Several Fossil Angiosperms From The Pliocene Of Tengchong,western Yunnan And Their Paleobiogeographic And Paleoenvironmental Significance

Tengchong county in west of Yunnan has complex topography and geological structure.It is also an important place for the preservation of Cenozoic plant fossils in China,which contains a large number of plant fossils.These plant fossils provide valuable research materials for the study of Cenozoic plants in the west of Yunnan.The study of Neogene fossils in west Yunnan can provide evidence for understanding the evolution and development of many plant groups in China and can extract the paleo-environmental information preserved in the fossils.And reconstruct the Neogene paleoclimate and its evolution in west Yunnan,providing reference for understanding the characteristics of Neogene climate in this area and studying the evolution and development of global climate.Based on the characteristics of leaf structure and cuticle microstructure,nine species of plant fossils are identified in Mangbang Formation of Tengchong,Yunnan Province.Syzygium Gaertn.:Syzygium tengchongense sp.nov.,Syzygium tuantianense sp.nov.,Syzygium mangbangense sp.nov.,Syzygium cf.buxifolium,Syzygium cf.tephrodes;Mahonia Nuttall:Mahonia mangbangensis sp.nov.,Mahonia cf.oiwakensis,Mahonia sp.;Buxus L.:Buxus cf.sinica.Based on the fossil records of the three genera,the paleobiogeography of the three genera is studied,and their origin,migration and evolution are discussed.The genus of Syzygium probably originated from east Gondwana paleocontinent.In the early Pliocene,western Yunnan became the origin and differentiation center of the new type of Syzugium.The Mahonia probably originated in western North America,migrated to Europe via the North Atlantic Land Bridge during the Late Eocene-Early Oligocene,and gradually spread to Asia during the Oligocene.The Buxus probably originated in Eurasia and migrated to The Americas via the Bering land Bridge during the Neogene.Based on stomatal parameters and?¹³C values,the stomatal ratio method and the photosynthetic gas exchange model method were used to reconstruct paleo-atmospheric CO₂concentration in the Late Pliocene of Tengchong county of western Yunnan.The mean value of palaeo-atmospheric CO₂ concentrations obtained by the stomatal ratio method was 417.9 ppmv,the mean value of 433.4 ppmv by the photosynthetic gas exchange modeling method.Two methods to reconstruct the results were similar,and similar to plant fossils stomatal ratio method is used for the reconstruction of the tengchong Paleo-atmospheric CO₂ concentration results,show that this reconstruction result has certain reliability.Both the stomatal ratio method and the photosynthetic gas exchange model method are suitable for the reconstruction of paleo-atmospheric CO₂.Based on the reconstructed results of paleo-atmospheric CO₂ concentration,the paleo-temperature range of the Late Pliocene in Tengchong county was 16.2-17.0?.Combined with the present distribution and living environment climate characteristics of Syzygium,Mahonia and Buxus,it is inferred that the late Pliocene in Tengchong was a warm and humid subtropical climate type,and the climate is not significantly different from today.