PALYNOLOGICAL RECORDS OF THE COAL-BEARING DEPOSITION FROM THE MIDDLE JURASSIC IN YAOJIE,GANSU PROVINCE,NORTHWEST CHINA AND ITS PALAEOCLIMATIC SIGNIFICANCE
The Middle Jurassic Yaojie Formation is a typical coal-bearing sedimentary sequences in Northwest China. This our study conducted palynological analysis,shows that the palynoflora mainly consists of gymnosperms(Pseudopinus, Pinuspollenites,Pseudopicea,Protopicea and Podocarpidites)while pteridophytas chiefly represented by Cyatheaceae/Dicksoniaceae(Cyathidites/Deltoidospora)come next.There are still a small number of Osmundaceae (Osmundacidites),Taxodiaceae(Perinopollenites and Taxodiaceaepollenites)and Cheirolepidiaceae(Classopollis). The palynoflora as a whole indicates a relatively humid and warm climatic environment.From bottom to top,the components of the palynoflora showed significant changes,which can be roughly divided into three assemblages,Conifers- Ginkgophytes flora with bisaccates,tunicates and Chasmatosporites,Cyathidites/Deltoidospora-based Ferns flora and Conifers flora dominated by bisaccates and tunicates.Ferns and conifers reflect different climatic environment. Therefore,the possibility of a largeer climate changes are reflected by this vertical diversification of flora during the Middle Jurassic in the Yaojie area.