The Miocene Fagaceae From Eastern Zhejiang, China And Its Paleobiogeographical, Paleoenvironmental Significance

As the dominant component in tropical, subtropical, and temperate forests of the Northern Hemisphere, Fagaceae is widely distributed in Asia, Europe, North America, part of South America and the Pacific islands region. As such it is always one of the most important woody plants with numerous species and very widespread. Based on the geological history and fossil records, Fagaceae had a much wider distribution than at present at least in the Paleogene. With abundant fossil records, Fagaceae has been always the dominant component in the Northern Hemisphere since Neogene. Research on fossil Fagaceae could provide the evidence for the evolution and dissemination around the world of this family.The study area is located in the basinal-hilly areas of eastern Zhejiang Province, East China and adjacent to the East China Sea, where a mid-subtropical monsoon climate prevails. The stratum of study area, comprising many layers of basalt with intertrappean fluvial-lacustrine beds,is referred to as the Shengxian Formation. Basaltic dates and regional correlations indicate that the Shengxian Formation is confined to the upper Miocene. Many plant fossils are exquisitely preserved in this stratum, e.g., leaves, fruits and seeds as well as plentiful pollen.The statistics of this flora from the Shengxian Formation in eastern Zhejiang,shows that the Fagaceae is the dominant taxon. As a consequence,this dissertation will focus on the fossil leaves,cupules, and fruits belonging to the Fagaceae. Based on the morphological and anatomical analysis of a large number of extant Fagaceae and previous fossil records of this family,and using cladistics analysis, the present fossils are classified and identified as belonging to 5 genera of Fagaceae, with 15 species including 5 new species and 7 conformis or affinis to extant species.Using the morphology and anatomy of 57 extant species and 4 fossil species of Quercus subgenus Cyclobalanopsis, 22 characteristics are chosen for numerical taxonomy. The result shows that every fossil species is clustering on the nearest branch with its nearest living relative species,which is consistent with the identification results based on the morphological and anatomical analysis. The results of the Principal Component Analysis (PCA) show that,types of leaf shape,leaf margin, leaf teeth, lateral venation, trichome bases, accessory cell of stomata etc. are important morphological and anatomical characteristics of the 22 traits, contributing to the identification veracity of Fagaceae fossil.Time of origin, geohistorical distribution, paleobiogeographical significances of the 5 genera(Fagaceae) that exist in the late Miocene Shengxian flora are discussed in detail based on the fossil records in the world, combined with the theories of paleogeography and paleoclimate during the Cenozoic, uplift of the Tibetan Plateau, establishment of the monsoon system and formation of the arid area in Central Asia. The fossil records show that the Fagaceae originated in the Late Cretaceous, and the formation time of the present genera should be no later than the Paleocene.The oak genus with its abundant fossil records appears to have originated in the Paleocene. Since its origin Quercus differentiated into two subgenera, subg. Cyclobalanopsis and subg. Quercus.The former is limited to East Asia and Southeast Asia, while the latter is widespread in the temperate and subtropical regions of the Northern Hemisphere. The Cenozoic geohistorical distribution changes of Fagaceae indicate that the global climate is getting cold since the Miocene.Quercus is highly sensitive to environmental changes. The correlation between climate and trichome base density of Quercus glauca and Quercus delavayi of subg. Cyclobalanopsis, which are the NLRs of two fossil species, indicates that the trichome base density of Quercus glauca is comprehensively affected by variable climate factors, but most influenced by solar radiation and latitude. The trichome base parametrics of Quercus paraglauca and the comparison of epidermal cell characteristics between Quercus paraglauca and uercus aff.delavayi and their NLR species of subg. Cyclobalanopsis, show that the climate was warmer and more humid in the late Miocene than that of today in eastern Zhejiang, China. Studying on the stomata index of two extant species collected in different years, which are the NLRs of Quercus paraglauca and Quercus aff. delavayi,demonstrates that they are very sensitive to the variation of atmospheric CO2 concentration. By comparing the stomatal ratio between the two fossil species and their NLRs, the paleoatmospheric CO2 concentration in the late Miocene is reconstructed as ca. 400 ppmv, i.e. higher than the present natural CO2 concentration eliminating the industrial influence.