Carbon and oxygen isotopic composition of Paleozoic carbonate deposits of the Pechora Sea

Research subject. Paleozoic carbonate complexes in the offshore area of the Timan–Pechora oil and gas basin. Aim. To evaluate the possibility of using data on the isotopic composition of carbon and oxygen in carbonate rocks for the interpretation of depositional environments and stratigraphic correlation of geological sections. Materials and methods. Within the framework of the RN-Shelf-Arctic LLC (RNSHA) regional projects focused on a geological study of offshore areas, the isotopic composition of carbon and oxygen of Paleozoic carbonate deposits from the core of five wells were analyzed. Results. The value of δ 13 C carb increases up the section from -5.9‰ in S 2 to 6.0‰ in P 1 a-s. The most significant weighting of δ 13 C carb from -1 to 6‰ occurred in the Upper Carboniferous interval. The variations of δ 18 O carb from 23 to 33‰ are characterized by the absence of a general trend along the section combined with more frequent and abrupt excursions, which are most pronounced in the Carboniferous. Discussion and conclusion. Four local factors of isotopic variations were considered, including mineral, facial, post-sedimentary, and stratigraphic. Two of them – depositional environments and secondary (postdepositional) changes – are regarded as the major factors, being controlled in varying degrees on different stages by either local or global factors. The final result of their influence was integral and expressed by the “stratigraphic” curve of isotopic composition variability.