A biostratigraphic study based on the planktonic foraminifera and isotope stratigraphy of the Cenomanian-Turonian interval has been undertaken in the western part of the Kopet-Dagh Basin (NE Iran). In this research,two stratigraphic sections including Maraveh Tappeh and Qareh Galdy have been sampled and studied. Basedon planktonic foraminifera, three biozones were assigned to this interval. These are the Rotalipora cushmaniZone, Whiteinella archaeocretacea Zone and Helvetoglobotruncana helvetica Zone. These biostratigraphic dataconfirm a gradual faunal turnover of planktonic foraminifera, at the Cenomanian-Turonian boundary inWhiteinella archaeocretacea Zone characterized by: absences, low abundance and disappearances of complexmorphotypes. After this event, in Helvetoglobotruncana helvetica Zone, along with simple globular chambermorphotypes, single keeled and double-keeled morphotypes appeared and flourished.The carbon-isotope curves in both sections, record a negative shift values below the Aitamir-Abderaz formationsboundary in Whiteinella archaeocretacea Zone, and then, a positive excursion of about 5.50‰, along withseveral fluctuations are well evident in both sections. The δ18O values show, from the bottom to the top, agradual increase of averagely 2‰. Based on these results, the Cenomanian-Turonian succession in this part ofthe Kopet-Dagh Basin is continuous and corresponds to the siltstone and chalky limestone layers of the upperpart of the Aitamir Formation and the lower part of the Abderaz Formation.
|Numero di pagine||14|
|Rivista||Journal of African Earth Sciences|
|Stato di pubblicazione||Published - 2018|
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