Upper Cretaceous nannoplankton zonation in North Bulgaria

Ten calcareous nannofossil zones are recognized in the sediments of so-called "North European" type of Upper Cretaceous in North Bulgaria: Quadrum gartneri Zone (Lower-Middle Turonian), Eiftellithus eximius Zone (Middle­-Upper Turonian), Lucianorhabdus maleformis Zone (Upper Turonian-Lower Coniacian), Micula staurophora Zone (Upper Coniacian-Lower Santonian), Reinhardtites anthophorus Zone (Lower-Upper Santonian), Zygodiscus spiralis Zone (Uppermost Santonian-Lowermost Campanian), Broinsonia parca Zone (Lower Campanian), Ceratolithoides aculeus Zone (Lower-Upper Campanian), Tetralithus trifidus Zone (Upper Campanian-Lower Maestrichtian) and Arkhangelskiella cymbiformis Zone (Lower Maestrichtian). These zones are established on the basis of the stratigraphic distribution of over 30 nannofossil species from the Turonian to the Maestrichtian. The photographs of the stratigraphically important species are made on SEM, TEM and LM.