Microfacies and reservoir quality of the Middle Cretaceous Rumaila Formation in the AD oilfield, central Mesopotamian Basin, southern Iraq

•Ten carbonate microfacies deposited in five sedimentary facies belts are identified in the Rumaila Formation.•Rapid sedimentary facies changes were organized into three RST and two TST caused by frequent relative sea-level changes.•Reservoir quality is related with carbonate microfacies types.•Differential early diagenesis causes distinct contrasts of pore evolution for the same primary rock texture.•Reservoir quality of the Rumaila is jointly controlled by sedimentary facies variation and differential early diagenesis.