Early Cretaceous Cheirolepidiaceae From The Jiuquan And Liupanshan Basins And PCO₂ Estimates

Cheirolepidiaceae has a strong indication of the palaeo-climate.In this paper,the palaeo-climate and palaeo-environment were qualitative and quantitative studied based on the fossils of Cheirolepidiaceae collected from the lower Cretaceous?upper Aptian-upper Albian?of Jiuquan Basin in Gansu Province and Liupanshan Basin in Ningxia Automous Region.The paleo-atmospheric CO₂ concentrations?pCO₂?and its variation trends in the Zhonggou Formation?late Aptian-early Albian?of the Jiuquan Basin and the Naijiahe Formation?late Albian?in the Liupanshan Basin were reconstructed based on the leaf gas exchange mechanistic models,stomatal ratio method and carbon isotope model.The pCO₂ was 505-688 ppmv during late Aptian to early Albian and was 505-688 ppmv during the late Albian based on the leaf gas exchange mechanistic model.The pCO₂ of the Liupanshan Basin was 604-1007 ppmv during the late Albian based on the stomatal ratio method.The pCO₂ was 220-317ppmv during late Aptian to early Albian and 174 ppmv during late Albian based on the carbon isotope model.In addition,the morphology and the cuticular structures of Pagiophyllum combined with its fossil records of the Early Cretaceous and paleogeographic distribution,the palaeo-environment of the Jiuquan Basin during the late Early Cretaceous was qualitatively predicted.The pCO₂ results re-established by the leaf gas exchange mechanistic model are similar to the pCO₂ results re-builted by the recent standardization of the stomatal ratio method.While the pCO₂ results recovered by the carbon isotope model are generally lower than other two methods.Moreover,the pCO₂ recover by these three methods showed significant fluctuation during the late Aptian to late Albian,which may be related to the Greenhouse Warming,the Oceanic Anoxic Event?OAE1b?and Cold Snap Event during the late Early Cretaceous.