Biostratigraphy Of Fuxin And Sunjiawan Formations And Upper-lower Cretaceous Boundary In Western Liaoning - Eastern Inner Mongolia, China

As a classic research area of early Cretaceous,western Liaoning-eastern Inner Mongolia forms the lower unit of Cretaceous non-marine sequence in northern China.The non-marine deposits of Early Cretaceous are well-developed and the identification of its stratigraphic sequence is of great significance to the establishment of non-marine Cretaceous stratigraphic system.This research focuses on the strata units near the Lower and Upper Cretaceous boundary in western Liaoning-eastern Inner Mongolia.Based on extensive fieldwork and systematic analysis,the attribution of “Banlashan Formation” has been discussed further.Most of samples were collected from the middle-upper section of Fuxin Formation.36 pteridophyte spores and 22 gymnosperm pollen grains were recorded and no angiosperm pollen grains were found in this research.4 palynomorph assemblages have been set up in the middle-upper section of Fuxin Formation and their characteristics are respectively recorded in details from bottom to top:Cyathidites-Cicatricosisporites-Pinuspollenites assemblage from the upper part of Zhongjian section,Deltoidospora-Appendicisporites-Concentrisporites assemblage from Sunjiawan section,Deltoidospora-Cicatricosisporites-Classopollis assemblage from the lower part of Shuiquan section,and Deltoidospora-Cicatricosisporites-Appendicisporites assemblage from the upper part of Shuiquan section.The palynofloras in the lower section of Fuxin Formation are similar to those from Yingcheng Formation while the palynofloras in the upper section are similar to those from Denglouku Formation in Songliao Basin but bear their own unique features at the same time.Fuxin Formation correlates to later Aptian-Albian stage combining the isotopic data.In addition,two charophytes are first discovered in Fuxin Formation: Mesochara cf.voluta(Peck)Grambast and Aclistochara mundula Peck,which are common in Cretaceous.Based on the data of microfossils,biostratigraphy,isotope stratigraphy,sedimentary evolution stages,climate change,and the sedimentary background of Sunjiawan Formation has been further discussed.It is proposed that Sunjiawan Formation corresponds toCenomanian stage in Upper Cretaceous and can be correlated to Quantou Formation in Songliao Basin and the Lower/Upper Cretaceous boundary in western Liaoning-eastern Inner Mongolia is located in the bottom interface of Sunjiawan Formation.