Abstract— <p>Lithological, paleontological and Rb–Sr isotope-geochronological studies of the Upper Vendian deposits were carried out in the Kepina-775 Borehole, drilled in the north-west of the Mezen Syneclise of the East European Platform (South-Eastern White Sea region). The Redkino biota was found in the Verkhovka and Zimnegory Beds of the Ust-Pinega Formation. Transit microfossil associations are established in the Arkhangelsk Beds of the Ust-Pinega Formation and in the “Mezen” Formation. The Kotlin Regional Stage is not recognized in the South-Eastern White Sea region using biostratigraphy. The presence of Ediacaran soft-bodied organisms in the Erga Beds, as well as the inherited nature of the distribution of microfossils coming from the Ust-Pinega Formation, make it possible to expand the stratigraphic interval of the Redkino Regional Stage to the base of the Mela Beds. The age of the Mela Beds has not been reliably determined. The Rb–Sr age of the generations of authigenic 1M illite extracted from the mudstones of the Arkhangelsk Beds of the Ust-Pinega Formation was determined as 565 ± 9 Ma. The presence of an insignificant admixture of detrital 2M₁ illite allows the obtained dating to be considered as the lower age limit of the accumulation of the Arkhangelsk Beds. The Rb–Sr age of the “fine-grained” generations of 1M_d illite (about 540–460 Ma) corresponds to the stage of burial diagenesis of the clayey sediment.</p>