Late Pliocene atmospheric CO 2 estimates based on fossil leaves of Machilus (Lauraceae) in Yunnan, Southwest China

The fossil specimens from the late Pliocene Ciying Formation of Qujing Basin in Yunnan Province, southwest China are examined and used for reconstructing palaeo-CO2 level. These fossil leaves are characterised by their long elliptic shape, attenuate apex, entire margin, straight or moderately incurved primary vein. The leaf physiognomic and cuticular characteristics support these fossils assigned to the genus Machilus Nees, 1831 (Lauraceae Juss, 1789). Specifically, M. yunnanensis Lecomte, 1913 has an ecological setting and morphological structure that most resembles the fossil leaves and therefore is selected as the nearest living equivalent species (NLE). According to the stomatal ratio method, palaeo-CO2 was estimated as 414.38–483.11 ppm, which indicated an increasing trend during the mid-Piacenzian. Although CO2 levels based on different indicators showed different intensity of fluctuations, all the terrestrial and marine proxies indicated a peak CO2 value in the mid-Piacenzian, which was coupled with extreme warm climate during the period.