Middle Coniacian-Santonian foraminiferal bioevents around the Mangyshlak Peninsula and Russian Platform

The distribution of foraminifers and some macrofossils at the Coniacian/Santonian boundary in four selected sections, two on the Mangyshlak Peninsula (West Kazakhstan) and two on the Russian Platform, are compared in this paper. The first occurrence (FO) of Cladoceramus undulatoplicatus (F. Roemer) is the primary marker for the boundary in the Mangyshlak area. Specimens of the Sphenoceramus pachti-cardissoides group occur at the base of the Santonian on the Russian Platform. This is the equivalent to the "Sphenoceramus Teilzone", which characterizes the Coniacian/Santonian boundary interval in Germany. Benthic foraminifers predominate around the boundary in both Mangyshlak and on the Russian Platform and may be used as secondary markers. The following bioevents were recognised close to the boundary in these areas: (1) abundant Stensioeina emscherica (Baryschnikova), the simultaneous FO of Gavelinella vombensis (Brotzen), and the FO of G. thalmanni (Brotzen); (2) the last occurrence (LO) of G. thalmanni (Brotzen); (C) the FOs of Neoflabellina suturalis suturalis (Cushman) and Stensioeina exculpta exculpta (Reuss); and (4) the FO of rare N. gibbera (Wedekind) just below the FO of Cladoceramus undulatoplicatus (F. Roemer).