The albian-cenomanian boudary in the northern part of the Don-Medveditsa dislocations. Paper 1. The history of studying and the section descriptions

The Albian-Cenomanian rocks compose a single complex of terrigenous deposits over the Volga Region. Delineation of the boundaries of the Cretaceous system units generally tends to cause difficulties, accounted for by rare finds of the fossils. In the northern part of the DonMedveditsa dislocations, natural outcrops of the Albian and the Cenomanian beds in the Burluk river valley have been examined since the 1950s. The authors have earlier made some case studies on the Gordienki, Krasny Yar, Melovatka and Moiseyevo sections. Within the subsequently identified Miroshniki site, the paleontologically characterized phosphorite and sandstone interlayers have been specified for the first time in the boundary interval of the Albian and Cenomanian beds. The history of studying the Albian-Cenomanian stratigraphy of the Ilovlya-Medveditsa apex of the Don-Medveditsa swell is presented. The structure of the Albian-Cenomanian boundary intervals within the Melovatka-5, -6 and Miroshniki has been considered.