Biofacies and Sedimentology of the Dammam Dome, Saudi Arabia
Hughes, Geraint W.*1; Lindsay, Robert F.1; Cantrell, David L.2; Naji, Nassir S.1
(1) Exploration Technical Services, Saudi Aramco, Dhahran, Saudi Arabia. (2) Exploration Advanced Research Centre, Saudi Aramco, Dhahran, Saudi Arabia.
The Dammam Dome forms a significant topographic high on the east flank of the Arabian Peninsula, and consists of exposures of Tertiary sediments. This feature led to oil discovery in Saudi Arabia within the Upper Jurassic Arab Formation, and is attributed to episodic uplift by infra-Cambrian salt, comparable with the Awali Dome of Bahrain. While the Paleocene Umm Er Radhuma Formation is not exposed, the overlying succession is well exposed commencing with the Lower Eocene Rus Formation followed by the Middle Eocene Dammam Formation and then by the Middle Miocene Dam Formation. Despite representing a much thinner succession than is present off-structure, new measured sections reveal additional aspects of depositional cyclicity that, with biofacies, add new insights to the sedimentological and palaeoenvironmental history of the region.
The Lower Eocene Rus Formation consists of interbedded dolomites, soft mudstones and remnants of evaporites with sparse biofacies indicative of hypersaline, shallow marine conditions. A short-lived unconformity separates the Rus from the overlying Dammam Formation, in which the mudstones of the Midra and Saila members and carbonates of the Alveolina and Khobar members are well developed. Age-indicative biofacies combined with lithofacies trace the rapid flooding of the platform and development of fine-scale palaeoenvironmental variations within an extensive shallow marine lagoon. A major unconformity, known as the Pre-Neogene Unconformity, separates the Palaeogene formations from the overlying Middle Miocene Dam Formation. The basal Dam transgression is well exposed and contains reworked clasts of the Rus and extensive stromatolites with some reworked stromatolites indicating a slow but high energy transgression. Later deeper conditions and lagoon development are suggested by the overlying normal marine microbiofacies that contain diverse foraminifera and corals. The Lower Miocene Hadrukh Formation is not present on the Dome and its absence is attributed to non-deposition as it is present in the offshore subsurface. The Hadrukh contains a unique biofacies that includes charophyte oogonia and crustacean fragments indicative of a very shallow marine depositional environment.
These Tertiary formations are of interest as they host the Hasbah, Hadrukh and Dam reservoirs in offshore fields of Saudi Arabia.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain