Miocene Synrift Paleokarst and Related Sulphur Deposit in Gemsa Area, Red Sea Coastal Zone, Egypt

By

 Ali Abdel-Motelib¹, Abdel-Hamid El-Manawi¹

(1) Cairo University, Faculty of Science, Geology Department, Giza, Egypt

Two paleokarst profiles developed within the Miocene sediments of Gemsa area, Red Sea, Egypt. These two-karst systems are separated by erosion surface. The lower is Endo-paleokarst of Upper Miocene, developed mainly in the Miocene gypsum, anhydrite and carbonate of Gemsa Formation. The upper surficial paleokarst is subsequently developed on the overlying carbonate rocks. The erosional contact between the recognized paleokarst profiles is dominated by rhizocretional horizon consists of argillaceous debris and residual organic materials accumulated pedogenetically on the surface and converted onto kaolinite. The lower paleokarst is resulted from ascending hot spring water that intrude the fracture system prevailing during the late Miocene synrift activity of the Red Sea, and may be associated with the processes of oil migration during release of the associated water under relatively phreatic conditions. The upper surficial karst profile is related mainly to a humid paleoclimate of the Quaternary age. Abundant cavities detected in the vicinity of sulfur deposits can be formed by thermal karstification, which is one of the most important processes controlling the formation and redistribution of the sulfur deposits in Gemsa area. The occasional presence of silicification is a rather good indication for thermal karstification processes. A new karst model for the formation of sulfur deposits is suggested. It agrees with the hydrogeological features of the Miocene sequence and its tectonic instability and the numerous intervening unconformity surfaces with the biogeochemical mechanisms of sulfur origin in moderate temperature diagenetic environments.