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length the Red Sea is characterized by large areas of vigorously growing corals on fringing andbarrier reefs (CROSSLAND, 1939).In coral reefs, carbonate is deposited as both the reef framework and unconsolidatedsediments. In terms of total carbonate production, the unconsolidated sediments produced by reefsappear to be far more important than the carbonate incorporated in the reef itself (STODDART, 1969;MILLIMAN, 1974). Because of the generally high wave energies, unconsolidated reef Sediments aremostly composed of sand and gravel; silt and clay usually constitute less than 1-295 of the totalcarbonate (MILLIMAN, 1974).Geological studies of coral reefs in the northern Red Sea started about one hundred yearsago, but reefal sediments have been studied in this area for only about forty years. Modem andPleistocene reefs of the south Sinai Peninsula were investigated by WALTHER (1888), HUME(1906), CROSSLAND (1939) and GUILCHER (1979). In Aqaba, RUPPEL (1829), WALTHER(1888), HUME (1906), FRIEDMAN (1966, 1968), MERGNER (1971), MERGNER andSCHUMACHER (1974), GVIRTZMAN et al. (1977), SNEH and FRIEDMAN (1980) andBOUCHOJ et al. (1981) likewise described coral reefs.Texture and Distribution:Red Sea reefal sediments are generally composed from debris of corals and coralline algae aswell as mollusks, echinoderms and foraminifera.In Aqaba, the composition of particles differs spatially: The sands surrounding patch reefsare composed almost entirely of skeletal debris, including fragments of corals, crustose corallinealgae, gastropods, and pelecypods, together with foraminifera tests, small pelecypod shells, echinoidplates and spines (FRIEDMAN, 1968). GABRIE and MONTAGGIONI (1982) recognized eightsediment facies in Gulf of Aqaba reef sediments based on the total component composition andforaminiferal assemblages; four sediment facies were recognized using grain-size data only.Well-sorted, fine to medium, quartzofeldspathic sands (terrigenous facies) occur on beaches and outersandy slopes near wadi mouths. Back-reef areas exhibit relatively well-sorted fine sands ofterrigenous origin, coral and Milliolidae-Soritidae facies. Poorly sorted coral sands, and coralcorallinealgal and Homotremid facies characterize the reef flat and the upper parts of coral-built forereef areas, which respectively display an Amphistegina-Spirolina subfacies and an Acerrulina one.Poorly sorted medium sands of coral-molluscan-foraminiferal facies are restricted to the lower partsof the fore reef zone.In Al-Ghardaqa area (Fig. 3, the coastal sediments are generally coarse, well-sorted, angularto sub-angular arkosic sands mixed with common rock-forming detritus from surroundingformations. These sands are mixed with significant amounts of biogenous fragments. Sediments inthe intertidal zone are much finer and rich in carbonates. The lagoon is also covered by fine carbonatedeposits mixed with reef fragments (EL-SAYED and HOSNY, 1980; EL-SAYED, 1984).Considerable quantities of insoluble residues characterize both Aqaba and Ghardaqasediments (FRIEDMAN, 1968 and EL-SAYED, 1984). The insoluble residue includes quartz andfeldspar grains as well as chlorite, kaolinite and illite. In Aqaba the terrigenous debris is derived fromthe local Precambrian rocks, while in Al-Ghardaqa it originates from the surrounding Neogeneformations.Geochemistry:Little information is available on the elemental composition of reefal sediments from thenorthern Red Sea. Owing to the admixture terrigenous and bioclastic constituents, the chemicalconstituents vary considerably with locality (EL-SAYED, 1984).The average chemical composition of the reefal sediments of Aqaba and Al-Ghardaqa is listedin Table 1. High positive correlation values are obtained between F%03 vs MnO; CaO vs MgO; SrOvs CaO and MgO for most of the reef sediments in the northern Red Sea (EL-SAYED, 1984). Theaverage concentrations of some heavy metals (Fe, Mn, Cu, Zn and Cd) in the reefal sediments areshown in Table 2.344