The Late Cenozoic Floras From Eastern Zhejiang Province And Their Paleoclimatic Reconstruction

Zhejiang Province belonging to the middle-low latitudes of the Northern Hemisphere, is located in northern Southeast Hills, China and adjacent to East China Sea, where a mid-subtropical monsoon climate prevails. A continental stratum, comprising many layers of basalt with intertrappean fluvial-lacustrine beds, outcrops in the basinal-hilly areas of eastern Zhejiang Province, and is called lithologically the Shengxian Formation that is confined to the Miocene based on the geological constraints of the basaltic dates and regional correlations. Many plant fossils are exquisitely preserved in this stratum, e.g., fruits, seeds and leaves as well as very rarely discovered flowers. The present paper examined the morphological and anatomical characters of the macrofossils (mainly fruits and leaves) from the Late Miocene flora of the Shengxian Formation in Tiantai-Ninghai areas of Zhejiang Province, established detailed, valid systematic positions for the studied fossil plants; employed the present taxonomic results in combination with the previously published records of the other coeval and Late Quaternary fossil floras, qualitatively and quantitatively reconstructed the paleovegetation landscapes and the paleoclimates during the Miocene and Late Pleistocene-Early Holocene using the coexistence approach (CA) based on the nearest living relatives (NLRs) of the floral elements and the leaf margin analysis (LMA) based on fifty humid to mesic Chinese forests (Su et al.,2010), discussed the climatic change during the Late Cenozoic, eastern Zhejiang Province, and elucidated the age of the Neogene fossiliferous layers.The paper compared the morphological and anatomical characters of common fossil taxa from the flora with modern plants, assigned the common fossil plants to detailed, valid systematic positions:2 families 4 genera (at least 4 species) of conifers and 8 families 12 genera (at least 16 species, and 11 new species were described) of angiosperm, and recognized their living relatives; confirmed that the Miocene vegetation type is a notophyllous broad-leaved evergreen forest, and the paleofloristic type is both paleotropical-tertiary and arcto-tertiary; reconstructed that the Miocene vegetation landscape is a broad-leaved evergreen forest in the piedmont zone, a warm temperate/cool coniferous and broad-leaved deciduous forest as well as a bamboo forest in the higher hills or at the peaks; indicated that the Miocene forest has the vertical variation and a simple multistratified structure, which are similar to the modern subtropical broad-leaved evergreen forest distributed in Southeast China.The paper reconstructed the paleoclimate of the Miocene and Quaternary in eastern Zhejiang Province using the CA based on 58 NLRs of the fossil taxa from the Miocene Shengxian Formation and 46 NLRs of the fossil taxa from the Quaternary floras, respectively; and the Miocene climatic intervals are a MAT of 16.3-20℃, a WMT of 24.7-28℃, a CMT of 8.6-11.6℃, a DT of 15-17.4℃, a MAP of 1160.9-1653.5 mm, a MMaP of 175-300.4 mm and a MMiP of 15.5-36.5 mm, and the Quaternary climatic intervals are a MAT of 15-17.3℃, a WMT of 23.4-25.1℃, a CMT of 7.9-10.9℃, a DT of 15.3-21℃, a MAP of 1206-1921.2 mm, a MMaP of 196-332 mm and a MMiP of 31-64 mm. The calculated values are consistent with the temperature parameters of the corresponding forests of East Asia, and similar to the present climate in Zhejiang, while a decreasing CMT and an increasing DT from the Miocene to present indicate that the winter in eastern Zhejiang has been cooling and the monsoon has been strengthening, which coincide with the global Cenozoic climatic change and the origin and evolution of the modern East Asian monsoon.The paper used the Chinese equation established by the LMA based on fifty humid to mesic Chinese forests (Su et al.,2010), developed a MAT of 19.3±2.0℃in the Miocene, Zhejiang, which can overlap with the results of the CA. The corroborated climatic reconstruction estimated from the CA and LMA suggest that the present results are reliable and the Chinese equation is much more suitable for the climatic reconstruction of Chinese Cenozoic floras.The paper combined the publications of isotopic dates and regional stratigraphic correlation with those of plant fossil assemblages, and ascertained that the fossiliferous layer is confined to the Late Miocene Shengxian Formation using the chrono-, litho-and biostratigraphic techniques.