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Research subject. This article focuses on the geological structure of the northern part of the Pai-Khoi carbonate parautochthone.Materials and methods. The study was based on the data obtained on the key sections of the North-Western Pai-Khoi. Research methods included lithological and facies analysis, subsidence curves, reconstruction of the thermal maturity of deposits based on conodont alteration indexes, X-ray microtomography for determining porosity values.Results. The Upper Devonian–Carboniferous succession (ca. 900 m thick) is composed of the terrigenous and carbonate Pyrkov Fm. (Frasnian), carbonate Lymbadyakha Fm. (Famennian-Tournaisian), Bolvanskii Fm. (Visean-Bashkirian), and Hoiponganase Fm. and Reef Chaika (Moskovian-Kasimovian). The early Frasnian part of the succession was deposited in a shallow-water environment. In the Middle–Late Frasnian, the Korotaikha paleodepression and an isolated carbonate platform was formed on the shelf edge. Filling of the paleodepression was completed at the end of the Early Visean. In the Late Visean–Late Carboniferous, a carbonate platform (ramp) formed. A Middle Paleozoic paleogeothermal gradient reconstructed on the basis of conodont alteration indexes is much higher in the Pai-Khoi carbonate parautochthone than in the most of Pechora Plate regions. This is likely to have been caused by the tectonic activity of the plate border in the Late Carboniferous–Mesozoic. A downward decrease in open porosity (from 6% to 0.1%) is likely to have been associated with increased compaction and recrystallization of the carbonates.Conclusions. Famennian-Tournaisian carbonate formations of the Pai-Khoi carbonate parautochthone were deposited under the conditions of isolated platform environment; however, the Visean–Late Carboniferous deposits were formed in the outer ramp environment. The Late Devonian–Middle Carboniferous carbonate deposits of the Pai-Khoi parautochthone demonstrate an extremely low open porosity and a high thermal maturity. These properties, along with the pronounced faulting and folding of the rocks, significantly decrease petroleum-bearing prospects of these deposits.

Research subject. The article considers the Famennian‑Tournaisian sequence of the South-Eastern part of the Tchernyshev Uplift (North Cis-Uralian). The sequence corresponds to the Izyayu Formation.Materials and methods. The article is focused on the clarification of the stratigraphy, composition and depositional environment of this formation. Research data about the Izyayu Formation in the type area (Izyayu River) were used. The stratigraphic framework of this study included data on conodonts, foraminifers and carbonate carbon isotopic shifts.Results. In the type area under study, the Izyayu Formation corresponds to the interval from the upper part of the Famennian (upper part of the Palmatolepis marginifera utahensis conodont Zone) up to the middle part of the Tournaisian (Lower crenulata conodont Zone). The formation is 100– 120 m thick. The Izyayu Formation grades to the upper part of the deep-water Syvyu Formation in the east, and to the shallow-water Kamenka Formation and the lower part of the Ydzhid Formation. The areal of the Izyayu Formation comprises the South-Eastern part of the Tchernyshev Uplift. The Formation was deposited in the environment of a gentle prograding slope of a carbonate platform.Conclusions. The Izyayu Formation in the type area is composed of thin clayey-carbonate graded cycles. It covers the stratigraphic interval from the Zelenets Regional Stage through the Tcherepet Regional Stage. This formation is easily distinguishable by lithological features in outcrops and borehole cores.