Micropalaeontology of the Saudi Arabian Rus, Dammam and Dam Formations Exposed at the Dammam Dome

Geraint W. Hughes* and Saleh Enaizy
Saudi Aramco
*[email protected]

The Dammam Dome represents a unique feature in Saudi Arabia as it forms a local topographic high along the otherwise flat extent of the eastern flank of the Kingdom. Its origin is attributed to episodic upwards movement of a deep-seated infra-Cambrian evaporite plug. The Rus, Dammam and Dam formations are exposed, of which their diminished thickness, relative to the adjacent subsurface, testifies to the region being regionally positive during the Tertiary. Micropalaeontological analysis with revised taxonomy of old and new exposures has improved palaeoenvironmental interpretation. The Paleocene to Early Eocene Umm er Radhuma is the lowermost Tertiary formation, but is not exposed in any accessible locations and will not be considered here. The Rus Formation was defined on the Dammam Dome, and includes lower carbonate and upper carbonate-evaporite unit. A new exposure on the Dammam Dome provides evidence for a lowermost Rus unit consisting of interbedded transgressive marls and clean highstand carbonates. An Early Eocene age is assigned on stratigraphic position as microfossils are rare owing to predominantly shallow-marine, periodically hypersaline conditions. The Dammam Formation includes the Midra, Saila, Alveolina and Khobar members. The Alveolina and Khobar members contain rich and diverse benthonic foraminiferal biofacies, including Middle Eocene Alveolina, Nummulites and Discocyclina species. A new Dhahran Member is proposed for the transgressive marls between the Alveolina and Khobar highstand carbonates. The pre-Neogene angular unconformity underlies the Middle Miocene Dam Formation. The Dam Formation includes a basal stromatolite unit that is overlain by a coral and rich benthonic foraminiferal succession that contains Borelis melo.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain