Upper Albian-Turonian foraminifers and radiolarians from the Kelevudag section, northeastern Azerbaijan

Abstract

New data on planktonic and benthic foraminifers and radiolarians derived from the upper Albian-Turonian sediments of the Kelevudag section, northeastern Azerbaijan, are reported. Two planktonic foraminiferal biostratigraphic units are recognized, namely, the Thalmanninella deeckei Beds (uppermost lower–lowermost middle Cenomanian, top of the lower part of the Kemishdag Formation) and Dicarinella hagni Beds (lower Turonian, top of the upper part of the Kemishdag Formation). Two units, the Pseudovalvulineria cenomanica–Berthelina berthelini Beds (middle–upper Cenomanian, top of the lower part of the Kemishdag Formation) and Lingulogavelinella globosa Beds (upper Cenomanian–lower Turonian, top of the upper part of the Kemishdag Formation), are distinguished by benthic foraminifers. On the basis of the radiolarian studies, the following units are defined: the Dorypyle — anisa–Pseudodictyomitra languida Beds (upper Albian, upper part of the Kyulyuli Formation), Patellula spica–Crolanium triangulare Beds (lower Cenomanian, base of the lower part of the Kemishdag Formation), Pseudoaulophacus lenticulatus–Thanarla gracilis Beds (middle Cenomanian, top of the lower part of the Kemishdag Formation), and the Orbiculiforma quadrata–Pseudodictyomitra pseudomacrocephala Beds (uppermost upper Turonian, lower part of the Kemchi Formation). The age estimates available from foraminifers and radiolarians do not contradict each other. The time of accumulation of the Kemishdag Formation was previously considered within only the Cenomanian. According to the new available foraminiferal data, the range of the Kemishdag Formation is widened and it is believed to correspond to the Cenomanian–lower Turonian. On the basis of foraminiferal and radiolarian studies, the stratigraphic position of the lower boundary of the Kemchi Formation is determined within the Turonian and the Turonian–Coniacian boundary is defined in the lower part of the Kemchi Formation.