lensoid and/or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness. They characterize debris flows attributed to periodic input from several phases of a Norwegian Channe l ice stream reaching the shelf edge. Subsidence in the outer Norwegia n Channel allowed preservation of several glaciation cycles represente d by sheet erosion-bounded tills and progradational units. Much of the shelf/slope transition has been preserved, allowing a preliminary chr onology of the fan sequences through correlation with borehole sedimen ts in the Norwegian Channel. Debris flows, which signal the initial sh elf-edge glaciation, are not recognized from the initial glaciation in the Channel (>1.1 Myr) but are associated with a Middle Pleistocene a nd all following glacial erosion surfaces (GES) in the outer Norwegian Channel. This was followed by six further sequences, probably totalli ng over 13,000 km(3) of sediment. At least four of these were shelf-ed ge ice-maximum events the last of which was Late Weichselian age (C-14 AMS). Considering earlier glaciation-related hemipelagic sedimentatio n, material since removed by the large slides, and extensive unmapped areas, total Quaternary fan sedimentation was in the vicinity of 20,00 0 km(3).