Facies and stratigraphic associations of Sinjar and Khurmala Formation, Dohuk Area, Kurdistan Region, Iraq

Abstract

The carbonate facies of the Lower Eocene Sinjar and Khurmala Formations are stratigraphically interrelated and forms part of the shoaling stage sediments of the Zagros Foreland Basin. This work aims at investigating their stratigraphic associations at Dohuk area of NE Iraq. Both Formations are well exposed in three sections examined from Dohuk area including Spindar (Gara Mt.), Birkyat (Khair Mt.) for Khurmala Formation, and Barbuhar (Bekhair Mt.) for Sinjar Formation. The thickness of the Khurmala Formation varies from 90.7 m at Spindar and 81 m at Birkyat. The thickness of the Sinjar Formation is 36.5 m at Barbuhar section. The focus of this study is to determine the carbonate microfacies in order to construct their sedimentary facies model and to interpret the depositional environment. Lithologically, Khurmala Formation in Spindar and Birkyat sections is closely similar and consisting of buff to gray, medium to thick, well-bedded microbialites dolostone, alternating with thin beds of soft shale and marlstone interlayer. The Barbuhar section consists mainly of three reefal limestone horizons alternating with siliciclastic interlayers. Four intensively dolomitized microfacies were recorded from Khurmala Formaton sections. These are dolo-mudstone, microbial dolo-mudstone, foraminiferal algal dolo-packstone, and foraminiferal dolo-wackestone, whereas Sinjar Formation shows eight carbonate microfacies, which are coraline framestone, bioclastic coralgal rudstone, coralgal foraminiferal bioclastic packstone, foraminifera bioclastic algal packstone, bioclastic forminiferal packstone, dolomitic microbial bindstone, dolomitic microbial laminite, and bioclastic sandy limestone. Field observations, along with microscopic investigations, have resulted in identifying facies types of the two formations. The Khurmala Formation in Spindar and Birkyat seems to be deposited in a shallow shelf setting of supratidal, intertidal, and semi-restricted lagoonal facies with siliciclastic-dominated coastal plain. The section of Barbuhar represents the Sinjar Formation which is deposited at further seaward position of the shelf as a patch reef limestone which is intermixed with the Kolosh Formation sandstone in a further deeper position.