The modified lithostratigraphic framework of the Kirkuk (northern Iraq) carbonates shows that the Paleocene shoal/shelf facies graded northward into the nearshore dolostones and southward into the offshore (basinal) limestones. During Eocene time the shoal deposition covered the whole shelf area, with basinal equivalents present in the southwest. In contrast, the two major cycles of Oligocene sedimentation were controlled by shelf-edge bioherms (in-situ mechanical pilings of skeletal grains). In the Baba-Tarjil area, the bioherms grade laterally into mud flat (NW to NE) and basinal (SE to SW) facies.

Subaerial exposure caused cementation, dolomitization, and dissolution; moldic porosity being the dominant factor controlling the porosity development in the Kirkuk oil reservoir. The associated fine-grained dolostones of the Paleocene time show petrographic, chemical, and isotopic characteristics of the hypersaline (sabkha) type, whereas their coarse-grained Eocene and Oligocene counterparts resemble the diagenetic (Dorag) type dolostones.

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