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The two narrow gulfs of the northern Red Sea, Gulf of Suez and Gulf of Eilat (Aqaba), have had different tectonic histories, but both display active interfingering of siliciclastic and carbonate facies. In an early stage of rifting, these embryonic seas are flanked by rugged mountains (about 2,000 m, 6,500 ft) and narrow coastal plains built of fans composed of poorly sorted terrigenous debris. An arid setting promotes aperiodic transport of siliciclastic sediments as well as deposition of evaporites (coastal sabkhas) and carbonates (reefs and associated sediments). Gulf margins prograde by a combination of rapid fan deposition during flash floods and subsequent carbonate stabilization of terrigenous fans and cones during intervening periods. High-resolution seismic and s de-scan sonar data suggest that narrow pathways for sediment transport are continually active on these features and probably accommodate much of the sediment transport to deep water during small discharge events. Large flash floods may completely overwash carbonates at the distal ends of fans, requiring renewed reef development. Rapid siliciclastic deposition, coupled with biological and chemical binding of carbonates as well as their tendency toward vertical buildups, results in steep slopes along the gulf margins.
The Gulf of Suez is shallow (< 100 m, 330 ft), and a relatively broad (> 12 km, 7.5 mi) and geometrically complicated strait separates it from the northern Red Sea. In contrast, the Gulf of Eilat is deep (< 1,800 m, 5,900 ft) and has a very narrow strait. Although both basins result from rifting associated with opening of the Red Sea, the Gulf of Suez is dominated by normal faults and tilted blocks, whereas the Gulf of Eilat formed primarily by strike-slip displacements with minor movements perpendicular to its extension. Seismic and borehole data confirm that the Gulf of Suez is a graben-like structure that has filled with nearly 6 km (20,000 ft) of dominantly siliciclastic sediment since Miocene times. An evaporite unit over 1-km (3,300-ft) thick and numerous thin carbonate horizons as well as local reef buildups interfinger with the noncarbonates. Over 3 km (9,800 ft) of sediment fill has been confirmed from the Gulf of Eilat, but a base for the sequence has not been identified. Turbidites and pelagic deposits fill the deepest basins.
The Gulf of Suez contains numerous carbonate platforms seated on subtle gulf-parallel structures. Some of these carbonate build-ups suggest that they are the initial stages of much larger carbonate platforms that will develop as rifting continues. Modern physical processes--strong axial winds (< 30 m/sec, 100 ft/sec), an energetic gulf-parallel wave field, and vigorous tidal currents (> 50 cm/sec, 20 in./sec)--tend to streamline reefs and sediment bodies, creating spindle-shaped carbonate platforms. The Gulf of Eilat has no mid-gulf platforms, but a complex of reef-dominated carbonates exists on gulf-normal structural blocks at the Strait of Tiran. A cross section reduction of this already narrow strait by lowering of sea level, reef growth, and/or sedimentation could drasticall change the basin-filling process through restricted flow by eliminating reef growth and initiating salt deposition.
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