Study On Six Fagaceae Fossils From The Late Miocene Of Lincang,Yunnan Province And Reconstruction Of Paleoclimate

Since the Cenozoic,a series of great significant events have had a huge impact on the global geological structure pattern and climate changes.The uplift of Qinghai Tibet Plateau led to major changes of landforms and topography in Asia.It not only changed the climate pattern of Asia,which made the influence of the South Asia Monsoon gradually recede southward,and it is difficult to have a significant impact on the western part of China.As a result,China formed complex and diverse climatic types,which generally shows the pattern of drought in the West and humid in the East.Meanwhile,it also led to the evolution of palaeofloras of China since the Cenozoic.After the late Miocene,the global temperature gradually decreased and the Quaternary glaciation arrived as a result of the global tectonic movement and the change of atmospheric CO₂ concentration during the Cenozoic.Concurrently,due to the influence of the Himalayan movements,Yunnan formed a large number of small mountain basins.These small basins not only grow a variety of living plants,but also preserved lots of fossil plants.These fossil records have great significance not only for understanding of the evolution of paleofloras,but also for studying of the distribution pattern of extant plants.These fossils provide important material for the study of the plant diversity and its characteristics in the Cenozoic.The Bangmai basin of Lincang in Yunnan Province,as one of these small basins,preserved diverse plant fossils.The Bangmai paleoflora consisted mainly of fossil leaves,and totally comprises 37 families,59 genera and 71species.As one of dominant elements of this paleoflora,Fagaceae made up its constructive species.By study of Fagaceae fossils,we can not only enrich the plant fossil record of China since Cenozoic,but also reconstruct the paleoclimate during the geological past.In this investigation,on the basis of macroscopic and microscopic charact eristics of Fagaceae leaf fossils,they are identified and assigned into two genera,with six species,including one new species and two similar species.In addition,using cluster analysis,the Nearest Living Relative species(NLRs)of six fossil species were recognized.Meanwhile,based on the stomatal parameters and carbon isotopic values of the fossil species and their NLRs,four different models were used to quantitatively reconstruct the late Miocene paleoatmospheric CO₂ concenration.The results are399.0⁵05.4 ppmv by Stomatal Ratio Method,365.7³82.9 ppmv by Stomatal Index Method,368.3⁴09.6 ppmv by Photosynthetic Gas Exchange Model Method,and 305.5³67.7 ppmv by Plant Carbon Isotope Model method.Although the difference between the results of the four methods existed,the results are relatively close within the acceptable error range compared with the results from other global model reconstructions.In addition,through the comparison between different methods,the results obtained by Stomatal Ratio Method and Photosynthetic Gas Exchange Model was believed to be more accurate and close to the average value of other reconstructed results based on fossil plants,which could be representive of the late Miocene range of CO₂ concentration.According to carbon isotopic values of fossil and extant Quercus leaves,water-use efficiencies(WUE)of fossil and extant plants were calculated.The result indicates WUE of Quercus fossil plants was higher that of extant ones.It is believed that summer temperatures were mainly contributed to the difference in water-use efficiency of Quercus plants.