MICROFACIES AND DEPOSITIONAL ENVIRONMENT OF CHIA GARA FORMATION (UPPER JURASSIC – LOWER CRETACEOUS) IN KURDISTAN REGION, NORTHERN IRAQ

Abstract

The depositional environment of Chia Gara Formation (Upper Jurassic – Lower Cretaceous) in Northern Iraq is studied. The formation is exposed in the High Folded Zone, and Imbricated Zone of Iraq. The selected sections for this study are Banik (outcrop), Barsarin, (outcrop) and well Aj-12; located in the High Folded, Imbricated, and Foothill Zones respectively. The Chia Gara Formation is lithologically composed of black shale, thinly bedded brown argillaceous limestone, thin to medium limestone, and marly limestone in uppermost part. Skeletal grains consist of macro and micro pelagic fauna. Pelagic fossils include Ammonites, radiolarian (Spumellarian Group), ostracods, planktonic forams (Globigerina), pelecypods, and others. Non-skeletal grains are not observed in the current study. The groundmass of the Chia Gara Formation is dominated by micrite which is often replaced by coarser microspar. Limestones of Chia Gara Formation are divided into three principal microfacies: Mudstone, Wackestone, and Packstone. Each of these is further subdivided into submicrofacies. Using lithology, paleontology, and microfacies criteria, the most likely depositional environment of the Chia Gara Formation is concluded as toe of slope to deep open marine environment.