Facies Analysis And Depositional Environment Of Lower Jurassic (Sehkaniyan Formation), Northeastern Iraq-Kurdistan Region

Abstract

This study deals with the sedimentology and stratigraphy of Lower Jurassic Sehkaniyan Formation as an implication for its facies analysis and depositional environment in Warte area in the Imbrication Zone, NE Iraqi Kurdistan region. In the study area the formation has a thick succession of shallow water carbonates and thin shale represents a real lower Jurassic unit that overlying the Sarki Formation and underlying the Sargelu Formation. The total of 30 thin sections from the carbonates of Sehkaniyan Formation were petrographyicaly studied under polarizing microscope in-order to finding out their petrographic constituents. The petrographic study demonstrated that most of the carbonate units of Sehkaniyan formation subjected to sever dolomitization, although considerable shallow water skeletal garins (bethic foraminiferas, gastropods, pelecepods, ostracods) and non-skeletal grains (Peloids and ooids) in addition to abundant stromatolites are recognized.  Depending on field and petrographic study, the Sehkaniyan Formation subdivided into three units; the lower unit consists of dark grey thick bedded dolomitic limestone and brown to dark brown brecciated dolomitic limestone. The unit comprised of grey to yellowish grey medium to thick bedded limestone and dark grey dolomitic limestone intercalated with thin bedded shale. While, the upper unit consists of dark grey thick bedded dolostone, light grey thick bedded brecciated dolomitic limestone and massive dark grey dolomitic limestone. Three difrint microfacies were recognized that demonstrated a wide range of facies associations, which suggested the deposition of Sehkaniyan Formation in a Shoal, Lagoon and Tidal flat environments in an inner homoclinal ramp setting.