Analysis of Sediment-Transfer Processes and Deposits in the Eastern Nile Deep-Sea Fan and Levantine Province Combining Seafloor Studies and Reflection Seismics

Galbiati, Mauro ¹; Joanne, Cathy ²; Mascle, Jean ²; Migeon, Sebastién ²; Rocchini, Patrizia ¹
(1) eni e&p, San Donato Milanese, Italy. (2) Geosciences Azur, Nice, France.

In the Eastern Nile Deep-Sea Fan active salt-tectonics induces important seafloor deformation that controls the location of turbidite bodies and the evolution of the channelized system. We studied a geophysical dataset extending from the onshore Delta to the Levantine Basin, including sea bottom morphology and backscatter, sediment cores and 3D reflection surveys, to analyze the recent evolution and mechanisms of the sedimentary transfer. Seismic and multibeam data testify a long-term interaction between sediment transfer and salt-tectonic activity suggesting an eastward migration of the channelized system, partly triggered by climatic changes and variations in the structure and discharge of the Damietta branch of the delta. Sediment transfer and deposition change along slope according to tectonic variations. On the upper slope, regional faults create a system of anastomosed micro-basins. Sediment flux is discontinuous and depends on the filling of microbasins, involving successive flow ponding (infilling), stripping (sediment sorting and overflowing) and bypass (transfer towards other micro-basins). Connection between microbasins is maintained by channels that incise fault scarps or are constructed on top of basins. On the middle slope, channels are guided along axes of subsidence or reliefs and turbidites bodies settle in depressions induced by tectonic forcing. Seismic data reveal numerous large-scale mass-transport deposits that were destructive for the channelized systems, although sand bodies have been preserved in grabens. On the lower slope, channels terminate either in an area of well-developed pressure ridges and salt domes or at the foot of the Erathostenes Seamount. Sandy lobes nestled in confined areas are intercalated with MTDs. Fluid escape features at different scales (mud volcanoes to pockmarks) have also been analyzed. Plio-Pleistocene channelized turbidites in the central Fan and in ponded basins in the Eastern domain, are targets for gas exploration. In the Eastern province, structurally bounded sub-basins off the slope break, collecting sands from the shelf edge, have been active since the Middle Pliocene. In the central section, erosive leveed channels cut the entire slope. In buried sequences geological processes are still to be fully understood, seismic indications are poorer and tectonic control on sedimentation stronger. Exploration and development can be supported by knowledge of the evolution of the system in its recent stages.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.