Abstract The Campanian-Maastrichtian Abtalkh Formation of the Kopet-Dagh Basin (NE Iran) has been studied for biostratigraphic purposes. The present study integrates results from three sections within the basin: Maraveh-Tapeh (Western Kopet-Dagh), Abtalkh Village and Qareh Sou (Eastern Kopet-Dagh). The biostratigraphic distribution of 59 species of planktonic foraminifera has been used to characterize the following zones: Globotruncanita elevata PRZ, Contusotruncana plummerae IZ, Globotruncana falsostuarti IZ, Radotruncana calcarata TRZ, Globotruncanella havanensis IZ, Globotruncana aegyptiaca IZ, Gansserina gansseri IZ, Contusotruncana contusa IZ, Abathomphalus mayaroensis IZ. The last three zones were identified within the Maraveh-Tapeh basin only. In addition, the secondary biozonation was determined based on the distribution of Heterohelicidae within the Maraveh-Tapeh section and includes: Laeviheterohelix dentata IZ, Pseudotextularia elegans IZ, Pseudotextularia excolata IZ, Planoglobulina acervulinoides IZ, Racemiguembelina fructicosa IZ. The Abtalkh Formation is shown to be limited to the Campanian and represents an earliest-late Campanian age in the eastern part of Kopet-Dagh Basin (Qareh Sou, Abtalkh Village). At Maraveh-Tapeh (Western Kopet-Dagh) it is dated as middle Campanian-late Maastrichtian.

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