Facies characterization and depositional environment of Baluti Formation (Late Triassic) from selected sections in the Kurdistan region, Northern Iraq

Abstract

Facies analysis and depositional environment of Baluti Formation (Late Triassic) were studied from the Galley Derash section in the High Folded Zone and Sararu section in Northern Thrust Zone, from Duhok area, Kurdistan region, Northern Iraq. Lithologically, the Galley Derash section comprises 73 m brecciated dolomitic marly limestone, bedded dolomitic limestone, and brecciated sandy limestone which all interbedded with dark gray shale, while in Sararu section, it comprises 90 m of sandy dolomitic limestone interbedded with gray shale and brecciated marly limestone. Depending on field observations and petrographic analysis, three different litho units were recognized in the Baluti Formation in Galley Derash section and the same numbers of litho units were recognized in Sararu section with slight difference in lithology comparing to the Galley Derash. The petrographic study of the formation is based on 32 thin sections which showed that the majority of carbonates are carbonate mud (micrite) with less sparite. The skeletal grains include benthic foraminifera, dasycladacean algae, calcareous red algae, ostracods, brachiopods, bivalves, calcispheres, echinoderms, gastropods, ammonoids, and bioclasts. Non-skeletal grains involve peloids, extraclasts, intraclasts, and ooids. Based on detailed microfacies analysis of carbonate and field description, nineteen lithofacies types are distinguished in both studied sections of Baluti Formation. These facies were grouped relating to their environmental interpretation, into three basic types of facies associations: back shoal/lagoon, shoal, and foreshoal/slope. The field observation and petrographic, facies, and textural analysis indicate that Baluti Formation was deposited in the lower part of the lagoonal environment which changed into shoal and foreshoal/slope toward the upper part in the Galley Derash section, whereas in Sararu section, it was deposited under back shoal/lagoonal conditions including repeated intervals of shoal environment which changed into foreshoal/slope in the upper part.