Surface Geology of Dammam Dome, Eastern Province, Saudi Arabia

Abstract

The Dammam dome, located in the Eastern province of Saudi Arabia, is an oval-shaped structure with a 9-mi-long major axis trending N30-40°W and covering an area of about 60 sq mi. Superimposed on the dome are several folds and slump blocks. Slumping is believed to be primarily the result of undercutting of softer sediments. No faults were noted at the surface, but faulting at depth is not precluded. Sediments ranging in age from early Eocene to middle Miocene are exposed at the surface of the dome. They consist of a thin sequence of Umm Er Radhuma Formation dolomites at the base, overlain by a full section of Rus Formation composed of dolomites; dolomitic limestones with quartz, calcite geodes, and marls; and toward the top of the formation, soft, white, chalky beds with minor calcarenitic limestone and gypsiferous shale. The Dammam Formation overlies the Rus and is widely exposed along the rimrock encircling the dome, with scattered exposures within the dome itself. The Dammam Formation consists of the Midra and Saila Shale Members at its base, followed by the Alveolina Limestone Member, and the Khobar Member marl and nummulitic limestone. Miocene Dam sediments unconformably ove lie the Eocene. They consist of an algal-coralline-molluscan reef complex at Jabal Umm Er Rus, the highest topographic point on the dome, and they grade into molluscan-rich calcarenites and calcirudites with subordinate stromatolites and argillaceous limestone on the western flank, as at Jabals Midra al-Janubi and Shamali. The uppermost Dam beds exposed at these two localities on the summit cliffs consist of microcrystalline dense limestone.