Mass-Wasting Events, Gravity Flows, and Their Impact on Channel Migration and Lobe Construction: An Example from the Nile Deep-Sea Fan, Oriental Mediterranean

Migeon, Sebastien¹, Lies Loncke², Emmanuelle Ducassou³, S.ébastien Garziglia¹, Jean Mascle¹, Eliane Gonthier⁴, Thierry Mulder⁴ (1) UMR Geosciences Azur, Villefranche sur Mer, France (2) Université de Picardie, Amiens, France (3) Université Bordeaux 1, Bordeaux, France (4) Université Bordeaux1, Talence, France

Gravity flows and mass-wasting events are major factors controlling the development of turbidite systems on continental slopes and rises. They control the location and construc­tion of potential sedimentary traps for hydrocarbon, and also participate in geohazards along continental margins. The Nile deep-sea fan is a wonderful natural laboratory allowing the study of triggering mechanisms of gravity flows and landslides, and their impact on the evo­lution of channels and lobes. In the western part of the Nile deep-sea fan, silico-clastic and carbonate supply allowed construction of the Rosetta turbidite system. It consists of three main sedimentary piles that gradually shifted southwestward. Within each pile, several meandering channels migrated toward the deep basin through successive avulsions. Flow by-passing was a common phenomenon along the channels, allowing the construction of large lobes clearly identified on the backscatter imagery. Individual lobes are 100-km long and 30-km wide, and exhibit a complex morphology with small secondary channels. Cores revealed deposition of interbedded sandy turbidites and thick debris-flow deposits. Six fail­ures (volume > 5 km3) affected the upper slope, east of the Rosetta canyon. The scar observed now is 50-km long and 200-m height. On the slope, failures partly covered some channel-levee systems, suggesting they could be responsible for their gradual southwest­ward migration. Cores 40-m long collected in the youngest failure exhibit deposits tilted by 45° and affected by microfaults. Failures probably result from rapid sea-level drops desta­bilizing under-consolidated sediments. Tri-axial analyses and Morh-Coulomb models provid­ed new insights in the physical mechanism of failure triggering.