Testing multiple pCO2 proxies from the Lower Cretaceous of the Laiyang Basin, eastern China

Abstract

In recent decades, several proxies have been developed to reconstruct atmospheric palaeo-CO2 concentrations (pCO2). The confidence in pCO2 estimates can be increased by comparing results from multiple proxies with multiple species at a single site. Here, we develop a new pCO2 record for the Hauterivian–Barremian using three distinct proxies applied to two fossil coniferous species (Cupressinocladus sp. and Brachyphyllum obtusum) collected from Laiyang Basin, eastern China. The pCO2 values were 579–663 ppmv (recent standardization) and 966–1106 ppmv (Carboniferous standardization) based on the stomatal ratio (SR)-based method, and 472–525 ppmv based on the mechanistic model. All the pCO2 values calculated by these two methods here were highly coincident with those reconstructed by other SR-based and geochemical methods during the early stage of the Early Cretaceous. The pCO2 value estimated using the carbon isotope model was 202–409 ppmv, which is generally lower than the pCO2 value estimated using the other methods. The comparison and discussion of the results and theoretical mechanism from these three proxies indicate that the mechanistic model may be more feasible when used to reconstruct the pCO2 in the geological period. Furthermore, compared with data from other pCO2 records in the Early Cretaceous, the pCO2 values obtained in this study indicate a relatively low atmospheric CO2 concentration during the Hauterivian–Barremian and reflect the cooling climate in the early stage of Early Cretaceous.