Microfacies Analysis and Depositional Environment of the Late Cretaceous Shiranish Formation in the Selected Section, Safin Anticline, Northern Iraq

Abstract

This study concerns microfacies and environmental environment of the Late Cretaceous Shiranish Formation in the Sulawki Saru section, Safin anticline, northern Kurdistan region, Iraq. Shiranish is lithologically composed of 81 m of thin to medium and fractured bedded grey to white limestone in the lower part and grey to blue bedded marly limestone characterised by joints in the upper part. Its lower boundary is conformable with massive dolomitic limestone of the Bekhme Formation, while upper boundary is not clear and covered by sedimentary material. The petrographic investigations of limestone with a microfacies analysis of carbonate rocks were based on (31) thin sections. The petrographic study revealed that the majority of matrix are micrite with occasional recrystallized microspar. The skeletal grains exhibit a diverse range of pelagic marine fauna, including planktonic foraminifera (Rugoglobigerina, Heterohelix, Globotruncana, Globotruncanita, Hedbergella, and Oligostegina), benthonic foraminifera (Lenticulina, Rotalia, and Bolivionoides), calcispheres, ostracods, echinoids, and bioclasts. Based on field investigations and petrographic examinations, two different lithological units were identified in the Shiranish Formation at the Sulawki Saru Section. They are arranged from older to younger: a-Fractured bedded limestone unit. b-Bedded marly limestone unit. Based on systematic microfacies study of limestones, two major microfacies and 9 submicrofacies are distinguished in the studied locality of the Shiranish Formation. Integrating all petrographic, facies, and textural evidences, it is concluded that the depositional environment of Shiranish Formation in the Sulawki Saru section was basinal environment (deep shelf) in lower part changed to outer shelf in the upper part with quiet, semi-reducing conditions.