Permian Non-Marine Bivalve Fauna From Continental Deposits Of The Dvina-Mezen Basin

Four stages (Urzhumian-Early Severodvinian, Late Severodvinian, Terminal Severodvinian-Early Vyatkian, Late Vyatkian) are established in the evolution of Permian non-marine bivalve fauna from continental deposits of the Dvina-Mezen Basin. The definition of the stages is based on the synthesis of data on the centers of taxon origin, according to their stratigraphic and geographical distribution. It is assumed that disappearance of Angarian non-marine bivalves is correlated to relative warming, as evidenced by the general direction of the positive excursions of carbon and oxygen isotopes on the isotope curves.