Anatomic And Organic Geochemical Analysis Of Fossil Plants From The Late Miocene In Eastern Zhejiang Province, China

The Cenozoic is a very important era in which climatic and environmental dynamicsresemble modern ones, and angiosperms undergo intensely adaptive radiation. A Mioceneflora from the Xiananshan Formation of eastern Zhejiang Province, containing veryabundant compressive plant fossils, is a significant key for plant anatomy and organicgeochemical research. Now, anatomy and organic geochemistry are extremely usefulmethods and techniques for fossil taphonomy, molecular taphonomy and quantitativelypalaeoenvironmental reconstruction.Four predominant species in the Xiananshan Formation, including llex cornuta, Quercusdelavayi, Cunninghamia lanceolata and Liquidambar miosinica, are chosen from theMiocene Xiananshan Flora as materials of the current study. The molecular taphonomicdata and palaeoenvironmental information of the fossil flora are derived from theinvestigations on the four species by application of related taphonomic, anatomic,physiologic and organic geochemic techniques.Py-GC/MS results provide clues on organic molecular preservation status of the fourfossil species (from better to worse): L. miosinica≧C. lanceolata＞I.cornuta＞Q.delavayi. Variations of aliphatic compound observed on TIC among the four fossil species,and corresponding nearest living relative species (NLRs) as well as the deposits ofXiananshan Formation, show that aliphatic molecular preservation of the fossil remains isassigned to "in situ polymerization".As is well-known to all, a close negative correlation exists between atmospheric CO₂concentration and stomatal index of Quercus. Therefore, based on stomatal ratios andstomatal indexes of fossil and extant leaves of Q. delavayi, palaeoatmospheric CO₂ levels inthe late Miocene of Tiantai are estimated as 321 ppmv and 338 ppmv, respectively. Theresults are consistent with other relevant studies.85 morphotypes are identified from about 1000 angiosperm specimens of the XiananshanFlora. Consequently, the mean annual temperature (MAT) of 19.7～22.9℃in the LateMiocene Tiantai is derived from leaf margin analysis, the difference of temperatures ofcoldest and warmest mongth (DT) of 12.9～17.5℃is originated from a regressive correlation formula which is established between current MAT and DT. It indicates that theXiananshan flora belongs to a transitional type from subtropic to tropic vegetation.A close correlation is established between trichome base density of modern L. formosanaand climatic parameters. The trichome base density of fossil L. miosinica is ca. 10 (cm^-2),indicating that the late Miocene climate in Tiantai is similar to that in nowaday Guangzhou.Based on the empirical formula of Arens et al. (2000), atmospheric carbon isotopiccomposition (δ¹³C_atm)in the late Miocene is calculated from carbon isotopic composition(δ¹³C) of L. miosinica and is compared toδ¹³C_atm from carbonate isotope record, suggestingthat the species is not suitable forδ¹³C_atm estimates. And the result based on the fossil L.pachyphyllum from the Miocene Clarkia Formation in the U.S.A. agrees with the viewpoint.Carbon isotopic discrimination (Δ¹³C) of fossil Liquidambar is mainly related toenvironmental factors, such as irradiation, temperature, other than atmospheric CO₂concentration and water availability. According toΔ¹³C of fossil leaves, water useefficiency (WUE) is estimated to be 82μmolCO₂/molH₂O for L. miosinica,97μmolCO₂/molH₂O for L. pachyphyllum, respectively, and both the values are higher thantheir NLRs as well as WUE of sun morphotypes higher, which indicates that sunlight ortemperature is the significant impact on the WUE.