Reading paleoenvironmental information from Middle Jurassic ginkgoalean fossils in the Yaojie and Baojishan basins,Gansu Province,China

A new method for reconstructing paleoenvironments using the pavement cell characteristics of Middle Jurassic ginkgoalean fossils from the Yaojie and Baojishan basins, Gansu Province, China, is presented. Specifically, we use present-day relationships between the length-to-width (L/W) ratio of leaf pavement cells of Ginkgo biloba and mean annual temperature (MAT), mean annual precipitation (MAP), and relative humidity (RH). Primary analyses indicate that the L/W ratio of Ginkgo biloba pavement cells is negatively correlated with MAT, MAP, and RH, and linear regression equations can be established. Based on these equations, paleoclimatic parameters were inferred using the ginkgoalean fossil data. The estimated paleotemperatures in the Yaojie and Baojishan basins during the Middle Jurassic are approximately 6 °C higher than those of the present day, which is consistent with the results of the currently used stomata ratio method and the global CO₂ prediction model. We deduce that paleoprecipitation in the basins was approximately 460 mm higher and paleohumidity approximately 20% higher than current conditions and thus the two basins exhibited humid subtropical conditions during the Middle Jurassic. Fossil flora and spore-pollen assemblage data from the study areas corroborate the new observations.