Microfauna, Palynomorphs, and Biostratigraphy of the Upper Bajocian Strenoceras niortense Zone (Middle Jurassic) of the Kuban River Basin, Northern Caucasus

Abstract

Microfossils of the Strenoceras niortense Zone of the Upper Bajocian of the Karachay-Cherkessian Republic are studied. The zone is represented mainly by dark gray silty-sandy clays, with scattered nodules often arranged in interbeds, and belongs to the lower part of the upper subformation of the Djangura Formation. The taxonomic composition and distribution of foraminifera, ostracods, dinoflagellate cysts, and miospores in the section has been identified. The ranges of biostratigraphic units based on foraminifera, ostracods, and dinocysts are emended and these units are correlated with the ammonite scale. The distribution of benthic foraminifers indicates that these are Beds with Ophthalmidium caucasicum, comparable with the entire Niortense Zone and most of the Garantiana Zone. The Beds with Globuligerina dagestanica established using planktonic foraminifera are correlated with the entire studied interval from the Niortense Zone to the Lower Bathonian, inclusive. In the middle-upper part of the Niortense Zone (Rostovtsevi and Baculatum Subzones), the Beds with ostracods Palaeocytheridea (Malzevia) subtilis were recognized for the first time. The beds with dinocysts Carpathodinium predae, Rhynchodiniopsis? regalis, Meiourogonyaulax valensii are correlated with the range of the Niortense and Garantiana Zones and the lower part of the Parkinsoni Zone, inclusive. Characteristic taxa of microfauna and dinocysts are illustrated.