Shelf-to-basin Floor Architecture of the Rosetta Turbidite System (Western Nile Delta, Egypt)
Sébastien Migeon, Pierrick Rouillard, Elodie Du Fornel, and Jean Mascle
Most recent delta-fed turbidite systems like the Amazon and Indus Fans are classically connected to one mature canyon that deeply incises the continental shelf and slope. In these cases, process of sediment-pathway migration generally occurs at the base of the slope, through channel avulsions. The Mississippi and Bengal Fans are two other cases where migration of the main sediment pathways was documented directly on the upper part of the continental slope. To better constrain processes of construction and evolution of delta-fed turbidite systems, the Rosetta turbidite system (western Nile deep-sea fan) was investigated from the shelf to the basin using multibeam bathymetry, backscatter imagery, 2D and 3D seismic-reflexion data.
The main architectural elements identified on the present-day seafloor and in the Plio-Quaternary sedimentary pile are canyons, mass-transport deposits (MTDs), turbidite channels and turbidite lobes. They have been replaced within a relative chronological framework to build an architectural model. The Rosetta system appears as a rapid point-source migrating system driven by large-scale slope failures and sea-level variations. During falling sea-level stages, sediment transfer is constrained by headwall scars at the shelf break, resulting in the construction of small slope channels on top of MTDs and depositing ponded lobes in topographic lows. Then, a short submarine canyon progressively builds. Eleven diachronous canyons were identified on the outer shelf in an area 55-kilometer wide. In their continuity, channel-levees systems prograde toward the basin floor where they deposit wide distal-lobe complexes. Sea-level lowstands favour the development of wide shelf-margin deltas. They prograde and fill-up the canyon, and cause triggering of MTDs at the shelf break.
This architectural evolution of the western Nile deep-sea fan might be used as a predictive analog for gas reservoirs for the Miocene-Pliocene formations of the Nile margin and, more generally, for any other unconfined delta-fed turbidite systems.
AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013