Upper Campanian–Maastrichtian Planktonic Foraminifera of the Eastern European Palaeobiogeographic Province

Planktonic foraminifera are a key tool for Upper Cretaceous biostratigraphy in pelagic basins of the Tethyan Realm. This study provides an analysis of planktonic foraminiferal assemblages from the upper Campanian–Maastrichtian of the eastern European palaeobiogeographic province. Detailed sampling of natural outcrops in Crimea and the northwestern Caucasus yielded more than 300 washed micropaleontological residues. Biostratigraphic calibration is supported by ammonites, belemnites, calcareous nannoplankton, benthic foraminifera, ostracods, and dinocysts. The stratigraphic interpretation integrates with magnetostratigraphic and stable isotope data. In southwestern Crimea, the Beshkosh, Chakhmakhly, and Belbek reference sections were studied. The sedimentological model is close to a distally steepened ramp. The outer ramp is represented by foraminiferal to calcispheric mud–wackestones, whereas the upper part consists of mixed terrigenous–carbonate mid–ramp facies or transitional to lower shoreface facies. Planktonic foraminiferal assemblages are dominated by biserial and triserial taxa, with rare globotruncanids. The Laeviheterohelix glabrans Beds were established for the uppermost Campanian – lower Maastrichtian interval, and the Guembelitria cretacea Beds for the upper Maastrichtian in the Beshkosh and Chakhmakhly sections. The occurrence of Contusotruncana morozovae(Vassilenko) in the Belbek section allows recognition of the C. morozovae Acme Zone (Maslakova, 1967) and its correlation with the L. glabrans Beds. In the Beshkosh section, the FO of Gu. cretacea Cushman approximates the base of Chron C30r. Benthic foraminifera indicate erosion at the Campanian–Maastrichtian boundary and in the uppermost Maastrichtian. In eastern Crimea, Maastrichtian deposits are exposed in the Klementyev Mountain reference section. The basal part correlates with the L. glabrans Beds of southwestern Crimea. The main outcrop comprises muddy basinal to upper slope mud-wackestones, overlain by mixed terrigenous–carbonate deposits represented by alternating sandy wackstones and sandstones of lower- to mid-ramp. Two standard zones are identified: the Abathomphalus mayaroensis Interval Zone and the Pseudoguembelina hariaensis Interval Zone. The FO of Ps. hariaensis Nederbragt lies close to the base of the calcareous nannoplankton Zone CC26b. A hiatus within the Plummerita hantkeninoides Interval Zone is supported by nannoplankton data. In the northwestern Caucasus, Campanian deposits of the Podkumok-Lake section consist of mixed terrigenous–carbonate calcispheric to foraminiferal–calcispheric silty wacke-packstones of lower ramp of mid-shelf facies. The C. morozovae Zone is characterized by abundant large, moderately preserved globotruncanids, especially Contusotruncana contusa (Cushman). Upper Campanian ammonites Pachydiscus (P.) subrobustusSeunes provide additional biostratigraphic control. In the Bugunta section, Maastrichtian deposits are represented by mixed terrigenous-carbonate calcispheric to foraminiferal-calcispheric sandy wacke–packstones of lower ramp of upper–shelf facies. The lower part of the A. mayaroensis Zone correlates with the Mid-Maastrichtian carbon isotope event. The integrated stratigraphic data reveal significant hiatuses at the Campanian/Maastrichtian boundary and within the upper Maastrichtian. Facies-controlled assemblage variability requires combined use of heterohelicid- and globotruncanid-based zonations for reliable regional correlation. The study was supported by the Russian Science Foundation Grant No. 25-77-10106, https://rscf.ru/project/25-77-10106/.