Reconstruction Of Paleovegetation And Paleoclimate Of The Late Miocene Flora In Tiantai, Zhejiang, China

The global climates in the Cenozoic had alternated frequently between the "greenhouse climate" and "icehouse climate". The studies of Cenozoic climatic changes are utmost important for the prediction of the future climate trends. Plant fossils as the first-hand materials in the life history of the earth almost have witnessed the whole geological courses and environmental changes in the Phanerozoic. Therefore, we can utilize fossil plants to reveal the climatic changes and environmental transitions in the past.The present plant fossils were collected from a diatomite layer of the Miocene Shengxian Formation in East Tiantai. Zhejiang Province. The fossils are mainly compressions which comprise of leaves, also include some fruits and seeds. In the present paper, the fossil elements from the Late Miocene Tiantai flora were classified based on the leaf architecture and cuticle features. The flora is composed of total 60 species which belong to 46 genera and 29 families. Thereinto, include 7 species of gymnosperms belong to 5 genera of 4 families,2 species of monocot angiosperms belong to 2 genera of 2 families, and the else are dicotyledons. The major members in the flora are Lauraceae, Leguminosae, Fagaceae and Ulmaceae, and the families such as Betulaceae, Hamamelidaceae, Aquifoliaceae, Smilaceae and Pinaceae also take up a partial percentage. The Tiantai Miocene plant assemblage displays a subtropical evergreen broad-leaved forest with some temperate trees. For example, the genera Cinnamomum, Litsea, Machilus, Castanopsis, Lithocarpus, Caesalpinia and Mallotus are generally distributed in the tropic or subtropic regions, but the genera Betula, Acer, Carpinus, Amelanchier, Cercidiphyllum and Cornus are the key elements in the northern hemisphere temperate forests.The present paper concluded that there was a lake with an altitude ca.300 m a.s.l. in the Miocene of East Tiantai. and the highest hills near the lake had the altitude about 1200 m a.s.l. The vertical vegetation distribution was also reconstructed. The hydrophyte Trapa lived in the lake:the evergreen broad-leaved forests and some single species forests of Cunninghamia and Pinus premassoniana distributed in the area of 300-600 m a.s.l., some shrub trees growing under the evergreen arbors, and the vines of Smilax climbing on the arbors or shrubs; the deciduous broadleaved forests with some evergreen trees distributed in the area of 600-1000 m a.s.l.; and the vegetations from 1000 m a.s.l. to 1200 m a.s.l. consisted of needle-defoliate broadleaved mixed forests.The paleoclimate of the Miocene Tiantai flora were reconstructed based on the coexistence approach (CA). overlapping distribution analysis (ODA). leaf margin analysis (LMA) and climate-leaf multivariate analysis program (CLAMP). The results show that the Late Miocene climate of East Tiantai was similar to that of today. Relative to the modern climate, the mean annual temperature (MAT) in the Late Miocene of Tiantai were nearly unchanged or slightly lower, the cold month mean temperature (CMMT) was similar to that of today, the warm month mean temperature (WMMT) was lower for 1-2.5℃, the difference in temperature between the coldest and warmest month (DT) was lower for 1-4℃, and the mean annual precipitation (MAP) was lesser for 176-272 mm.Combining the global climate change in the Cenozoic, the present paper compares the paleoclimates of the Late Miocene and the Early Pliocene of East Zhejiang and gives some conclusions for the changes of the Neogene paleoclimate and Asian monsoon system as follows. In the Late Miocene, the MAT, WMMT, CMMT and DT are close to those of today, which indicate that the Asian monsoon system had come into being in this period; after the Late Miocene, the monsoon was weakened and the global climate become hot, which resulted in higher MAT and CMMT in the Early Pliocene than those of Late Miocene and today, but the WMMT and DT in the Early Pliocene were very lower; since the Early Pliocene, the global temperature declined and the Asian monsoon was strengthened acutely, as a result that the modern monsoon system and climate were formed ultimately.