Lithofacies and Microfacies Study of ATE Maastrichtian Reefal Limestones and Comparison with the Aqra Formation, Northeast and Northern Kurdistan Region-Iraq

Abstract

The Maastrichtian reefal limestone, which developed variably across the northern and northeastern Kurdistan Region of Iraq, includes the Aqra Formation, which formed extensive platforms in the Aqra-Barzan area throughout the Maastrichtian period. Additionally, bars and lenses of reefal limestone in the upper part of the Tanjero Formation created longitudinal submarine ridges in the Arabian-Eurasian Foreland basin. This study selected three sections: the Aqra Formation in the type section and study the reefal limestone lenses in the Upper part of the Tanjero Formation at the Kunamasi and limestone bars in the Balakaity. Focusing on lithofacies and microfacies to determine if these reefal limestones are part of the Aqra Formation. The type section of the Aqra Formation, located in the Aqra area, features significant reefal limestone approximately 700 meters thick, including rudists with bitumen and some dolomite content. This formation is widely deposited in the Aqra and Barzan areas, overlying the Bekhme platform stratigraphically, and extends geographically from Bujel to Chia Gara anticlines. Four submicrofacies identified in this reefal limestone are Miliolids packstone, Rudists floatstone, Peloidal grainstone, and Bioclastic foraminifera grainstone. In the Kunamasi area, the reefal limestone appears as thick deposits associated with marl and sandy claystone beds, approximately 30 meters thick, and situated above the flysch Tanjero Formation. Key submicrofacies here include Omphalocyclus packstone, Rudists floatstone, and Echinoids grainstone. At the Balakaity section, the reefal limestone consists of a single, thick body exceeding 50 meters in thickness, directly overlying the Tanjero Formation and restricted to the Dar-Alsalam area. The submicrofacies in this section include Foraminifera packstone, Omphalocyclus packstone, and Rudists floatstone. Overall, the microfacies interpretation is the Aqra Formation is deposited as a large platform in inner and middle ramp settings. Conversely, the reefal limestone in the Balakaity and Kunamasi areas appears to be part of submerging islands within the flysch marine environment of the Tanjero Formation during the active Arabia-Eurasian Subduction. Based on depositional context and microfacies analysis can be concluded the reefal limestone in these areas is more likely associated with the Tanjero Formation rather than the Aqra Formation.