Magnetostratigraphy of the Danian Stage of the Volga Right Bank Region near Saratov. Article 2. Belogrodnya Formation–Lower Syzran Subformation

The present paper provides a detailed description of the stratotype of the Belogrodnya Formation, which, like the Klyuchevskaya Member, lies on the Upper Cretaceous eroded surface and is overlain by the Lower Syzran Subformation. The exact age relationships between the Klyuchevskaya Member and the Belogrodnya Formation have not been established to date. The paper presents for the first time magnetostratigraphic data obtained from nine studied sections of the Belogrodnya Formation and lower portions of the Lower Syzran Subformation and new results of nannofossil stratigraphy. Two normal and reversed polarity magnetozones are identified and the approximate level of the geomagnetic inversion C28n–C27r is substantiated. According to the magnetostratigraphic and micropaleontological data, the Belogrodnya Formation cannot be younger than NP3 nannofossil zone. Based on the results of detailed correlation of sections using lithological, magnetostratigraphic, geochemical data, materials of mineralogical analysis of thin sections, and information on the anisotropy of magnetic susceptibility, the structure of the Belogrodnya Formation has been clarified, the diachroneity of its boundaries has been established, and a petromagnetic criterion has been proposed to substantiate the upper boundary.