THE FORALGAL CRUST FACIES OF THE DEEPER FORE REEFS IN THE RED-SEA - A DEEP DIVING SURVEY BY SUBMERSIBLE

Autochthonous organic frameworks from the deeper fore reef (-50 m to -110 m) of the Red Sea are composed predominantly of incrusting calcareous red algae and foraminifera. This foralgal crust facies is represented by three types. The first is a pure foralgal crust community which forms small buildups with bumpy surfaces. Calcareous red algae and incrusting formainifera comprise more than 60 % of the biogenous fabric. The second type is a framework in which foralgal crusts are secondary binders around the hermatypic deep water scleractinian Leptoseris fragilis. The third type occurs on drowned reefs, exhibiting a mixture of Pleistocene shallow water and present day deep water binding species. Therefore, the morphology of this subfacies is more governed by an inherited relief, characterized by pinnacles and barrel shaped towers. This present day deep water foralgal community started to develop within the Cretaceous in shallow water environments, composed predominantly of corallinaceans, peyssonneliaceans, and subordinately of acervulinid foraminifera. With the beginning of the Neogene, the shallow water community of reef binding foraminifera and calcareous algae changed and become dominated by the foraminifera Acervulina. The living foralgal crusts of the deeper fore reef in the Red Sea represent a binding community of Upper Cretaceous and Palaeogene shallow water environments which has shifted in greater water depth with time. © 1990.