The Pliocene Tuantian Flora Of Tengchong, Yunnan Province And Its Paleoenvironmental Analysis

West Yunnan lies in the South of Hengduan Mountains and Southeast edge of theQinghai-Tibetan Plateau. It has been affected by the Himalayan tectonic movement sincethe Neogene, which has formed a complicated physiognomy, peculiar vegetation andtridimensional climate. The various vegetation conditions, abundant modern plantresources and plentiful Cenozoic fossil plants of West Yunnan can provide us goodmaterials for the studies of the plant diversity and paleoenvironmental evolvement. What isremarkable that the Neogene fossil plants from West Yunnan will greatly help us tounderstand the uplift and paleoclimatic evolvement of the Qinghai-Tibet Plateau.The combination of the leaf architectural and cuticular characters, will improve thereliability of the identification of fossil plants. Based on leaf architecture and cuticularanalysis, 1 gymnosperm species and total 36 angiosperm species which belong to 20families and 28 genera have been identified from the Pliocene Mangbang Formation ofTuantian Basin. The plant fossil assemblage shows that the Pliocene Tuantian flora ismainly composed of evergreen broad-leaved trees and living under a tropical or subtropicalclimatic condition.The evidences of anatomy and isotope geochemistry have proved that the leaf area,undulated degree of epidermal cell anticline, stomatal density and stomatal index, andδ¹³Cvalue can be regard as good indicators for the distinguish of sun and shade morphotypes offossil leaves. The cuticular and carbon isotope characters of fossil and modern leaves ofExbucklandia (Hamamelidaceae) show that the shade ecotype leaves usually possessbigger laminas, more undulated epidermal cell anticlines, and lower stomatal density,stomatal index andδ¹³C values. In addition, the present study also indicates that the sunleaves usually tend to be fossilized preferentially relative to the shade ecotypes.Reconstruct the paleoatmospheric CO₂ concentration of the geological history is animportance issue for palaeobotanical and paleoenvironmental research. In present study,the method of Stomatal Ratio on the 10 fossil plant species from the Pliocene Tuantianflora and their nearest living relatives are utilized to reconstruct the paleoatmospheric CO₂ concentration. The values of paleoatmospheric CO₂ concentration during the Late Pliocenein Tuantian Basin is range of 387.5-466.5 ppmv, and the mean value is 433.4 ppmv, whichis evidently higher than that of current levels.The paleoclimatic parameters were quantitatively reconstructed based on theCoexistence Approach of the NLRs of 37 fossil species from Tuantian flora. The resultsshow that the Pliocene paleoclimate of Tuantian Basin is characterized by the mean annualtemperature (MAT) 21.3-25.1℃, mean temperature of the warmest month (WMT)21.3-25.1℃, mean temperature of the coldest month (CMT) 10.8-14.6℃, difference intemperature between the coldest and warmest month (DT) 11.3-16.3℃, mean annualprecipitation (MAP) 1225.7-1638.3 mm, and relative humidity (RH) 75-82%. Thepaleoclimates of the Miocene Nanlin Formation of Tengchong, Miocene ShuangheFormation of Jianchuan and Pliocene Sanying Formation of Eryuan were as well asanalyzed by the Coexistence Approach. Comparing the paleoclimatic data of thesemacrofossil floras, the conclusion can be inferred that the areas of West Yunnan had notoccurred remarkable climatic changes from the Miocene to Late Pliocene, however, thetemperatures of Tengchong and Eryuan had declined quickly since the Late Pliocene.