Palaeoenvironmental implications of Baiera hallei Sze from the Middle Jurassic in Shaanxi Province, China

Terrestrial plants are important indicators of palaeoclimate and palaeoenvironment during the geological history. The Ginkgoales leaves are commonly used to reconstruct the atmospheric palaeo-CO 2 concentration ( p CO 2 ) during the Jurassic. Baiera , a genus of Ginkgoales, however, has been less reported in the reconstruction of the p CO 2 during the Middle Jurassic . In this paper, Baiera hallei Sze from the lower Middle Jurassic (Aalenian) Yan’an Formation in the central Ordos Basin is studied in detail based on abundant materials. Ten well-preserved leaves of B . hallei were selected to calculate stomatal parameters, and their stomatal index was used to estimate the p CO 2 . The average SI was 6.19 ± 0.38, the p CO 2 obtained by the stomatal ratio method was 1121 ± 73 ppm, and the average palaeotemperature reconstructed by McElwain’s empirical formula was 13–15.8°C. The p CO 2 roughly coincides with the long-term carbon cycle model GEOCARB II. The palaeoclimate in Yulin district was warm and humid during the Aalenian (early Middle Jurassic).