Palynoflora From The Guchengzi Formation Of The Fushun Basin And Its Paleoenvironment Implications

The Paleogene is an important geological period in the evolutionary history of the Cenozoic Earth.The global climate fluctuated significantly during this period.It is of great significance to study the paleoclimate of this period.In this paper,according to a detailed study of the palynoflora of the Early Eocene Guchengzi Formation in Fushun Basin,the paleovegetation and paleoclimate was reconstructed.The palaeoclimatic parameters of the research area were obtained by applying the Coexistence Approach.In this paper,43 samples collected from the Guchengzi Formation in the Donglutian Coal-Mine(East Open-Cut Coal-Mine)of the Fushun Basin were analyzed.Through chemical treatment,all samples contained a large amount of sporopollen fossils.According to the identification,there were 71 genera and 159 species of spores and pollen,among which the angiosperm pollen type was the most abundant,with 50 genera and 111species;followed by gymnosperm pollen,there were 14 genera and 35 species;fern spores contained the least type,with 7 genera and 13 species.Gymnosperm pollen are the highest in contents with overwhelming predominance of Taxodiaceaepollenites and Inaperturopollenites;the angiosperm pollen Ulmipollenites,Caryapollenites,Momipites and Quercoidites are abundant;while the fern spores,Polypodiaceaesporites and Osmundacidites have higher percentages in the composition.On the basis of the variations of main palynomorph taxa,three assemblages have been identified,i.e.Taxodiaceaepollenites-Momipites-Polypodiaceaesporites,Taxodiaceaepollenites-Ulmipollenites-Quercoidites,Taxodiaceaepollenites-Osmundacidites-Ulmipollenites-Pinuspollenites.Based on the analysis and identification of sporopollen fossils,Aquilapollenites spinulosus,Pistillipollenites macgregorii,and Tricolporopollenites hoshyamaensis with stratigraphic significance were found in the Guchengzi Formation.Combining with the previous data,it was further proved that the geological age of Guchengzi Formation isEarly Eocene.By comparing with the sporopollen assemblages of the same period strata in Northeast and North of China,it was found that there are some differences in the sporopollen assemblages between the Guchengzi Formation and the lower part of the Dalianhe Formation in Yilan area,Heilongjiang Province,the upper part of Huadian Formation in Huadian area,Jilin Province,the lower part of the Hunchun Formation in Hunchun area,Jilin Province,the Early Eocene strata in Wanchang area,Jilin Province and the Wutu Formation in Shandong Province.While the sporopollen assemblage of Guchenegzi Formation was highly similar with the second member of Kongdian Formation in Bohai Bay Basin,and it was inferred that the environment and climate of the two members were similar at that time.By assuming that the Paleogene plant taxa had similar climatic requirements to their nearest living relatives,the palynoflora revealed that the Early Eocene Fushun Basin was dominated by a mixture of evergreen and deciduous broad-leaved forest and the climate belonged to the subtropical warm and humid climate in nature.The palaeoclimatic parameters of the research area were obtained by applying the Coexistence Approach: mean annual temperature(MAT)was 14.9 ? ~15.8 ?,mean temperature of the warmest month(WMT)was 25.6?~27.5?,mean temperature of the coldest month(CMT)was 7.8?~11.4?,difference in temperature between the coldest and warmest month(DT)was 15 ? ~23.9 ?,mean annual precipitation(MAP)was 1011.3 mm~1 163 mm,mean maximum monthly precipitation(MMaP)was179.4mm~201.3 mm,mean minimum monthly precipitation(MMiP)was 11.3mm~ 21.5mm.Comparing the results with the current Fushun climate value,it was found that the mean annual temperature in the Early Eocene was 9.35? higher than the present,the mean temperature of the warmest month was 3.55 ? higher than the present,and the mean temperature of the coldest month was 24.3? higher than the present,the mean annual precipitation was 304.1 mm higher than the present.The Early Eocene climate of Fushun Basin is quite different from that in the present climate.According to the principle of climate classification,the Early Eocene in Fushun Basin is subtropical monsoon climate,and now it is temperate monsoon climate.