Gulf of Suez-Rift Basin Stratigraphy: An Interplay of Subsidence and Eustatic Sea Level

Mark Richardson, Michael A. Arthur

The Gulf of Suez and Red Sea rift basin underwent a period of rapid subsidence from the early Miocene to the Pliocene during which time a thick (up to 4 km) series of marine evaporites accumulated within the basin. The evaporitic sequence interfingers with carbonates and clastics over structural highs within and along the margins of the basin. Evaporite deposition was also interrupted basin wide by short periods of normal marine sedimentation. Timing and paleo-oceanographic aspects of evaporite deposition within the rift is controversial. A changeover of marine source waters within the basin from the Mediterranean Sea to an opening of the rift to the Indian Ocean occurred sometime between the earliest Messinian and earliest Pliocene.

Preliminary data suggests that anhydrites from this evaporite sequence retain original Miocene seawater Sr⁸⁷/Sr⁸⁶ values which can be compared to Neogene strontium isotope versus time curves in order to further constrain the age of the nonfossiliferous evaporite group.

This, combined with currently accepted biostratigraphies for the normal marine strata, enable us to refine rift stratigraphy in order to examine basin subsidence, evaporite accumulation rates, and the correlation of rift tectonics, sedimentation, and associated paleo-oceanographic events. Initial fragmentation and subsidence propagated from the south to the north in the Gulf of Suez during the Aquitanian to Burdigalian (20-25 Ma), and mixed clastic, carbonate, and evaporitic sediments (Nukhul Formation) up to 700 m thick were deposited in isolated subbasins within the rift. This episode was followed by renewed uplift of the rift shoulders, rapid subsidence, and increased clastic influx (late Rudeis Formation) during the Burdigalian (ca. 20-17 Ma). This rapid subsidence, accompanied by deposition of mixed carbonates, clastics, and evaporites (Kareem and Belayim Formations), continued through the Serravalian (17-11 Ma). Rapid subsidence persisted during Tortonian-Messinian time (11-5 Ma) when the major marine evaporites were deposited (South Gharib and Zeit Formations). Subsidence rates decreased somewhat during the Pliocene-Quaternary, accompanied by uplift of rift shoulders and deposition of thick clastic wedges along the flanks of the rift. Isolated subbasins continued to accumulate mixed marine evaporite-clastic facies (Shukheir Formation).

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