New Discovery Of Early Cretaceous Fossil Plants And Palynoflora From Binggou Area,Jianchang County,Liaoning Province

Jianchang Basin is one of the important Mesozoic continental sedimentary basins of the western Liaoning province.It is located in the northeast part of North China plate and the east section of Yanshan tectonic belt.The Early Cretaceous Binggou Formation is well developed in this basin with abundant coal resources,but the fossil plants and palynoflora from those strata had never been well studied.In this thesis,detailed taxonomic research of plant megafossils and sporopollen fossils from the Binggou Formation is presented for the first time.Based on the flora composition,we inferred the geological age of Binggou Formation,and reconstructed the paleoclimate and palaeoecology of Early Cretacous Binggou region.The research provides significant information for studying the paleoclimate,palaeoecosystem and paleogeographic division of the Early Cretaceous Northeastern China.All the megafossils and sporopollen described here were collected from the middle and lower part of Binggou Formation,which are consist of detrital sandstone,shale and siltstone with coal seam.21 species of 16 genera were identified,including Sphenopsida,Filicopsida,Cycadopsida,Ginkgopsida,Czekanowskiales,Coniferopsida,and fructus et semina.Two new species,Pterophyllum binggouensis sp.nov.and Pityophyllum binggouensis sp.nov.are established.Pityophyllum binggouensis sp.nov.is the first report of fossil genus Pityophyllum with well –preserved cuticle,that updates the knowledge of classification and evolution of Pinaceae.The Binggou palynoflora is composed by 134 species of 49 genera.Amongthem,the pollen of gymnosperms dominates(53.3%–60.8%),followed by spores of pteridophytes(39.2 – 46.6%).Disaccate pollen takes the highest proportion in gymnosperm while the Lygodiaceae spore is the richest in pteridophytes.Also,the composition is lack of Pilosisporites and Classopollis.These characters present a typical Early Cretaceous palynoflora in the northeastern China.According to different sporopollen species and sporopollen composition percentage in this palynoflora,two palynological assemblages are recognized in ascending order.The assemblage ? is Cicatricosisporites–Osmundacidites–Piceites assemblage,other elements,such as Concentrisporites,Pinuspollenites,Podocarpidites et al.are occurred.The assemblage ? is Cicatricosisporites–Osmundacidites–Erlianpollis assemblage,accompanied with Pinuspollenites,Piceaepollenites,Abietineaepollenites et al.The two assemblages could be correlated to the assemblages of Shahai Formation and Fuxin Formation.Combined with the major elements of the current assemblages,the geological time of Binggou Formation can be limited between Barremian and Aptian of Early Cretaceous.The Early Cretaceous Binggou megafossils assemblage is rich in conifers,associated with ferns,ginkgoaleans and cycadaleans,which indicates a warm –temperate to medium–temperate climate with seasonal variation.The composition and the representative plans of this assemblage represent a typical northern flora of the Early Cretaceous in Eurasia.The sporopollen assemblage is abundant in Binggou Formation.Among them,most of the members are forestation gymnosperm plants or ferns.The feature of sporopollen assemblage also indicates a warm and humid climate condition with a seasonal variation.In conclusion,Binggou flora is similar to that in the south margin of Early Cretaceous Siberia–Canada Floristic Region.This Region was covered with forest vegetation in Early Cretaceous and represented a warm and humid climate condition with seasonal variation.Notably,the two assemblages of palynoflora show a vegetation changing from the lower to upper part of Binggou Formation,as the pteridophytes increasing and gymnosperms decreasing.The change reflected that,during this period,the climate may get warmer and more humid,which has responded to the global climate change during Barremian–Aptian.