Structure and Evolution of a Fault Degradation Complex, Coastal Fault Belt, Suez Rift, Egypt

Muravchik, Martin; Gawthorpe, Rob; Sharp, Ian

Fault degradation complexes constitute spectacular structures originated by gravity sliding and slumping of blocks due to instability of large fault scarps. They are a very common phenomena in extensional basins, and understanding their complexity is important for maximizing recovery from mature tilted fault block traps in many rift basins. Furthermore, redeposited sediments derived from the breakup of these complexes form potential syn-rift reservoirs adding new reserves to existing fields. Excellent exposures along the Coastal Fault Belt (CFB) next to the El Qaa Fault Block, Suez Rift, Sinai, Egypt, allow for detailed investigation of the coupled evolution of structures and sedimentation in a fault degradation complex.

The present case study extends for approximately 1.5 km into the hangingwall of the CFB and 4 km along strike. It consists in a series of small scale fault blocks (~100's m) composed of both pre-rift and syn-rift lithologies, linked to a basal detachment that is subsequently connected to the CFB. This detachment is developed within an interval of mechanically weak, mixed-facies dominated unit, separating sandstones from competent carbonate rocks above in the pre-rift succession. The syn-rift deposits in the fault degradation complex show a sharp passage from coarse-grained bioclastic deposits at its base into a thick succession of mudstones punctuated by very well sorted sandstones and very coarse-grained conglomerate lobes and lenses. These coarser-grained units composition is dominated by both pre-rift carbonates and syn-rift carbonates of coral origin. Overall, the depositional environment evolved from shallow marine to hemipelagic conditions in a high-gradient area which allowed for the triggering and deposition of turbidity currents, debris flows and rock avalanches.

Structural and sedimentary analysis of the area reveals the existence of several events of gravitational instability preserved in the syn-rift succession, interpreted as previous to the main gravitational collapse event that originated the current fault degradation complex. It is proposed that the triggering of this larger-scale event was caused due to the nucleation of the displacement along the present day CFB.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013