Thick sedimentary sequences from the Phanerozoic [citation needed](including sandstone, anhydrite, dolomite, limestone, chert and marl) dominate much of the country's surface and host oil.
Within these younger rocks, a large western facing escarpment formed in central Saudi Arabia, capped with limestone.
Basement rock dips away from the escarpment with thicker sediments in the Rub' al Khali and the Persian Gulf region.
Jurassic rocks form much of the escarpment in central Saudi Arabia, although discontinuous sedimentation led to the deposition of calcarenite and anhydrite.
[9] The early and middle Eocene Damman Formation is named for the Dammam Dome and includes basal marl, limestone and dolomite as well as the Saila Shale Member.
The marl, limestone and shale units taken together do store groundwater and communities in the Eastern Province often draw on the Alat aquifer in the Khobar Member.
At the northwest edge of Harrat Hutaym are marl, sandstone and basal conglomerate deposits with ostracode fossils from a freshwater environment, inferred to be from the Pliocene.
Its olivine basalt and aplite dikes formed during the Miocene, Pliocene and early Quaternary, spanning 250 kilometers to the northwest from Ath Thayat into Jordan.
[10] In the last 2.5 million years of the Quaternary, limestone-quartz terrace gravel deposited in Wadi al Batin, occurring 60 to 90 kilometers north of the Trans-Arabian Pipeline.
Sheet gravel blankets the Ad Dibdibah Plain, with quartz, carbonate and metamorphic rock grains spanning into Iraq and Kuwait.
An Nafud and Ar Rub al Khali have silt, gravel, sabkha, unconsolidated sands and coral limestone from the geologically recent past.