Early Cretaceous atmospheric pCO2 levels recorded from pedogenic carbonates in China

Pedogenic carbonates were collected from Early Cretaceous strata in Sichuan and Liaoning, China. These paleosol carbonates and calcareous paleosols were evaluated in order to reconstruct atmospheric CO2 concentrations during the Early Cretaceous using a paleosol barometer. Using the isotopic ratios of pedogenic carbonates from Early Cretaceous (early-middle Berriasian, early Valanginian) strata in Sichuan Basin, averaged atmospheric pCO2 is estimated to have been 360 ppmv in the early-middle Berriasian and a mean value of 241 ppmv in the early Valanginian. In the late Barremian in western Liaoning, however the average was 530 ppmv, with a range of 365 ppmv and 644 ppmv, lower than previous estimates of pCO2 for these time periods, consistent with the suggestion of overall climate cooling and paleotemperature fluctuation during the Early Cretaceous. This indicates that not all of the Cretaceous was a high or continuous CO2 greenhouse, especially during Early Cretaceous.