CO2 levels in the Late Palaeozoic and Mesozoic atmosphere from soil carbonate and organic matter, Satpura basin, Central India

A number of calcic palaeosols have been identified within the fluvial deposits of the Motur (Permian), the Denwa (Triassic), the Bagra (Jurassic) and the Lameta (Cretaceous) Formations of the Satpura sedimentary succession, Central India. These palaeosols show accumulation of pedogenic carbonates in rhizocretions and glaebules. The carbon isotopic compositions of these carbonates and the coexisting soil organic matters are used to determine the isotopic composition and the partial pressure of atmospheric CO₂ using the CO₂ palaeobarometer developed by Cerling Am. J. Sci., 291 (1991) 377]. It is seen that the atmospheric CO₂ level increased by a factor of 8 from the Permian to the Jurassic and declined again during the Cretaceous. The nature of the changes agrees with the result of the CO₂ evolution model of Berner (GEOCARB II) but the magnitude of the CO₂ increase in the Middle Jurassic and the Late Cretaceous was higher than the predicted value. Degassing of Earth's interior due to rapid break-up of the Gondwana landmass during the Triassic and Jurassic period could have caused the rapid CO₂ increase.