Depositional Setting of the Shiranish Formation (Campanian-Maastrichtian) in Selected Sections from Northern Iraq

Abstract

The Shiranish Formation (Campanian-Maastrichtian) was studied in two surface sections (Diana and Garuta) in Erbil Governorate. Both sections lie within the High Folded Zone of Zagros Fold-Thrust Belt in Iraq. Stratigraphically, the formation is divided into three lithostratigraphic units depending on the field characteristics with varied thicknesses of the formation in both sections. The lower unit (Unit A) consists of blue to grey well-bedded marly massive limestone, the middle unit (Unit B) is composed of blue to grey marl, marly limestone and stratified shale, and finally, the upper unit (Unit C) is composed of grey limestone and blue marly limestone. The lower contact of the formation is unconformable with the Bekhme Formation in the Diana section and conformable with the Kometan Formation in the Garuta section, while the upper contact is conformable with both Tanjero and Kolosh formations in Diana and Garuta sections respectively. X-ray diffraction analysis has revealed that calcite is the main mineralogical component with less of quartz and clay minerals as represented by chlorite and illite. Four lithofacies were distinguished (Marl facies (Sml), Shale facies (Ssl), Conglomerate limestone facies (Scl)) and red clay layers (Srl), whereas, three main microfacies were recognized; Fossiliferous Lime Mudstone Microfacies (Sml), Lime Wackestone Microfacies (Sw) and the Packstone Lime Microfacies (Sp), which in turn were subdivided into seven secondary facies, according to their components, which are; Planktonic Foraminiferal Lime Wackestone Submicrofacies (Sw1), Keeled Planktonic Foraminiferal Lime Wackestone Submicrofacies (Sw2), Calcispheres Lime Wackestone Submicrofacies (Sw3), Bioclastic Lime Wackestone Submicrofacies (Sw4), Benthonic Foraminiferal Lime Wackestone Submicrofacies (Sw5), Keeled Planktonic Foraminiferal lime Packstone Submicrofacies (Sp1) and Planktonic Foraminiferal Globular Chamber Packstone Submicrofacies (Sp2 ). Based on these facies, the formation was deposited in a relatively deep marine environment and within two secondary environments; the outer shelf and upper bathyal environments as a result of the widespread transgression in the beginning of the Campanian.