Fossil Lauraceae From The Late Pliocene Of Tengchong, Yunnan And Its Paleobiogeographical And Paleoenvironmental Significance

Modern Lauracea, a relative large phytogroup that wildly distributed in tropical, subtropical regions in Asia, America, Australia and Pacific islands, is a major component of the world’s tropical and subtropical forest as the most dominant taxa in the evergreen broad-leaf forest in these regions, but also very common in moist temperate forests. Lauraceae is relative ancient in angiosperm taxa. Research on fossil Lauraceae could provide the evidence of evolution and propagation of Lauraceae around the world. Yunnan Province, a wonderland with variety of vegetation types and abundant plant resource, is one of the best regions preserving the Cenozoic angiosperm fossils. This dissertation focuses on the Lauraceae fossils collected from upper member of the Mangbang Formation of Tuantian Town, Tengchong, Yunnan, which have significant implications for the analysis of climate and environment in the late Pliocene. Research on the Lauraceae of Tuantian flora in the late Pliocene in Tengchong, Yunnan, not only provides the first hand data on the evolution and distribution of Lauraceae plant in China, but also serves to extract data on paleoclimate and paleoenvironment, further providing paleobotanic evidence for the study on variation of climate and environment during the uplift of Tibetan Plateau.Abundant cuticles of extant Lauraceae are analysed for identifying the fossil specimens. Based on the high resolution photos taking under the light microscope and scanning electron microscope, the micro-features of cuticle are observed and described. Moreover, the combination of leaf architecture with cuticle microstructures improves the veracity of identification and classification of these Lauraceae fossils. The present fossils are classified and identified as totally 24 species, belong to 8 genera of Lauraceae by combining leaf architecture with cuticle microstructures. These fossil species include 1 new species,3 undefined species, and 16 conformis to extant species. The result suggests that the vegetation compositions of Tuantian flora in the late Pliocene have been very close to the modern one.Paleobiogeography significances of the 8 genera (Lauraceae) of the Tuantian flora in the late Pliocene are discussed based on the fossil records. The fossil records of Lindera, Cinnamomum and Litsea are more common, hence the paleogeographic evolution of these 3 genera is discussed in detail by combining plate drift, paleogeography and paleoclimate since the Cretaceous, uplift of the Tibetan Plateau, establishment of the monsoon system and forming of the aridity area in Centre Asia. Based on the fossil records of Cinnamonmum in the Miocene and the altitude of modern Cinnamomum distribution, the dissemination route of this genus was inferred and it is suggested that the altitude of the Tibetan Plateau did not exceed 2,500 m at that time.Comparing the relationship between drip-tip and precipitation of the nearest living relatives species (NLRs) of Lindera acuminatissima in Tuantian flora, the result shows that the length of the drip-tip of the species is correlated neither to the MAP (mean annual precipitation) nor to the MMMP (mean maximum monthly precipitation). Besides, the climate parameter of the distribution areas of the NLRs (Lindera tonkinensis) indicates that during the late Pliocene the MAT of Tuantian was not less than 17.5℃. Moreover, because of the influence of the Quaternary glacial epoch, the distribution of the Lindera acuminatissima was gradually confined to the lower latitudes.Relevance between climate and trichome bases of Cinnamomum camphora, which is the NLRs of the fossil species C. cf. camphora, indicates that the trichome density is comprehensively affected by climate factors. The result shows that the trichome density is more affected by solar radiation and annual precipitation, in the form of positively correlated with the intensity of solar radiation and negatively correlated with annual precipitation. The trichome base density of fossil is higher than that of the NLRs (C. camphora). It is probably affected by the intensity of solar radiation. It can be infered that during the late Pliocene the intensity of solar radiation in Tengchong was higher than that of today.Reconstructing the paleoatmospheric CO2 concentration of the geological time is an important part of paleobotanical and paleoenvironmental research. The NLRs of Lindera acuminatissima is L. tonkinensis. Studying of the relevance between stomata index of L. tonkinensis with climatic datum from different collection sites demonstrates that L. tonkinensis is a very sensitive species to the variation of atmospheric CO2 concentration, which was distributed in all of the 5 beds of the upper member of Mangbang Formation. By using the stomatal ratio of L. acuminatissima and L. tonkinensis, the paleoatmospheric CO2 concentration during 3.3-2.8 Ma is reconstructed, which fluctuated like the following:during 3.3-2.8 Ma is reconstructed, which fluctuated like the following:declined from 468ppm to 407ppm during 3.3Ma-3.1Ma, and increased from 407 to 506ppm during 3.13Ma-3.08Ma, declined again from 506ppm to 365ppm during 3.1Ma-3.0Ma, and declined more from 364.9ppm to 327ppm during 3.0Ma-2.8Ma. Overall, the paleoatmospheric CO2 concentration was a decline trending from 365ppm to 327ppm in 3.3-2.8Ma, but with fluctuations in each period.Comparing the venation characters of Lauraceae fossils from four fossil floras in the world, and that of extant Lauraceae in China, the result suggests that the proportion of Lauraceae species with ternate venation is on the rise. The proportion has rised from 10% in the Eocene to 12.5% in the late Pliocene in China, while that of modern one is 21%. Moreover, the proportion in Australia floras has rised from 8.3% to 10% from the Eocene to the Miocene. The results of leaf type classification statistics of Lindera acuminatissima indicate that, considering all the fossil leaves, type A is accounted for 24%, type B is 56% and typy C is 20% respectively. Comparing the above result to that of NLRs (L. tonkinensis), leaf type B is easier to be fossilized.