GENICULATE CORALLINE ALGAE FROM THE PLIOCENE SHAGRA FORMATION AT WADI ABU DABBAB, MARSA, ALAM AREA, RED SEA COASTAL PLAIN, EGYPT

Abstract: The Pliocene succession in Wadi Abu Dabbab, Marsa Alam area, Red Sea coastal plain is litohstratigraphically subdivided into Gabir, Shagra and Samadai formations in addition to the Pleistocene raised beaches and coral reefs. Lithostratigraphically, in Wadi Abu Dabbab that represents the main investigated section where the Shagra Formation unconformably overlies the Pliocene Gabir Formation and unconformably underlies the Samadai Formation (Plio-Pleistocene age) and represented by mixed siliciclastics and carbonates succession. This formation is highly fossilifrous with coralline red algae in form of erect, in situ crusts, rhodoliths, as well as fragments and corals, bivalved shell fragments, bryozoans, large benthonic and palnktonic foraminifera. The coralline red algae and foraminifera are important constituents of Shagra Formation and highly abundant. This carbonate facies is dominated by different assemblage of coralline red algae in the forms of geniculated and nongeniculated coralline algae. The coralline algal limestone of Shagra Formation contains well preserved geniculate coralline algal species of genus Amphiroa that represents the main target of this study. The systematic study and the taxonomic investigations carried out on the coralline red algae led to the recognition of eleven geniculated coralline algal species that described for the first time in the studied area. The present paper documents eight coralline algal species of genus Amphiroa namely Amphiroa anchiverricosa, A. ephedraea, A. fortis, A. fragilissima, A. prefragilissima, A. prerigida, A. rigida, A. tani, and one new species Amphiroa dabbabensis Hamad for the first time as well as Corallina p r i s c a , Jania guamensis, Subterraniphyllum sp.. The present geniculate coralline algal assemblage is associated with the nongeniculated and dasycladalean algae, this association points that the coralline algal reefal limestone of the Shagra Formation was deposited in the intertidal to shallow subtidal environments at a depth of 10-3 0 m in a shallow warm marine water environments under low energy conditions favorable for reefal growth and rhodoliths formation. The fossiliferous arkoses and conglomerates, alternating with the coralline algal limestone of Shagra and Samadai formations, were derived from the nearby Precambrian basement, transported by streams during short-lived pluvialepisodes and deposited in a very shallow intertidal- beach environment