An analysis of three selected wells in the Ain Zala oil field (AZ-16, AZ-17, and AZ-24) in the northwestern part of Mosul Governorate. In terms of biostratigraphy, it consists of planktonic and suspended foraminifera, which comprise 37 species belonging to 17 genera. Based on the recorded planktonic foraminifera, three main biozones were identified: Globotruncana aegyptiaca Partial Zone, which refers to the age of the Late Campanian, Gansserina gansseri Partial Range Zone, which indicates the age of the Early Maastrichtian, and Abathomphalus mayaroensis Interval Zone, which indicates the age of the Late Maastrichtian. The Abathomphalus mayaroensis Interval Zone is divided into four subzones: Racemiguembelina fructicosa Partial Range Subzone, which indicates the age of Early Late Maastrichtian, Pseudoguembelina hariaensis Partial Range Subzone, which refers to the age of Middle Late Maastrichtian, Pseudoguembelina palpebra Subzone, which covers the age of Late Late Maastrichtian, and Plummerita hantkeninoides Subzone, which refers to the age of Latest Maastrichtian. The Shiranish Formation in northwestern Iraq was deposited during the Cretaceous period, from the Late Campanian to Late Maastrichtian. The stratigraphy of this formation consists mainly of marl and marly limestone.
