Carbon isotopic composition of lower Paleozoic oils in the northern part of the Timan-Pechora basin

The carbon isotope composition of different in polarity fractions and individual n -alkanes of Lower Paleozoic oils in the northern part of the Timan-Pechora basin, showing geochemical signs of an organic matter of Ordovician age, formed by the remains of the problematic Gloeocapsomorpha prisca (G. prisca) alga, was studied. It is shown that the carbon of all fractions of the studied oils has a relatively light isotopic composition of about -31.5 d13C on average, which is significantly lower than the carbon of previously studied Upper Devonian oils genetically related to Domanik deposits. The carbon isotope profiles of the n -alkanes of the studied oils do not have pronounced anomalies, only for the C17 hydrocarbon, a slightly depleted in heavy carbon isotope is observed, n -C19 is not distinguished by carbon isotopic composition from the neighboring even homologues. The data obtained are compared with previously published data for oil of the basins of Illinois (USA) and Canning (Australia) similar in Ordovician G. prisca origin. It is shown that the isotope profiles of n -alkanes of the Ordovician oils of these two basins differ in contrast, and the data on the Timan-Pechora basin oils are closer to those of Australia than the United States ones.