Evidence of early Aptian Oceanic Anoxic Event 1a (OAE1a) in the Central Kopet-Dagh (Qaleh-Zoo section), with special reference to the calcareous nannofossil assemblages

In the current study, a succession from the middle part of the Sarcheshmeh Formation was investigated to record the early Aptian oceanic anoxic event 1a (OAE1a) at the Qaleh-Zoo section in the central part of the Kopet-dagh Basin. The OAE1a has been recorded on a global scale during the early Aptian in the NC6B nannofossil biozone. In this study the interval from the uppermost part of NC6A to the lowermost part of NC7A (early Aptian) was investigated at Sarcheshmeh Formation. Calcareous nannofossil paleoecology and carbonate calcium contents were analyzed to identify the OAE1a interval. Rare presence or absence of nannoconids at NC6B along with the lowest values of carbonate calcium contents indicate the effect of OAE1a in the study section (55 to 180 meters of the studied interval). Regarding these data (calcareous nannofossils and carbonate calcium contents), the OAE1a was recorded at the middle part of Sarcheshmeh Formation which is equivalent with this event at the western part of the Kopet Dagh Basin (Takal Kuh section).