The carbonate sediments and paleoenvironmental consideration from the Baba Formation (Oligocene) Kirkuk area, Zagros basin, Northeastern Iraq

This study investigates the carbonate sediments and paleoenvironment of the Baba Formation using samples from the Bai Hassan Oil Well-4 and Kirkuk Oil Well-19 in the Zagros Basin, northeastern Iraq.A total of fifty samples were collected from Bai Hassan Oil Well-4 and twenty from Kirkuk Oil Well-19.The larger foraminiferal assemblages within the Baba Formation at these sections were classified into seven main genera: Lepidocyclina, Miogypsina, Miogypsinoides, Amphistegina, Austrotrillina, Pararotalia, and Nummulitidae, along with Alveolinids, coralline algae, and encrusting foraminifera.A quantitative analysis of thin sections revealed variations in the abundance and distribution of these taxa across different stratigraphic units.In Kirkuk Well-19 Lepidocyclina and encrusting foraminifera were notably abundant in the lower units, while Nummulitidae was more prevalent in the upper units.In contrast, Bai Hassan Well-4 showed a more uniform distribution of Lepidocyclina and Amphistegina, with localized peaks in encrusting foraminifera abundance in the upper unit.The findings indicate that carbonate sedimentation in the Baba Formation consists of four distinct microfacies: 1) Fine to very coarse bioclastic larger foraminiferal packstone grading to grainstone; 2) Fine to very coarse bioclastic larger foraminiferal packstone; 3)Fine bioclastic smaller foraminiferal packstone;4) Fine bioclastic smaller foraminiferal wackestone transitioning to dolostone.The depositional environment of the Baba Formation is interpreted as an isolated slope or platform setting, with open marine conditions prevailing throughout the period of deposition.