Calcareous nannofossils and other proxies define the Santonian–Campanian boundary in the Central Crimean Mountains (Alan-Kyr section)

The taxonomic composition and detailed stratigraphic distribution of the calcareous nannofossils from the Santonian and Campanian of the Crimea have been studied for the first time. The identified assemblage of calcareous nannofossils in the Alan-Kyr section consists of 85 species, including all primary and additional zonal markers. The following calcareous nannofossil zones and subzones have been recognised and correlated with planktonic (PF) and benthic (BF) foraminifera zones: transitional Santonian–Campanian CC17 or latest Santonian UC13 (Dicarinella asymetrica/D. concavata PFZone and the lower part of Globotruncanita elevata/stuartiformis PFZone), lower Campanian CC18a/UC14a, CC18b–c and CC19/UC14b–UC15a (Globotruncanita elevata/stuartiformis PFZone), lower Campanian CC20/UC15b (Contusotruncana plummerae/Globotruncana ventricosa PFZone), upper Campanian CC21/UC15c (Contusotruncana plummerae/Globotruncana ventricosa PFZone and Globotruncanella havanensis PFZone) and upper Campanian CC22/UC15d (Globotruncanella havanensis PFZone). Using magnetostratigraphic data as the primary source for definition of the base of the Campanian, we place the Santonian–Campanian boundary in the Alan-Kyr section at the level of the base of Chron C33r and inside the nannofossil transitional Santonian–Campanian CC17 or lower Campanian UC14 Zone and the planktonic foraminifera Santonian D. asymetrica/D. concavata Zone. This conclusion is supported by the relative position of other microfossil bioevents: the first occurrence of Broinsonia parca parca, which happens just above the highest occurrences of both Dicarinella asymetrica and D. concavata, as well as the lowest occurrence of the benthic foraminifera Neoflabellina asema.