QUATERNARY REEF TERRACES OF RED SEA COAST,
EGYPT, AND THEIR RELATIONSHIP TO
TECTONICS/EUSTATICS
ABBAS M. MANSOUR
Geology Dept, Fac. Sciences, South Valley Univ., Qena 83511, Egypt.
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Quaternary reef terraces along the Red Sea coast, Egypt, are two to six terraces, three of them can be distinguished in several areas, Each reef unit exhibits a short distance lateral facies development begining at the shore with mainly siliciclastic beach, and ending at the reef zone of carbonate sediments. Reefs with their siliciclastic associations occur in the form of repeated cycles reflecting their tectonic effect and/or sealevel changes. They exhibit different degrees of diagenetic alterations 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. The relative decrease of detrital sediments in the younger reef sequences and the increasing width of these younger reefs toward the sea probably suggest decreasing of the uplift rate of the Red Sea coast.
Pleistocene sequences comprise continental sediments and shallow-water carbonates and siliciclastics of different facies based on field observations, sedimentologic analysis and distribution of fossils, mostly corresponding to those of modern fringing reefs most probably reflecting similar climatic conditions. All reef sequences reveal transgressive phases developed during the sea level rise, while the alluvial deposits are regressive sequences accumulated during the lowering of sea level. Sea level fall caused deposition of large alluvial deposits that buried the pre-existing reefs, also deposition of evaporites in the depressions of the raised beach adjacent to the sea.
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