Depositional Environment and Tectonic Phenomena in the Kometan Formation, Northeastern Iraq

Kometan Formation is studied in a surface section in Dokan region, northeastern Iraq. It attains 70 m thick and its rocks are characterized by the predominance of gray-white limestone and stylolites in most of the section with the presence of chert nodules within the layers of the formation succession, and thin layer of marl in the lower part of the formation. Microfacies study of the rocks reveals that they are mostly composed of two main microfacies: lime wackestone microfacies and lime packstone microfacies which are subdivided into nine submicrofacies according to their grains component. The different microfacies consist of a variety of skeletal grains, such as planktonic and benthic Foraminifera, Calcispheres and Radiolaria. Bioclastes are represented by Foraminifera bioclast and Pelecypoda shells. In addition, the rock succession affected by many diagenetic processes such as compaction, cementation, recrystallization, silicification, dolomitization and dissolution, authigenic minerals such as pyrite and glauconite. Sedimentolgical and biological evidences indicate that the formation was deposited within a deep environment extending from the deep sea to the toe of the slope, which corresponds to all bathyal zones. The study identifies the presence of tectonic features like Neptunian Dykes and Stylolite structures, which are probably formed by tectonic tension processes. Nannofossils suggests that sediment filled Neptunian dykes are relatively younger in age than Kometan Formation.