Facies analysis and depositional environment of Gir Bir Formation, Northwestern Iraq

Volume 1 , Issue 1 , January 2016 , Pages 373-389

Authors

¹ Geology Department, Mosul University, Iraq

² North Oil Company, Kirkuk, Iraq

Upper Cretaceous successions of the Gir Bir Formation (Cenomanian-Early Turonian)

were studied in 15 wells from northwestern Iraq. The formation is composed of

recrystallized, partly dolomitized limestone with local silicification. Benthonic

foraminifera (Miliolids, Alveolina, and Orbitolina), rudist and peloids are the main

constituents. The studied succession has been affected by several diagenetic events such

as; dolomitization, recrystallization, micritization, dissolution, compaction and

silicification. Facies analysis revealed that seven microfacies subdivided into eleven

submicrofacies could be distinguished, reflecting sedimentary environments including;

deep shelf margin, slope/shoal, rudist buildups, back reef/shoal, and protected lagoon in

a regressive shallowing-upward sequence. Lateral facies variation showed that reefal

facies were commonly located in northwestern parts of the study area, whereas lagoonal

facies existed in eastern and southeastern parts. Rimmed carbonate platform is the

acceptable model for the Gir Bir Formation.

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