oa Basin evolution of the Paleozoic successions of Iraq

The study addresses the basin evolution of the Paleozoic sequences in Iraq. It integrates petrographical and lithological data from deep exploration wells and outcrops in northern Iraq to better understand the sedimentary environments and to evaluate the depositional and tectonosedimentary evolution of the basin. The Paleozoic successions are represented by five intra-cratonic sedimentary sequences. These are dominated mainly by siliciclastic and mixed sedimentary packages, and are separated by<br>major and minor unconformities. These cycles are: (1) Ordovician cycle, represented by the Khabour Formation; (2) Silurian cycle, represented by the Akkas Formation; (3) Mid- and Late Devonian to Early Carboniferous cycle, represented by the Chalki, Pirispiki, Kaista, Ora and Harur formations; (4) Permian-Carboniferous cycle, represented by the Ga’ara Formation; and (5) Late Permian cycle, represented by the Chia Zairi Formation. The Ordovician Khabour Formation appears to have been deposited in a shallow-marine environment during several transgressive and regressive cycles. The Silurian Akkas shale was deposited in an open-marine environment. The Late Devonian to Early Carboniferous depositional regimes are considered to be continuous and set<br>in a vast subsiding basin that reflected epicontinental or epeiric seas in a homoclinal ramp setting. The Permian-Carboniferous Ga’ara Formation was deposited in a deltaic to fluvial environment, while the Late Permian Chia Zairi Formation represents carbonate platform deposition. The potential source rocks may include some shale beds of the Khabour Formation, the hot shales of Akkas Formation and the shales of the Ora Formation. The sandstones of the Khabour, Akkas and Kaista formations have good reservoir potential. The Late Permian carbonates of Chia Zairi Formation may be self-sourcing and contain multiple reservoirs. Basin analysis demonstrates the evolution and architecture of the basin and gives an insight into the effects of the Caledonian and Hercynian<br>epeirogenic movements on the tectonostratigraphy history of the region.