Study On Equisetaleans And Ginkgoaleans Fossils And Its Paleoenvironment Implications From Early And Middle Mesozoic Of Baojishan Basin,Gansu Province,China

Baosjishan basin is situated in Pingchuan,Baiyin City,Gansu Province,China,where contains Mesozoic formations,such as the Late Triassic Nanying'er Formation and the middle Jurassic Yaojie Formation.Abundant plant fossils were reported in the both Formations.Although due to bad preservation,micro-level studies on fossil plants from Nanying'er Formation have not been published yet.In this thesis,one species of Ginkgoales,Sphenobaiera sp.and two species of Equisetales,Schizoneura africana and Equicalastrobus pusillus L.Zhang et D.F.Yan sp.nov.from the Late Triassic Nanying'er Formation were reported.The situ-spores of E.pusillus sp.nov.were also obtained.So far,the evolutionary pathways of Equisetales during geological period is still controversial,there is no common view accepted widely for that.E.pusillus sp.nov.reported here own relatively similar features to modern Equisetum in spores and size,compared with the type species,E.chinleana.Given the characteristics of E.pusillus sp.nov.,we suggest that it might be a link in the evolutionary pathways of Equisetales from Equicalastrobus to Equisetum.The outer layer of a plant,the epidermis,is a multifunctional tissue that plays an important role in controlling the exchange of water,gas,and nutrients with the living environment.In this thesis,we disscussed the 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 analysis indicates that the L/W ratios of Ginkgo biloba pavement cells are negatively correlated with MAT,MAP,and RH,and linear regression equations can be established.Based on these equations,paleoclimatic parameters were inferred using the fossil data of ginkgoaleans from the Middle Jurassic and the Late Triassic.The reconstruction results show that MAT,MAP and RH is 13.2?,710.3 mm and 74%respectively in the Middle Jurassic,Baojishan basin;is 13.3?,721.2 mm and 74%respectively in the Late Triassic,Huating region.The estimated paleotemperatures are consistent with the results of the currently used stomata ratio method and the global CO₂ prediction model which indicate the L/W ratio method discussed here is a new approach to region paleoclimate.