ORIGIN AND DIAGENESIS OF GEBEL MARYUT CARBONATE SAND RIDGE, WEST OF ALEXANDRIA, EGYPT. ABDEL-MONEIM A. MAHMOUD1, RADWAN A. ABUL-NASR1 and YASSER A. EL SAFORI2 Dept Biological and Geological Sciences, Fac. Education, Ain Shams Univ., Roxy, Cairo, EGYPT 1Dept. Geology, Fac. Science, Ain Shams Univ. Abbassia, Cairo, EGYPT2. The elongate carbonate sand ridge of Maryut lying 21Km west of Alexandria parallel to the seashore about one Km long, 20m high, was sampled for sedimentological and diagenetic studies. Petrographic investigation shows that this carbonate body is of eolianite origin, probably a beach dune. Diagenetically, the lower part of this eolianite carbonate body is affected by stagnant fresh water phreatic diagensis, the middle part by the active fresh water phreatic zone and the upper part by the vadose zone.