The Western Rub' Al-Khali Infracambrian Graben System

ABSTRACT A major Infracambrian graben system is observed along regional seismic reflection profiles in the Western Rub' Al-Khali of Saudi Arabia. This graben system was formed coincident with the development of salt basins in Oman and the Arabian Gulf, and the Najd fault system of the Arabian Shield. Evident structural elements include the northwest-southeast trending Najd faults, and the more commonly recognized north-south trends. The sediments deposited in the grabens can be divided into three units based on seismic character. The inferred basal unit is relatively free of seismic reflections and has an indefinite basal seismic reflector. The middle unit contains parallel seismic reflections marked by high comparative amplitude and continuity. The upper unit represents an eroded wedge characterized by low internal seismic reflectivity. The three units are correlated with the Infracambrian Huqf Group of Oman and the Jubaylah Group of the Najd system of the Arabian Shield. Specifically, the basal unit is interpreted to correspond to the coarse clastics of the Abu Mahara. Formation at the base of the Huqf Group and the Robutain Formation of the Jubaylah Group. The middle seismic unit is interpreted as carbonates and marine clastics, equivalent to the Khufai, Shuram, and Buah Formations of the Huqf Group and the Muraykhah Formation of the Jubaylah Group. The upper seismic unit is interpreted as the clastic facies equivalent of the Ara Formation salt of the Huqf Group. The carbonates of the Huqf Group of Oman are the proven source rocks of oil fields in the Ghaba and South Oman Salt Basins, and therefore the middle seismic unit of the Western Rub' al-Khali graben system may also be regarded as a potential source rock. The faulting associated with the graben system is terminated by a major unconformity which separates the syn-rift sequence from the post-rift sandstones of the Saq Formation of Saudi Arabia.