Rudist

El-Hassana dome is an open museum maintains a full record of ancient life. It is one of the famous and attractive geological sites in Egypt and deserves to be one of the protectorate areas. The Actaeonella-bearing limestone-marl member of Abu Roash formation in El-Hassana dome exhibits a contrasting dark tone relative to the encompassing white cliff forming limestone-dominated members. It consists of shale, marl and limestone that yield in some places Trochactaeon salomonis, Nerinea requieniana, Durania arnaudi and Millestroma nicholsoni. Facies hierarchy at El-Hassana includes: low-energy skeletal floatstone representing initial and start-up stage, rudist/ sponge boundstone of the catch-up and colonization stage, and high-energy bioclastic grainstone representing a cease of mound growth and destructive stage via effective wave and current action. The abrupt development of middle to outer platform argillaceous carbonate facies with local rudist/ sponge mounds of the Actaeonella-bearing limestone member above the inner platform shallower carbonate facies of the underlying "limestone" member may suggest a retrogradation accompanied with a deepening of the depositional accommodation.