Stages of the Structural Evolution of the Red Sea - Gulf of Suez Rift, Egypt

By

 Amgad I. Younes¹, Ken McClay²

(1) Shell Oil Company, Houston, TX (2) Royal Holloway University of London, Egham, Surrey, United Kingdom

 Rift basins are potential oil provinces because they offer the structural and lithologic elements necessary for generation, accumulation and entrapment of oil. Fieldwork in the Red Sea area shows that rifts formation generally evolves through three distinct structural stages. 1) A reactivation stage, where deformation is dominated by reactivation of pre-existing fabric, dismemberment of the crust, and setting up its regional geometry, e.g., the formation of accommodation zones, which are controlled by Precambrian shear zones. Rift shoulders are defined in this stage by exploiting pre-existing fabric resulting in their characteristic zigzag pattern. Minor block rotation and local faulting perpendicular to rift axis occur at this stage. Movement on pre-existing faults controls locations and direction of sediment input points. 2) A linking stage where rift-perpendicular faults propagate along strike linking earlier reactivated faults via a system of relay ramps and transfer faults, which influences deposition of synrift sediments. Further displacement on faults allows fault block rotation and footwall uplift. 3) A mature stage, where the rift fault system reaches its maximum structural development forming through-going, basin-ward coastal faults that are generally perpendicular to the extension direction. Displacement on intra-rift faults increases while extension becomes focused along the rift axis. The rift reaches its greatest depth at this stage and deposition of reservoir-quality synrift sediment is minimal.

In the subsurface, it is expected that fault complexity is higher in blocks bounded by long, rift-perpendicular coastal faults, and that vertical staking position of synrift sediments varies vertically and laterally according to rifting stage.