Calcareous nannofossil biostratigraphy of the upper Cretaceous to lower Paleocene in Zagros Basin, western Iran

Calcareous nannofossil biostratigraphy has been investigated for Upper Cretaceous and lowermost Paleocene deposits in the Garab section located on the northeastern limb of the Kabir Kuh Anticline, Zagros Basin (Iran). The results reveal a relatively complete record that spans the Cenomanian to Danian stages. The base of the section contains Eiffellithus turriseiffelii, implying placement in or above the UC0 Biozone, and the occurrence of Corollithion kennedyi at 68.8 m confirms placement in the Cenomanian. An unconformity is suggested by the missing UC15a-b Biozone in the upper Campanian Gurpi Formation. The Cenomanian/Turonian Boundary (CTB) and Oceanic Anoxic Event 2 (OAE2) is characterized by abundant small taxa including Biscutum constans, Discorhabdus ignotus, and Zeugrhabdotus noeliae, among which the last two taxa are indicators of surface-water fertility during OAE2. The Cretaceous/Paleogene Boundary (KPB) is marked by an increase of abundance of calcareous nannofossils such as Braarudosphaera bigelowii and Neobiscutum spp. and a rapid increase of calcareous dinoflagellates. Our results document high nannofossil productivity during the OAE2, as observed in other Tethyan locations, and rapid turnover and proliferation of disaster taxa such as Braarudosphaera bigelowii, and Neobiscutum spp. at the KPB. These results significantly enhance our understanding of these geological events and suggest that the Garab section is a strong candidate for further study of both the Cenomanian/Turonian boundary and K/Pg boundary.