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Respective contributions of tectonic and gravity‐driven processes on the structural pattern in the Eastern Nile deep‐sea fan: insights from physical experiments

In the Nile deep‐sea fan, thin‐skinned deformation detaching on a layer of Messinian salt has generated an upslope to downslope progression from growth faults, to polygonal minibasins bounded by salt ridges, to buckle folds. Such progression is common in salt‐bearing passive margins, where gravity spreading of the salt–sediment system causes proximal thin‐skinned extension on the shelf and upper slope, and distal contraction along and in front of the lower slope. In the Eastern Nile deep‐sea fan, this structural progression seems to be restricted to a corridor bounded by NW–SE‐trending lineaments more than 200 km in length. These are associated with salt ridges and record strike–slip movements. In the absence of a large grid of deep‐penetrating seismic data accurately imaging the basement, different likely hypotheses have been advanced about the origin of this corridor: (1) it may result from possible deep‐seated tectonics related to the Rift of Suez, combined with salt‐related deformation or, (2) by complex interaction between the overburden's gravity spreading and pre‐existing pre‐Messinian paleo‐topographic features, particularly the possible buttressing effect of a seamount located North of the eastern Nile deep‐sea fan. In order to understand how this corridor could have been generated, we used a series of physical experiments to test the effect on three‐dimensional spreading of a sediment lobe of the following parameters: (1) active, crustal, oblique extension, (2) a dormant subsalt graben, (3) a passive buttress, such as a seamount and (4) complex paleo‐topographic features along the Egyptian margin affecting initial salt distribution. These experiments show that the presence of a distal buttress, combined with a complex Messinian topography best explain the complex deformational pattern observed in the eastern Nile deep‐sea fan.