Extensional Tectonics and Facies Distribution in the Gulf of Suez

R. H. Graham, J. M. Hurst

The Gulf of Suez is an asymmetric Miocene rift 80 km wide in its central part. The main fault blocks of the central sector, Esh El Mellaha and Gebel Zeit, are believed to link into an easterly dipping crustal megashear. A set of antithetic faults in the Gebel Gharamul area mark a change in basin polarity resulting in a transition to westward dipping faults and easterly dipping fault blocks. The region is part of a complex transfer zone that crosses the Gulf between Gebel Gharamul and Belayim.

Asymmetric syn- and post-rift elevation is of two kinds: instantaneous isostatic responses to two major episodes of fault-controlled stretching and an asymmetric regional doming across the Gulf. The western shoulders have been elevated 1.5 km and Sinai has risen 3.5 km, which may be related to ductile stretching displaced from brittle stretching by a crustal megashear.

The pre-rift sequence of the Gulf is characterized by accommodation folding in the hanging wall of curving faults. The most spectacular hanging-wall folds are associated with "scallops" in the footwalls of the main faults along Esh El Mellaha and Gebel Gharamul. The largest faults are relatively planar, but extreme footwall rotation in the Gebel Zeit fault blocks seems incompatible with "domino rotation" and may be due to the deformation of one major fault in the hanging wall of another.

Both carbonate and siliciclastic syn-rift sedimentation patterns are profoundly influenced by faulting. These relationships are clearly seen along Esh El Mellaha, Gebel Gharamul, and Abu Rudeis. Esh El Mellaha is a footwall to a major extensional fault, which looses its displacement to form a flexure southward. Coralgal-rimmed shelves mantle the footwall. Sedimentation began along the southern flexure and prograded over the flexure. Simultaneously, vertically accreting carbonates spread along the main footwall but were precluded from prograding basinward by the fault scarp.

Gebel Gharamul, a horst between synthetic and antithetic faults, forms the locus for a complex carbonate shelf, which developed an eastern coralline rim and prograded down the hanging wall of a growing half-graben. Siliciclastic fan-deltas axially filled the half-graben. Simultaneously, a transfer flexure developed along the northern margin of the horst. Here, a biostromal carbonate shelf mainly vertically accreted but some progradation is recorded by flat-based sigmoidal clinoform units.

Abu Rudeis is a basin located on the footwall to the main eastern basin-bounding fault. Sedimentation was dominantly shallow marine siliciclastics derived axially and laterally, including by erosion of the main footwall crest. Fan deltas prograded laterally through discrete transfer zones along the border fault. Growing synclines, parallel to the main faults, promoted axial fill down the plunge by prograding fan deltas and steeply dipping (20°) progradational units in the lateral fill. In the area of minimal clastic input, a carbonate shelf prograded axially into the basin.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.