Paleoenvironments and Sequence Development of the Miocene succession , Western and Southern Iraq


The Miocene succession of western and southern Iraq is represented by the Euphrates, Ghar, Jeribe, Nfayil, Fatha, and Injana formations. The Euphrates Formation (Early Miocene) consists mainly of shallow marine facies; it`s equivalent the Ghar Formation (Early- Early Middle Miocene) is represented by continental clastic facies. The Jeribe Formation (Early Middle Miocene) represents shallow marine environment. The Nfayil Formation (Middle Miocene) also of shallow marine environment, it`s equivalent the Fatha Formation is represented mainly by supratidal marine environment. The Injana Formation (Late Miocene) represents the clastic continental facies. The studied succession was highly affected by many diagenetic processes such as dolomitization, dedolomitization, dissolution and cementation with less effective micritization, neomorphism, and compaction. Four third order cycles were recognized in the studied sections, These include: cycle A of the Miocene Euphrates Formation and it`s equivalent the lower part of the Ghar Formation, cycle B of the Early Middle Miocene Jeribe Formation and it's equivalent the upper part of the Ghar Formation, cycle C of the Middle Miocene Nfayil Formation and it`s equivalent the Fatha Formation, and cycle D of the Late Miocene Injana Formation. Each third order cycle can be subdivided into a number of fourth order cycles. All of the fourth order cycles are assymmetrical reflecting an imbalance between the relative sea level and carbonate production. A variation between the different sections in nature of cyclic deposition reflects the difference of local tectonic effect on the sequence development.