Organic Matter of Domanik Deposits of the Timan–Pechora Basin: the Oil Window Conditions

—A comprehensive study of Domanik deposits of the Timan–Pechora Basin has been carried out. The examined composition of hydrocarbon biomarkers, chemical structure of kerogen, carbon isotope composition, and rock lithology, the Rock-Eval pyrolysis data, and the contents of bitumen and Corg in the rocks give an insight into the geochemical processes in the oil window in the Domanik deposits, which took place at Tmax = 435–450 °C. The bitumen coefficient βCB is maximum in this temperature interval, reaching 30%. The obtained data on the distribution of polycyclic biomarkers in the Domanik rocks and the bitumen and Rock-Eval pyrolysis data allowed determining the boundary values of biomarker maturity coefficients in the study of the maturation of organic matter of the rocks. The carbon isotope composition of bitumen fractions in the Domanik rocks is considered, and the bimodal distribution of the δ13C values of the bitumen is shown.

The Shirokoe Place as a reference section of the upper Visean substage in the Upper Pechora basin (Unya river, Northern Urals)

Research subject. Carbonate rocks in the “Shirokoe Place” section (Unya River, Northern Urals). Material and methods. The work was based on a study of the composition and structural peculiarities of rocks and species diversities of forami- nifera and calcareous algae in the most important section of Upper Visean sediments in the lower reaches of the Unya river.Results. The rocks in the section are represented by bioclastic limestones, dolomites and various transition differences. The section features a wide presence of green Koninckopora, red Epistacheoides and Ungdarella algae. Less common are Palaeoberesella, Anthracoporella, Kamaena and Stacheoides. Fasciella is extremely rare, and Calcifolium is virtually absent. Foraminifera complexes are representative, but there are no zonal species Eostaffella tenebrosa (Venevsky horizon), genera Valvulinella (Tula horizon), Bradyina and Howchinia (Mikhailovsky and Venevsky horizons). Endothyranopsis, Janischewskina and Cribrospira are rare.Conclusions. The study of the species diversity of foraminifera and calcareous algae allowed us to clarify the stratigraphic division of the upper Visean sediments in the “Shirokoe Place” section. The Tula, Aleksinsky, Mikhailovsky and Venevsky horizons of the Upper Visean were reliably identified. The studied section can be used as a reference when creating stratigraphic schemes of Later Visean deposits for the Western subzone of the Upper Pechora transverse sinking of the Western folded zone of the Urals and adjacent areas of the PreUrals regional trough.

Early-Middle Frasnian (Late Devonian) carbon isotope Event in the Timan-Pechora Basin (Chernyshev Swell, Pymvashor River section, North Cis-Urals, Russia)

Details of the Early-Middle Frasnian boundary interval of the Pymvashor River section (Timan-Pechora Basin, Cis-Urals, in the far north of European Russia) are revealed by biostratigraphically constrained carbonate (δ13Ccarb) and organic carbon (δ13Corg) stable data. The studied interval corresponds to the lower part of the Domanik Formation, which consists of interbedded limestone and shale beds. Organic-rich black shale that lacks bioturbation and benthic organisms indicates an oxygen-depleted depositional environment. Detection of isorenieratene derivatives in organic matter indicates that anoxia was present in the photic zone during deposition. The Pymvashor River section contains δ13Ccarb and δ13Corg isotope records related to the Early-Middle Frasnian isotope Event. The similarity between the Cis-Uralian (this study) and the Chinese δ13Ccarb and δ13Corg oscillations, including the twostep pattern of the recorded major positive excursions, suggests a robust correlation of the Late Devonian Early- Middle Frasnian isotope Event and minor intra-event excursions. Magnitude of variations and values of δ13Corg and δ13Ccarb in the punctata Zone in the Pymvashor River section are minor than those observed in the North American, Polish, and Chinese successions. Such difference may reflect specific variation of the local environments.