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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 72 (1988)

Issue: 5. (May)

First Page: 555

Last Page: 572

Title: Facies and Geologic History of an Exposed Miocene Rift-Margin Carbonate Platform: Gulf of Suez, Egypt

Author(s): N. P. James (2), M. Coniglio (3), D. M. Aissaoui (4), B. H. Purser (4)


Abu Shaar is a small exhumed carbonate platform of lower to middle Miocene age on a horst of Precambrian crystalline rock along the western side of the Gulf of Suez. The reef-rimmed complex is entirely dolomite but with exquisitely preserved primary and diagenetic microfabrics. Similar platforms, some of which contain hydrocarbons, are buried beneath evaporites in the Gulf.

The platform developed in three stages, defined as local members of the Rudeis Formation. The first stage records deposition during progressive marine onlap as aprons of mixed terrigenous-carbonate sediments evolved into a wide reef-rimmed platform. Synsedimentary platform-margin collapse subsequently removed the most seaward portions of the reefs along the eastern Gulf-facing margin. These truncation surfaces were then covered by a second phase of reef growth and deposition of fore-reef carbonates. The third and final stage, deposited following a sea level drop and subaerial exposure, is a series of well-bedded peritidal carbonates that become progressively more evaporitic upward. Fore-reef facies are again truncated by synsedimentary slope failure. Former evaporites are now recorded as collapse breccias, contorted bedding, black chert nodules, and evaporite molds.

Porosity is mainly secondary as vugs and molds and is highest in platform interior facies. These more porous sediments contained more aragonitic components originally and were less affected by submarine cementation. In contrast, the higher degree of synsedimentary lithification of platform-margin reef and fore-reef sediments is comparable with what is commonly observed in modern reef-dominated platform margins.

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