Sedimentology of Late Jurassic–Early Cretaceous Chia Gara Formation in Rawanduz area, Kurdistan region-Iraq

Detailed sedimentology of the Chia Gara Formation has been studied in the Faqiyan section, High Folded Zone, Kurdistan region of Iraq. The studied outcrop was explored for the first time by analyzing thin sections, X-ray diffraction (XRD), and scanning electron microscopy (SEM) to clarify the depositional environment of the formation. The formation comprises 80 m of limestone interbedded with thin-bedded dark brown shale and argillaceous limestone. It overlies the Barsarin Formation and underlies the Sarmord Formation with conformable and gradational contacts. Based on the petrographic investigation, the main skeletal components of the carbonate rocks of the formation are radiolarian, foraminifera, calcispheres, ammonites, and pelagic pelecypods. The main diagenetic features that affected the carbonate rocks of the Chia Gara Formation include micritization, neomorphism, early dolomitization, cementation and dissolution. The XRD and SEM analyses of selected shale samples show that the main non-clay minerals are calcite and quartz, while the clay mineral is kaolinite. Three main types of microfacies were identified in the carbonate of the Chia Gara Formation and divided into six submicrofacies to determine and interpret the depositional setting of the formation in the Faqiyan section. Petrographic analysis, field observation and microfacies analysis indicate that the Chia Gara Formation in the Faqiyan section was deposited in basinal deep water and a deep shelf environment.