Middle Pleistocene karst evolution in the state of Qatar, Arabian Gulf

Karst is widespread on the peninsula of Qatar in the Arabian Gulf, including depressions, sinkholes, caves, and solution hollows. More than 9700 large and small depressions, and several exposed sinkholes and caves are known. Field and air-photo studies indicate that the depressions, sinkholes, and caves of Qatar are genetically related, sinkholes representing an early phase in the development of depressions. Karst is concentrated mainly within the limestone, dolomite, gypsum, and anhydrite horizons of the Eocene Rus and Dammam Formations. Most karst features in Qatar show NE-SW and NW-SE orientations, similar to the joint and fracture systems. This observation indicates that rock type and the presence of joints and fractures played a major role in the development of karst in Qatar: Cylindrical, bottle- shaped, compound, and bowl-shaped morphotype karst pits were identified. These forms represent a genetic sequence in which the bowl-shaped pits evolved through a series of cylindrical and bottle-shaped compound intermediate stages. Most karst of central Qatar was formed due to extensive subsurface dissolution of carbonate and sulfate deposits under Middle Pleistocene wet climatic conditions and consequent subsidence. Joint-flow drainage may account for differential dissolution resulting in the formation of a pitted karst terrain in the northern part of Qatar.