Biostratigraphical subdivision of the Kokurino section (Saratov Region) and insights into stratigraphy of the Campanian of the Middle Volga Region

An interval of the Upper Campanian siliceous-carbonate rocks in the Kokurino section (in the vicinity of Saratov) has been found to contain an Upper Cretaceous assemblage of ammonites and echinoids previously unknown from the Saratov Volga Region. Occurrence patterns of the above groups have been studied alongside with those of belemnites, bivalves, gastropods, brachiopods, sponges, benthic and planktonic foraminifers, radiolarians, dinocysts and calcareous nannoplankton. Biostrata have been compared and correlated in terms of all paleontological groups listed above. Stages of the development of the paleontological groups have been studied during the Campanian of the Middle Volga Region. Lithology and biota peculiarities make it possible to regard the examined section as the stratotype of the proposed Upper Campanian lithostraton from the Saratov Volga Right Bank Region – the Kokurino Beds. The paper deals with the problem of boundary diachroneity in the conventional Campanian formations in the Volga Region – the Pudovkino, the Rybushka and the Ardym ones