The Research On Ginkgophytes Fossils From The Middle Jurassic In Baojishan Basin, Gansu Province

The ecological environment topics caused by the emission of greenhouse gases such as CO₂ have become one of the focuses of the world.As the indicator of climate and environment change,the plants inevitably recorded important information about climate change of geological time during their evolution.Therefore,the study on fossil plants possess important guiding significance to better predict the changes of global atmospheric CO₂ concentration.As one of the three major coalmine regions in Gansu Province,the Jurassic strata develop widely and contains abundant plant fossils in coal-bearing strata.The thesis takes Ginkgopsida and Czekanowskiopsida fossils as material which from the Middle Jurassic Yaojie Formation in Baojishan Basin,Gansu Province.According to the leaf morphology and epidermal structures,they can be assigned to one Genus two species of Ginkgopsida: Ginkgoites obrutschewii Seward,Ginkgoites cf.sibiricus?Heer?Seward;two Genus three species of Czekanowskiopsida: Czekanowskia?Vachrameevia?shiguaiensis,Phoenicopsis angustifolia Heer,Phoenicopsis speciosa Heer.Among of them,Czekanowskia?Vachrameevia?shiguaiensis is the first discovery in the basin.In thesis cuticle structures of Phoenicopsis angustifolia Heer?Czekanowskia rigida Heer ? Czekanowskia?Vachrameevia?shiguaiensis and Ginkgoites cf.sibiricus?Heer?Seward were investigated in detail.Based on the above research,the paleoatmospheric CO₂ level of the Middle Jurassic Baojishan Basin is reconstructed by the stomatal ratio method,its numerical value is 1.55×10-3,The result is closer to the best fitted curve of the GEOCARB? carbon balance model.Therefore,Czekanowskialean might be a good index material for reconstructing paleoatmospheric CO₂ level.For the relation between palaeoatmospheric CO₂ and temperature increment?? T=4.0×lnR?CO₂??,according to the RCO₂ value in thesis,the temperature increment is 6.6?,the temperature is about 15.5? at that time,indicating that Baojishan Basin stayed in high temperature conditon that of extant in the Middle Jurassic.In addition,the results of cuticle structures show that cuticles are generally thin,in the nature of rare papillamastoid or trichome,stomatal sink slightly;all characteristics indicate that the fossil plant existed in relatively warm and humid paleoclimate.The deduction coincide with the warm and humid paleoclimate status in the Middle Jurassic which is considered according to the fossil flora contains mainly dominated Ginkgophytes?Ginkgopsida and Czekanowskiopsida?,and the minor proportion of Filicopsida,Sphenoposida and Coniferopsida,least Cycadopsida in the Baojishan Basin.And the paleoenvironment was suitable for the prosperity and development of fossil plants of studied region in those days.