GLACIGENIC DEBRIS FLOWS ON THE NORTH-SEA TROUGH MOUTH FAN DURING ICE STREAM MAXIMA

Numerous short sediment cores which penetrate through the glacimarine section and into glacigenic debris flow debrites (GDFs) on the North S ea Fan are investigated. The sampled GDFs represent the uppermost of s everal sequences of these stacked bodies, many hundreds of metres thic k. The GDFs occurred over slopes from 0.3 to 0.7 degrees and examples are found from the shelf break at the mouth of the Norwegian Channel t o the Norway Basin floor, 300 km distant. The GDF diamicts are structu reless and homogeneous in terms of grain size, magnetic susceptibility , NRM, bulk density, water, carbonate, foraminiferal and rock fragment content. This applies both from GDF to GDF across the fan and in a pr oximal/distal sense. Comparison of the investigated lithologic paramet ers with Weichselian till from a borehole in the Norwegian Channel (20 0 km up-ice) shows striking similarity to the GDF debrites. AMS C-14 d ates at the GDF/glacimarine contact and stratigraphic relationships in dicate voluminous deposition before 18 ka, continuing, possibly uninte rrupted, until ca. 16 ka, and a final phase halting just before 15 lia when the Norwegian Channel became ice free. This chronology, the comp arable lithologic character between till and GDF debrites, and a seism ic continuity confirms inferences that the GDFs are directly associate d with glacial ice at the shelf break. The glacial efflux has not been subject to subsequent sorting and the homogeneity of the GDF is thoug ht to reflect thorough mixing in a deforming till layer beneath a fast -flowing ice stream. The glacimarine section subsequent to GDFs shows no indications of turbidity flow. Observations are compatible with a s low, non-disintegrating (cohesive) 'plug' flow transport mechanism wit h little sediment/water interaction on the upper surface. Minor distal differentiation might reflect a change in flow process. Deposition on the fan margins from water-borne glacimarine processes simultaneous w ith GDF deposition is limited. (C) 1998 Elsevier Science B.V. All righ ts reserved.