Biostratigraphy and depositional setting of the carbonate unit within the upper part of the Maastrichtian Tanjero Formation in the Khanaqa Village, Imbrication Zone, NE Iraq-Kurdistan region

This study investigates the biostratigraphy and depositional environment of a carbonate unit located in the upper part of the Tanjero Formation, exposed in Khanaqa Village within the Imbrication Zone of northeastern Iraq. The unit comprises approximately three meters of massive and thick-bedded, sandy, yellowish-grey, fossiliferous limestone, with thin intercalations of marly bioclastic limestone in its lower section. Petrographic analysis, based on 18 thin sections, reveals a diverse assemblage of shallow-marine macrofossils and microfossils, including corals, rudists, various benthic foraminifera, and algae. Microfacies analysis identified three dominant microfacies, further subdivided into eight types, all characteristic of reefal environments. The benthic foraminiferal assemblages indicate a Maastrichtian age for the studied deposits. Based on lithological, petrographic, and paleontological evidence, the overall characteristics of the carbonate unit are more consistent with those of the Maastrichtian Aqra Formation. The occurrence of the Aqra Formation within the upper part of the Tanjero Formation in the studied area reflects a significant sea-level change, concurrent with tectonic activity in the Tanjero Basin during the latest Cretaceous period in the Kurdistan Region of northern Iraq.