Study On Late Miocene Fabaceae And Elaeocarpaceae From Lincang,yunnan Province,China

Yunnan has a large number of exposed strata from the Cenozoic and is rich in plant fossils.It is one of the most important areas for studying the Cenozoic flora in China.The study area is located in the Bangmai Basin in Lincang,southwest Yunnan and south of the Hengduan Mountains on the southeastern edge of the Qinghai-Tibetan Plateau.The coal-bearing strata of the Miocene Bangmai Formation in the Bangmai Basin are well-developed and contain abundant plant fossils.Through the study of plant fossils collected from the Bangmai Formation,we can discuss issues such as the evolution of the local flora,the migration and diffusion process of species,and changes in the paleoenvironment.In this paper,we systematically classified and identified fruits and leaf fossils collected from the Bangmai Formation in Lincang,Yunnan.A total of 4 genera and 5species were identified: 1 new species and 1 known species of Sloanea,1 similar species of Sophora,1 new species of Zenia,and 1 new species of Bauhinia.Combined with the global fossil records of Sloanea,Sophora,Zenia,and Bauhinia with the distribution range of extant species,their paleobotanical geography was inferred: The early evolution center of Sloanea is in the central western region of North America,no later than the Paleocene.It spread to central Europe via the North Atlantic land bridge and then migrated from central Europe to southern Central Europe,Asia,and Oceania.By the Miocene,Sloanea had a geographic distribution pattern similar to that of modern times;Sophora may have originated in central western Japan or southwestern America before the early Eocene and discussed possible migration routes for Sophora from two origins;Zenia is an endemic genus in southern China.This paper is the first report of fossil records for this genus.It is speculated that its possible origin of center was southwestern China during the Oligocene to Miocene.After migration during geological history,it formed a geographic distribution pattern only in southern China and northern Vietnam;It is speculated that the early evolution center of Bauhinia is in western North America and should not be later than the Late Cretaceous.It spread to central western United States and northeastern China during the Paleocene.During Eocene-Oligocene period it spread to Western Europe,central Africa and Southeastern Asia.By the Miocene period its distribution range was similar to its present distribution.The migration route of Bauhinia shows a characteristic from high latitude to low latitude and from the northern hemisphere to southern hemisphere.This paper also reconstructs the paleoclimate and paleoaltitude of the Lincang area through the coexistence analysis method.From the reconstructed results: The annual precipitation in Lincang during the Late Miocene was 213.8 mm higher than nowdays;The mean temperature of coldest month was about 0.55℃ lower than nowdays;The average mean temperature of the warmest month was 2.28℃ higher than nowdays;The reconstructed paleoaltitude of Lincang was lower than the modern altitude(133～475 m lower),showing a climate characteristic with larger temperature difference,more abundant rainfall and more humid than nowdays.This is consistent with environmental changes caused by Lincang’s altitude rise since Late Miocene.Therefore,the overall paleoclimate in Lincang during Late Miocene was consistent with the current climate type in Lincang which is a subtropical monsoon climate.