Isotopic composition of carbon and oxygen in Upper Carboniferous-Lower Permian carbonate rocks of the Losinoostrov Formation (Subpolar Urals, Kozhim River)

The Paleozoic section on the Kozhim River of the Subpolar Urals is the best sequence of the northern Urals. The border of Carboniferous-Permian deposits are observed on the opposite banks of the Kozhim River and are represented by two types of sections: on the right bank — the Kozhym skeletal mound, on the left bank — depression deposits of mixed composition (Losinoostrov Fm.). The article presents the first information on the isotopic composition of carbon and oxygen in the Lower Permian limestones of the Losinoostrov Fm. It is shown that the obtained data on the isotopic composition on the 13C–18O diagram are visually separated into three clusters. The first cluster with the lowest values of 13C (–0.3…1.1 ‰) and 18O (23.5…25.0 ‰) included the most intensively silicified rocks (siliceous bioclastic limestones, secondary silicitolites, siliceous-carbonate-argillaceous mixtolites and siliceous-argillaceous limestone). The third cluster, with the highest values of 13C (3.9…5.1 ‰) and 18O (26.0…26.8 ‰), includes bioclastic and peloid-micritic limestones. In this case, the 13C values correspond to the range of variations in the carbon isotopic composition indicated in review works on the chemostratigraphic correlation of Permian deposits. The second cluster occupies an intermediate position and is characterized by the values of 13C (2.0…2.8 ‰) and 18O (24.3…25.4 ‰). This cluster is predominantly represented by limestones enriched with terrigenous materials. A comparison is made of the isotopic composition of the limestones of the Losinoostrov Formation with the coeval limestones of the Kozhim skeletal mound, which showed higher values of 13C and 18O in the latter.