The tectono-sedimentary evolution of a rift margin carbonate platform: Abu Shaar, Gulf of Suez, Egypt

N E Cross, B H Purser, Daniel Bosence

Research output: Chapter in Book/Report/Conference proceedingChapter


Abu Shaar is a dolomitized Miocene, mixed carbonate- siliclastic platform outcropping on the crest of a fault block in the south-western margin of the Gulf of Suez, Egypt. The Miocene platform rests unconformably on Precambrian basement and is cut to the east by a basinward-dipping and throwing extensional fault; Miocene strata are tilted to the western margin of the basin. Up-section decreases in dip, successive westward thickening of strata and onlap of beds on the hangingwall dip slope indicate that fault-block rotation occurred before and during deposition of this Langhian-aged syn-rift platform.

Miocene depositional morphology has been exhumed by Quaternary erosion to reveal platform-margin buildups and slopes in the footwall, and gently sloping open-marine to restricted-marine platform-top facies in the hangingwall dip slope. Hangingwall areas are characterized by coarse, shallow marine sandstones derived from exposed basement of the northern Esh el Mellaha fault block and the basin margin Red Sea Hills. The southern margin passes into a transfer zone. The last Miocene carbonates to be deposited on the platform- top are restricted marine carbonates and signal the onset of evaporative conditions in the Gulf.

The large, three-dimensional exposures of Abu Shaar have enabled the recognition and platform-wide correlation of nine depositional sequences which provide a spatial and temporal framework for syn-rift platform evolution. Three depositional sequences show evidence of syndepositional fault-block rotation with synchronous footwall uplift, and erosion and hangingwall deepening and flooding. These depositional sequences are characterized by thickening down the hangingwall ramp, onlap on to the hangingwall and footwall unconformities overlain by aggradational shelf-margin reefs and steep slopes off the footwall block. Where fault throw reduces into the transfer zone, footwall uplift is less, slopes are less steep, and shelf-margin reefs are thicker and more progradational. Two depositional sequences have platform-wide occurrence but show no thickness changes and are interpreted to result from regional (tectonic or eustatic) sea-level changes. Two other depositional sequences are restricted to the steep slopes of the footwall margin and are generated by submarine fault-related, scarp retreat. They are down- lapping wedge-shaped sequences in which shelf-margin reefs pass down-dip into slope deposits. They do not have equivalents in the transfer zone margin or the hangingwall and therefore are not generated by fault- block rotation.

Facies models are proposed for the footwall and hangingwall regions of the platform and comparisons are made with other tilt-block carbonate platforms.
Original languageEnglish
Title of host publicationSedimentation and Tectonics in Rift Basins
Subtitle of host publicationRed Sea:- Gulf of Aden
EditorsBruce H Purser, Dan W J Bosence
Number of pages25
ISBN (Electronic)978-94-011-4930-3
ISBN (Print)978-94-010-6068-4
Publication statusPublished - 1998

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