New Data on the Nannofossil and Planktonic Foraminiferal Composition in the Lower Miocene Alkun Formation, Ciscaucasia

Nannofossils and planktonic foraminifers from the Lower Miocene Alkun Formation of central and western Ciscaucasia were studied in the following sections: the stratotype section on the Alkunka River, the Republic of Ingushetia; stratotype of the Caucasian Regional Stage on the Kuban River, Karachay-Cherkessia; Lower Miocene reference section on the Belaya River, Adygea; and in the sections of the Alkun Formation stratotype area on the Fiagdon and Mairamadag rivers, North Ossetia. Planktonic foraminifers in the Alkun Formation were studied for the first time. The available results made it possible to reveal the composition and structure of nannofossil and planktonic foraminiferal assemblages from the Alkun sediments in Ciscaucasia, to refine their stratigraphic and correlation potential and to recognize bionomic conditions of the Alkun basin in the studied area. As a result of the nannoplankton study the Cyclicargolithus floridanus Beds were recognized in the Alkun Formation and, taking into account the occurrence of the zonal species Triquet-rorhabdulus carinatus along with Tr. milowii, they are correlated with the upper (Miocene) part of the Aquitanian Zone NN1. Planktonic foraminiferal data permitted to recognize the Streptochilus pristinum Beds.