Calcareous nannofossils of the late Eocene to early Oligocene from the Pabdeh and Asmari transition in Dezful Embayment (southwestern Iran): Evidence of a climate cooling event

Abstract

Calcareous nannofossil assemblages have been investigated in the uppermost Eocene to the lowest Oligocene in the Marun oil field in the Dezful Embayment (south‐west Iran). The studied interval includes shales, marlstones and limestones. Seventeen genera and 35 species of calcareous nannofossils have been determined. Regarding the succession of nannofossil bioevents, the studied interval ranges from the late Eocene (Priabonian, CNE18 Zone or NP18 Zone) to the early Oligocene (Rupelian, CNO2 Zone, or NP22 Zone). A high relative abundance of warm water taxa (such as Sphenolithus spp., Discoaster spp. and Helicosphaera spp.) is recorded in the late Eocene, while towards the Eocene–Oligocene boundary (EOB), an increase in the relative abundance of cool and temperate taxa (such as Reticulofenestra spp., Cyclicargolithus floridanus, Dictyococcites bisecta and Markalius inversus) is identified. A marked decrease in the abundance of warm water taxa along with a decrease in species diversity indicates that the cooling event at the EOB in the Marun oil field in Iran is similar to other parts of the world (Tethys realm).