Angiospermous Macrofossils From The Pliocene Of Yangyi,Western Yunnan And Their Biogeographical And Paleoenvironmental Significances

The plant macrosfossils from Yangyi coal mine?the Pliocene Yangyi Formation?in Baoshan,western Yunnan were studied detailedly on taxonomy.Eight angiospermous macrofossils are identified: Syzygium yangyiense Zhao sp.nov.,Cyclobalanopsis simoxyodon Zhao sp.nov.,Cyclobalanopsis sp.,Quercus cf.franchetii Skan.,Quercus cf.dolicholepis A.Camus.,Quercus cf.acrodonta Seem.,Castanopsis cf.delavayi Franch.,and Castanopsis cf.hystrix Miq..Using the global fossil records,the geohistorical distribution of Syzygium was discussed.Syzygium was mainly distributed in tropical zones of Asiain Cenozoic.Based on fossil records of Quercus,Cyclobalanopsis and Castanopsis,their origin time and migration history were documented.Quercus originated during the late Cretaceous to the late Paleocene.Cyclobalanopsis was originated before the early Eocene from eastern Asia.The origin time of Castanopsis was at least before the late Paleocene.They had migrated to high latitudes and reached to their distribution peaks in the Miocene.Then,the distribution of them reduced gradually and finaily formed the current distribution pattern.Based on the coexistence analysis?CA?of 16 macrosfossil species from the Yangyi coal mine,the paleoclimate of Yangyi during the late Pliocene was reconstructed quantitatively.The results show the annual mean temperature?MAT?of 13.3–19.2 ?,the mean temperature of the coldest month?CMT?of 3.3–10.7 ?,mean temperature of the warmest month?WMT?of 19.1–26.6 ?,and the mean annual precipitation?MAP?of 868–1307 mm,which are similar to those of today.The Stomatal Ratio of three Fagaceae fossil plants from the Pliocene Yangyi flora and their NLRs are utilized to reconstruct the paleoatmospheric CO₂ concentration.The paleoatmospheric CO₂ concentration during the Late Pliocene in Yangyi is range from 398 ppmv to 423 ppmv,which is similar to the present level.The survival altitude intervals of 16 NLRs of fossils were used to recover the paleoaltitude.Yangyi area had an altitude range from 1500 m to 2000 m a.s.l.during the late Pliocene.The current fossil site has an altitude of 1600 m a.s.l.,with a peak of 2300 m a.s.l.around the fossil site.Therefore,we infer that no prominent uplift had occurred since the late Pliocene in Yangyi area,western Yunnan.In addition,by comparing with other Neogene fossil floras,we speculated that the main uplift stages of the Hengduan Mountains might occurr between the Miocene and the late Pliocene.