Ailanthus,Ulmus And Betula Fossils From The Oligocene Of Western Qaidam Basin And Its Significance

Located in the northeastern part of the Qinghai-Tibet Plateau,the Qaidam Basin is the largest inland basin on the plateau.since the Cenozoic uplift of the Qinghai-Tibet Plateau,it is one of the ideal areas for studying paleoclimate changes.Scientists have studied relevant scientific research work in the basin through magnetic stratigraphy,isotope stratigraphy and paleontology,and have achieved fruitful results.However,the geological information of fossil plants in this basin is relatively scarce.Recently,fossil fruits and leaves were found in the Oligocene Shangganchaigou Formation from the western Qaidam Basin.Through morphological study and comparison,the fossil fruits was identified as three species,namely Ailanthus confucii,Ulmus sp.,and Betula cf.microphylla.The leaves were identified as Ailanthus confucii.The fruit and leaf fossils of Ailanthus are the first report in the Qaidam Basin,and this study supported the view that the Ailanthus originated in India,we speculated that the Ailanthus spread northward through the Qaidam Basin;The discovery of fruit fossil of Ulmus provides fossil evidence for the origin and evolution of this genus,speculating that the Ulmus originated in North America,and the Oligocene has spread to the current study area;the friut fossil of Betula is the first report in the Qaidam area,enriching the birch wing The record of fossils.We investigated the living environment of the nearest living relatives species of current fossil plants,the current living environment and geographical distribution of the current fossils,and the characteristics of the paleoenvironment of the Oligocene in the study area are discussed.In comparison,the Oligocene may be a warm and humid environment with an average annual temperature of 0.4-15.5 °C,the hottest month average temperature of 9.5-28 °C,and the coldest monthly average temperature of-15.9-4.3 °C;annual precipitation 203-1358 mm,the most warm season precipitationis 118-691 mm,the coldest season precipitation is 4-97 mm,and the altitude may be between 500-2000 m.