Facies development and paleoenvironment of the Hajajah Limestone Member, Aruma Formation, central Saudi Arabia

• The Campanian Hajajah Member of the Aruma Formation was formed during two regressive episodes.
• Each of them formed of intra-shelf basin facies, fore-reef facies and back reef and near-shore facies.
• Hajajah Member deposited in distal marine settings changed upward to fore-reef framework and terminated with shallow facies.

The Campanian Hajajah Limestone Member of the Aruma Formation was formed during two regressive episodes. Each of them formed of three depositional facies, from base to top: 1) intra-shelf basin facies, made up of fossiliferous green shale and mudstone with ostracods and badly preserved foraminifers. 2) fore-reef facies, consists of hard, massive, marly coralline limestone. The upper part is rich with low divers, badly to moderate preserved, solitary and colonial corals, and, 3) back reef and near-shore facies, consists of fossiliferous sandy dolomitized, bioturbated limestone with abundant reworked corals, bivalves, gastropods, and aggregate grains. On the basis of field observations, micro-and macrofossils and microfacies analysis, the Hajajah Limestone Member was deposited in distal marine settings below storm wave base in a low-energy environment changed upward to fore-reef framework in an open marine environment with moderate to high energy conditions and terminated with shallow marine facies with accumulation of skeletal grains by storms during regression.