Palynoflora From The Shengxian Formation Of Tiantai-Ninghai Area,Zhejiang,China And Its Palaeoenvironment And Palaeoclimate

The Shengxian Formation consists of the basalts of multiple stages with intercalations of sedimentary beds of fluvial-lacustrine facies, which formed under the tectonic background that a surge of volcanic activity had occurred in eastern China since the Cenozoic. These sedimentary beds are of great palaeoenvironmental and palaeoclimatic significance for a large amount of well-preserved fossil plants and sporopollen were found in them. Comprehensive and systematic studies have been carried out based on the macrofossil plants, including the depiction of the flora, studies on the morphology and anatomy of the taxa and the fossil plant based palaeoenvironmental and palaeoclimatic reconstruction. However, no matter on the pollen morphology or the palaeoenvironmental and palaeoclimatic reconstruction, only a few studies about the palynoflora from the Shengxian Formation had been conducted.11 samples were collected from the 3rd sedimentary layer of the Shengxian Formation in Tiantai-Ninghai area, Zhejiang Province of China. Through chemical treatment, except sample HNT-11, DLX-1 and DLX-2, abundant and well-preserved fossil spore-pollen was found in the rest of 8 samples. Most of the palynomorphs were referred to the natural classification at the genus or family level while the indeterminable taxa were designated to the morphotaxa. Totally,3333 pollen grains,559 algae were counted, then 39 palynomorphs were identified, including angiosperm taxa i.e., Pterocarya, Juglans, Carya, Corylus, Carpinus, Liquidambar, Quercus, Cyclobalanopsis, Fagus, Lithocarpus, Ulmus, Zelkova, Euphorbiaceae, Ilex, Ericaceae, Betula, Tiliaceae, Castanea, Rutaceae, Ebenaceae, Oleaceae, Celtis, Cyperaceae, Poaceae, Polygonaceae, Trapa’, Typha, Potamogetonaceae; gymnosperm taxa i.e., Podocarpaceae, Pinus, Keteleeria, Picea, Abies, Larix, Tsuga and T-C-T type (in this paper Taxodiaceae, Inaperturopollenites are included); fern taxa i.e., Polypodiaceae, Osmundaceae and an unknown affinity taxon Fupingopollenites.Then the palynological assemblage which is featured by Quercus-Pinus-Poaceae-Trapa was determined. The detailed morphological descriptions of the main taxa under the light microscope as well as the three-dimensional microstructures of some of the main taxa under the scanning electron microscope were acquired.By combining the macrofossil records from the same layer, the forest with a certain vertical zonality was recovered:with the elevation increasing, from the piedmont, evergreen broad-leaved forest with evergreen Quercus and Lauraceae as the main evergreen species, into a mixed evergreen and deciduous broad-leaved forest, further into a deciduous broad-leaved forest with Fagus, Carya, Carpinus, Liquidambar and Ulmus as the main deciduous species; there were also pine trees mixed in the broad-leaved forest and with herbs flourished and a certain amount of ferns grew there; bamboos were also inferred to grow in this area. Placid freshwater bodies were likely widespread in the area, for Trapa and Pediastrum as well as other aquatic herbs and freshwater algae flourished, which inferring that the precipitation would be high and the environment was humid. From the above, this type of vegetation is similar to the typical mid-subtropical evergreen broad-leaved forest concurrently with a certain vertical zonality which exists in Zhejiang Province nowadays. The palaeoclimatic parameters of the research area were obtained by applying the Coexistence Approach:mean annual temperature (MAT) from 17.0℃ to 18.5℃, mean temperature of the warmest month (WMT) from 26.5℃ to 28.4℃, mean temperature of the coldest month (CMT) from 3.3℃ to 7.7℃, difference in temperature between the coldest and warmest month (DT) from 18.2℃to 21.5℃, mean annual precipitation (MAP) from 979.0 mm to 1722.0 mm, mean maximum monthly precipitation (MMaP) from 176.2 mm to 265.0 mm, mean minimum monthly precipitation (MMiP) from 7.0 mm to 31.6 mm, mean precipitation of the warmest month (MWP) from 165.5 mm to 232.5 mm, indicating that in the Late Miocene, the climate in Tiantai-Ninghai area was warm and humid, similar to its modern climate.