Planktonic foraminiferal biostratigraphy of the Farrokhi Formation and determination of the Campanian/Maastrichtian boundary in Central Iran

Abstract

The Cretaceous Farrokhi Formation is located in the Khur area of central Iran and yielded a reasonably well-preserved rich planktonic foraminiferal assemblage. This formation consists of 154 m of fossiliferous marl and limestone. The lower and upper bounding surfaces of the Farrokhi Formation are unconformable with the underlying Haftoman Formation and the overlying Chupanan Formation. In this research, 46 planktonic foraminiferal species belonging to 19 genera were identified and resulted in recognition of the following three biozones (from base to top); the Globotruncana aegyptiaca Interval Zone (IZ), the Gansserina gansseri IZ, and the Contusotruncana contusa IZ. This biozonal framework places deposition of the Farrokhi Formation during the late Campanian to early Maastrichtian. Biostratigraphic comparison between the samples for this research and data from three other studied sections within the Farrokhi Formation indicates that the basal and upper boundaries of the formation are time-transgressive and migrate chronologically from north to southeast. Since the first occurrences of Pseudoguembelina palpebra and Rugoglobigerina pennyi mark the latest Campanian worldwide, we approximate the Campanian/Maastrichtian boundary based on the FOs of Trinitella scotti and Rugoglobigerina hexacamerata, and identify the basal Maastrichtian by the last occurrence of Laeviella bollii.