Syn-Rift Carbonate Depositional Patterns: Miocene, Gulf of Suez, Egypt

John M. Hurst

The Suez rift, initiated in the Miocene, consists of asymmetric fault blocks, separated by transfer zones. Syn-rift Miocene carbonates developed on highs; the intricate relations are illustrated at Gebel Gharamul and Esh El Mellaha.

Gebel Gharamul is a rollover, cut by antithetic faults, located on a transfer zone. Small coralgal rimmed shelves initially developed over the eroded footwall nick of an early western antithetic. Steepening depositional dips reflect increasing graben subsidence. Subsequently, the main easterly antithetic regionally lowered the rollover, promoting stacked coral rimmed shelf sequences with increasing dip filling the graben, with the back reef onlapping the main rollover crest. Simultaneously, a low-angle flexure (2°-3°) developed along the northern rollover margin. Low-angle (5°) biostromal rimmed shelves, exhibiting sigmoidal clinoforms rapidly accreted laterally, as reflected in flat-based sequences. Depositional patterns eventually merged over the rollover to produce l terally complex rimmed shelf sequences.

Esh El Mellaha is a footwall to a major extensional fault. In a southerly extensional cusp (20 km), the fault throw decreases from kilometers to flexural (2-3°) displacement. Coralgal rimmed shelves and escarpment fringing reefs mantle the footwall. Initial, thick, and most laterally extensive sequences develop over the flexure. Accretion is primarily subvertical, reflecting continuous flexural subsidence. Where the fault cusp has less than a 30° inclination, carbonate sequences exhibiting oblique and oblique sigmoid clinoforms (40°) prograded over and heeled the fault during periods of fault inactivity. With a fault plane inclination over 40°, slope progradation was precluded and thin vertically accreting escarpment sequences developed.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.