STRATIGRAPHIC POSITION AND COMPREHENSIVE SUBSTANTIATION OF THE NEMAKIT-DALDYNIAN STAGE OF THE UPPER VENDIAN

Nemakit-Daldynian Stage was originally introduced as a regional stage, embracing the lowermost Cambrian strata with the oldest small shelly fossils, for the Anabar uplift sections in the 1960s. In subsequent years, it became widespread in the works of Soviet researchers as the terminal stage of the Upper Vendian series. Almost at the same time, the concept of the Manykaian stage appeared, which is close in its volume and geological meaning to the Nemakit-Daldynian Stage. Although this unit plays a crucial role for our understanding of the chronology of biotic turnovers at the Vendian–Cambrian transition, its status, age, and correlation with the Manykaian stage and units of the International Chronostratigraphic Chart (ICC) remain unclear. This study reveals the development of concepts regarding the stratigraphic volume and rank of the Nemakit-Daldynian Stage. The integrated biostratigraphic, stable isotope and geochronological data shows this unit belongs to the Upper Vendian series and spans the interval from the first appearance of unequivocal anabaritids (~539 Ma) to the first appearance of the Tommotian small shelly fossils (~530 Ma). In this interpretation, the Nemakit-Daldynian Stage corresponds to the Fortunian stage of the Cambrian System in the ICC. The base of this unit is coeval to the base of the Rovno regional stage of Baltica.