Middle Oxfordian–Lower Kimmeridgian Calcareous Nannoplankton and Foraminifers in Ivanovo Oblast, European Part of Russia

Abstract

Middle Oxfordian–lower Kimmeridgian calcareous nannoplankton and foraminifers were first studied from the core log of the well drilled in Ivanovo oblast. Nannoplankton is well preserved; in total, nearly 25 species were identified. Zone NJ15 was distinguished on the basis of nannoplankton. Coccoliths of representatives of the genus Watznaueria, which are mostly cospomopolitan species, are dominant quantitatively. A sharp prevalence of W. britannica coccoliths indicates unstable habitat conditions in near-surface waters and their mesotrophy. Foraminifers typical of the Opthalmidium strumosum–Lenticulina brestica and Lenticulina kuznetsovae–Epistomina praetatariensis zones were studied as accompanying microfauna for substantiation of the age of country deposits.