Geophysical processes and biosphere: article

Аnnotation: The presence of isotopically heavy carbon dioxide (CO2) in gases of hydrocarbon (HC) accumulations and mud volcanoes (MV) of the South Caspian Basin (SCB) served as a starting point for studying the distribution of a similar phenomenon in other sedimentary basins. The paper summarizes a large set of data from long-term geochemical studies in different regions of the world. The global distribution of isotopically heavy CO2 in basins of various tectonotypes, both in traditional and non-traditional hydrocarbon systems, has been established. The identity of the processes involved in its formation was revealed. Secondary methanogenesis is the most common phenomenon leading to enrichment of CO2 with the heavy isotope 13C with possible subsequent transformation. The formation of isotopically heavy CO2 is assumed in the depth interval of up to 2000 m. However, under certain geological and tectonic conditions, its presence at greater depths is possible. In the South Caspian Basin, positive CO2 in gases of HC accumulations and MV is predominantly formed in a closed/partially closed system under conditions of unbalanced metanogenic biodegradation.