Stratigrafiâ. Geologičeskaâ korrelâciâ

Lithological, paleontological and Rb–Sr isotope-geochronological studies of the Upper Vendian deposits of the borehole Kepina-775, drilled in the north-west of the Mezen Syneclise of the East European Platform (South-Eastern White Sea region), were carried out. Redkinian biota were found in the Verchovka and Zimnegory beds of the Ust-Pinega Formation. Transit associations of microfossils have been established in the Arkhangelsk beds of the Ust-Pinega Formation and in the “Mezen” Formation. The Kotlin Regional Stage is not recognized according to biostratigraphic data in the South-Eastern White Sea region. 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 obtained as 565 ± 9 Ma. The presence of an insignificant admixture of detrital 2M₁ illite allows us to consider the obtained dating 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.

Conglomerates are widespread in the Paleozoic sediments of Wrangel Island and occur at different stratigraphic levels of the sedimentary cover. The conglomerates of the Central tectonic zone of Wrangel Island previously classified as Carboniferous are represented by two types, which differ in the composition of their components. Conglomerates of the first type are complexly constructed, fragments of metamorphic shales and basic volcanic rocks dominate their composition. Rounded quartz fragments, limestone fragments and faunal remains dominate the conglomerates of second type. Their composition is analogous to that of intraformational conglomerates from sections of the Northern tectonic zone. The age of these conglomerates can reliably be established through the analysis of faunal remains, which indicate a Guadalupian–Lopingian (Middle–Late Permian) age. Thus, conglomerates of the first and second types in the Central zone of Wrangel Island are most likely of different ages, while the later (conglomerates of the second type) can be attribute to the Middle–Upper Permian. Two horizons of conglomerates of different ages in the Central zone of Wrangel Island indicate local rearrangements at the beginning of the Pennsylvanian (the Bashkirian age) and Guadalupian–Lopingian. Similar unconformities can also be in coeval sediments of Sverdrup basin.

Boreal radiolarians of the Upper Jurassic (Oxfordian, Kimmeridgian and Volgian) and of the lower part of Lower Cretaceous (Riazanian and Valanginian) of Russia are known from the territories of Eastern European Craton, Timan-Pechora Basin, Western Siberian Basin and northern periphery of the Siberian Craton. Radiolarian assemblages of this stratigraphic interval are characterized by domination of high-latitude taxa (genera Parvicingula and Praeparvicingula of the family Parvicingulidae) and common presence of typically boreal family Echinocampidae (genera Echinocampe, Nordvikella and Arctocapsula). Genus Pantanellium is present in the Kimmeridgian of Eastern European Craton and Timan-Pechora Basin. This genus is represented by group of species P. meraceibaense, that can penetrate to southern boreal areas. Previous conclusions of the presence of subfamily Vallupinae, which is typical for low paleolatitudes, cannot be confirmed. Radiolarians assemblages of the boreal Upper Jurassic and lower part of Lower Cretaceous display considerable taxonomic changes upwards in the sections, therefore they can be used in stratigraphy.