Raised Coral Reefs and Sediments in the Coastal Area of the Red Sea

Abstract

Along the Red Sea, narrow coastal plains ascend directly into fault-bounded blocks within a few kilometers of the shoreline. Littoral areas on both sides of the Red Sea are characterized by mixed sedimentation relating to a complex system of fringing and barrier reefs and alluvial fans. These marine sediments are uplifted to altitudes rarely exceeding 50 m. However, although terraces are well developed on both sides of the basin there is no apparent correlation, the possible exception being the youngest level situated about 2 m above present sea level. Raised coral reefs result from either the corrosive action of waves or from local erosion by occasional torrents creating low cliffs and exposures just above high-tide level. Each reef unit exhibits in a short distance lateral facies changes, which begin at the shore with the beach facies, mainly composed of siliciclastics, and end at the reef crest zone with transition to the fore slope made up of carbonate sediments. A strong similarity can be noticed between sedimentary facies of ancient Pleistocene sediments and those now present in modern fringing reefs. Reefs with their siliciclastic associations occur in the form of repeated cycles reflecting tectonic effects and/or sea level changes. Reef sequences exhibit different degrees of diagenetic alteration, which are reflected by a gradual change of skeletal particles and the early-formed cement, from aragonite and high Mg-calcite to low Mg-calcite. Tectonism controls the areal distribution of the depositional systems and influences the number, thickness, extension, and elevations of the reef sequences. Each sequence in each area can be uniquely correlated to the overall (global) population of dated terraces. Coastal areas of the Red Sea are under stress from a variety of human activities and many have experienced widespread degradation, especially around Hurghada and Jeddah. Hotel, resort and other developments along the coast of Egypt are growing rapidly, destroying raised reefs and threatening valuable coral reef ecosystems. Some areas along the coast suffer from construction problems that are associated with coral reefs. These problems include ground settlement and low bearing capacity which are mainly due to the low shear resistance and high porosity of reef sediments. These problems greatly affect the safe and economic land utilization of the coasts. Prediction of the future changes along the Red Sea coast would give guide lines to what will happen due to the varying nature of the coast. Such predictions would have implications for future social and economic development along the coast. Effective and integrated coastal zone management programs are critical to sustaining the natural resources of the Red Sea.