Fagaceae Fossils From The Pliocene Of Tengchong,Yunnan Province And Their Microstructure And Paleoenvironmental Analysis

Since the Cenozoic,the uplift of the Tibetan Plateau has significantly affected the topography,and geological structure of Yunnan,and formed its unique vegetation landscape and three-dimensional climate with obvious vertical zonation.Western Yunnan is one of the most important regions for the preservation of the Cenozoic fossils,there are many fossil floras in coal basins.These fossil floras produce various types of fossils,which provides materials for the study of the Cenozoic plants in western Yunnan.The fossil leaves of the Fagaceae from the Mangbang Formation were used as research materials,the paleoenvironment and paleoclimate were analyzed by means of Coexistence Approach method,Stomatal Index method and other methods.The research results provide important reference for understanding the evolution of the ecological environment in the study area since the Pliocene.Through the comparative study of leaf structure characteristics and the microscopic structure of cuticle,12 fossil species were identified,3 new species,8 similar species,1 indeterminate species.The paleoclimate data of the Pliocene in Tengchong area were quantitatively recovered by using the Coexistence Approach method,the MAT is 14.6-19.2?,CMT is 7.5-9.9?,WMT is 23.5?-23.7?,MAP is 1434-1496mm.This data is close to the climate of modern Tengchong area,and it is speculated that the climate was in a relatively warm and humid subtropical climate in the Pliocene.The CO₂ concentration of the Pliocene in Tengchong area was recovered by using the stomatal index of Castanopsis cf.kweichowensis,Castanopsis tengchongensis,Castanopsis praejucunda,Quercus cf.gilva,Quercus cf.lobbii,and the results showed that the atmospheric CO₂ concentration in the late Pliocene ranged from 322.66 to 518 ppmv,the average value was 443 ppmv,it indicates that CO₂ concentration in the Pliocene was slightly higher than today.In this paper,some Fagaceae fossils in the Mangbang Formation were selected for morphological characteristics measurement.By calculating leaf area and petiole width,the leaf mass per area?LMA?was recovered.The analysis results of the ecological balance strategy showed that,the Fagaceae plant in the late Pliocene was still dominated by intermediate species between“rapid return”and“slow return”,and there were also very few“slow return”type of species,which reflects in the Pliocene in Tengchong area plants grew in an environment of abundant precipitation and warm climate.Through the analysis of the Fagaceae fossil records form the Cenozoic in Yunnan,it was found that the Hengduan Mountains,which were rapidly uplifted in the Pliocene,caused the distribution of Castanopsis and Cyclobalanopsis retreat to the west and east side of the Hengduan Mountains,while the Quercus were less affected,there are still some Quercus remaining in the Hengduan Mountains.The uplift of the Hengduan Mountains formed the distribution pattern of the Fagaceae in the late Pliocene in Yunnan and it continues to this day.