CONTRIBUTION TO DEPOSITIONAL ENVIRONMENTS OF THE DUWI FORMATION (UPPER CRETACEOUS) EAST WADI QENA-NILE VALLEY, EGYPT ESSAM M. EL KHORIBY Geol. Dept, Fac. Sci., El Mansoura Univ., Egypt The Upper Cretaceous rocks of the Duwi Formation exposed at Wadi Hamama and Gabel Abu Had areas, Eastern Desert Egypt, are examined petrographically, mineralogically, geochemically and diagenetically for interpretation of their depositional environments. The Duwi Formation is composed mainly of shales, clastic phosphorites, sandstones and marls with a minor carbonate rocks (limestone and dolostone) and cherts. Several microfacies have been recognized. The clastic phosphatic particles consist mainly of peloids, bone fragments, teeth with a subordinate amount of lithoclasts and coprolites. Francolite is the essential phosphatic mineral identified. The non-clay minerals determined by x-ray analysis include quartz, calcite, dolomite, pyrite, hematite and glauconite. Smectite and kaolinite with a little of illite are the clay minerals identified in the argillaceous rocks. The Duwi Formation is lithologically subdivided into three sub-units; lower, middle and upper Duwi. Each has its own sedimentological characteristics. The phosphatic rocks are generally of low grade. This is due to its lower content of P2O5 and presence of the gangue minerals such as calcite, quartz, hematite and anhydrite. The R-mode analysis of major and trace elements shows that the francolite, organic matter and clastics are mainly responsible for the accumulation of the trace elements encountered in the studied rocks. The diagenetic processes affecting the Duwi Formation sediments include cementation, silicification, glauconization, pyritization, dolomitization, neomorphism, chertification, ferrugination, dehydration and compaction. Several submergence clastic and clastic-carbonate sedimentary cycles have been recognized. These sedimentary cycles show that the climatic changes, sea level oscillations, tectonics and rate of sediment supply played an important role in deposition of the different rocks of the Duwi Formation. The results achieved favour the assumption that the Duwi Formation rocks have been deposited under relatively deep to shallow marine, lagoonal and fluviomarine environments. Reworking and transportation processes possibly led to the accumulation and concentration of phosphates under well-aerated, agitated water conditions. A depositional and diagenetic model for the studied rocks of the Duwi Formation is proposed.