Developing carbonate platforms: Southern Gulf of Suez, northern Red Sea

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The Ashrafi reef complex represents two small (∼8-10 × ∼2 km) carbonate platforms and associated shoals located along the western side of the Jubal Strait at the Gulf of Suez's southern end. These features are developing in an active marine environment that is operating within the geologic constraints of a tectonic trough characterized by mountainous fault-controlled margins. Origin of the platforms is uncertain, but the present morphology appears to be a product of the dynamic marine setting in which they are developing. Tidal flow between the Red Sea and the Gulf results in strong rectilinear currents (commonly >50 cm s ). Of the current velocities, 5-10 cm s can be attributed to surface currents driven by a regional, unidirectional wind that blows from north to south down the axis of the Gulf throughout the year. Side-scan sonar data, coupled with echo-sounder profiles, direct observations via Scuba, and bottom sampling indicate that the Ashrafi platforms are actively building northward by windward reef accretion and extending to the south by sediment transport and accumulation. The drumstick shape is a product of wave-induced reef development along the northern margin and sediment distribution forced by strong tidal currents, which, coupled with unidirectional wind drift, favors net transport to the south. Small reefs and hard-grounds along the downdrift platform flanks assume a linearity consistent with the long axis of the platform. The intensely mounded sediment of the platform flanks suggests that bioejection of particles in the mound-building process, together with a strong flow field, is a downdrift sediment transport agent. Although the ambient salinity of surrounding Gulf water is ∼41‰, platform-top water masses were measured at >47‰. A lack of significant coral growth on the shallow platform top and the almost total exclusion of sediment-producing calcareous green algae may be related to these hypersaline conditions. Sediments for the platform flanks are largely provided by the breakdown of platform margin reef communities and in-situ organisms (largely foraminifera). © 1984. -1 -1

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Marine Geology

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