Coniacian/Santonian calcareous nannofossil and planktonic foraminifera in the Kurdistan Region, NE Iraq: biostratigraphy and bioevents

Abstract

Calcareous nannofossil and planktonic foraminiferal biostratigraphy and bioevents in the Zewe section situated in the Kurdistan Region, NE Iraq, have been described in detail. High-resolution standardization of Coniacian/Santonian calcareous nannofossil and planktonic foraminiferal biostratigraphic datums categorized the reviewed succession into two nannofossil (CC15 and CC16) zones which are utterly equivalent to two planktonic foraminiferal (Dicarinella concavata and D. asymetrica) zones. The Coniacian/Santonian stage boundary was fixed based on the FOs of the premium reliable calcareous nannofossil and planktonic foraminiferal assemblages. The successive bioevents, in stratigraphic order, characterizing the Coniacian/Santonian stage boundary in the conspicuous inspected section are as follows: the FOs of Lithastrinus grillii (Upper Coniacian); Lucianorhabdus cayeuxii (Uppermost Coniacian); and Micula concava (Lowermost Santonian). Other nannofossil assemblages in Zone CC16 are the FOs of Radiolithus planus, Quadrum giganteum, and Eprolithus floralis. The planktonic foraminiferal bioevents are as follows: the FO of Dicarinella asymetrica (Upper Coniacian), followed upward by the FO of very rare Sigali carpatica (Uppermost Coniacian) and common Globotruncana linneiana at the base of the Santonian stage.