The Upper Ordovician Microfossil Assemblage From The Xilingxia Section In Quyuan Town,Zigui,Hubei

Extensive transgression events occurred during the Ordovician and the sea-level rise in the Late Ordovician was quite high.Marine creatures were developed and evolved rapidly during this period,especially Arthropods,Echinodermats,Mollusks,Vertebrates,etc.However,microfossils such as foraminifers,radiolarians and ostracods were rarely reported.Thus we collected loads of microfossils to do systematic palaeontology research in order to enrich the diversity of microbiota from the Upper Ordovician and discuss the contemporary sedimentary environment in the study area.The Upper Ordovician strata,including the Pagoda Formation,the Linhsiang Formation and the Wufeng Formation,from the Xilingxia Section in Zigui,Hubei Province yieded various and aboundant microfossils.After detailed identification,conodonts of 14 genus and 20 species(6 undetermind species),ostracods of 14 genus and 26 species(16 undetermined species)were recognized.Moreover,agglutinated foraminifers and spherical radiolarians were first reported from the Pagoda Formation and the Wufeng Formation in South China,namely Lagenammina sp.1,Lagenammina sp.2,Amphitremoida sp.,Armstrongisphaera sp.The conodont assemblage from the Pagoda Formation and the Linhsiang Formation was characterized by the HDS biofacies,which belong to relatively deep and cold water assemblage.The ostracod assemblage,dominated by Planoria,Fenxiangia,Schmidtella and Aparchites,could be compared with that from the Upper Ordovician Craighead Limestone Formation in southwest Scotland and the Esbataottine Formation in Canada,which indicate deeper marine environment.Spherical radiolarians from the Wufeng Formation,with low aboundance and diversity,were relatively well preserved and usually reported from the deeper water envieonment.Accordingly,the microfossils from the study area belong to deeper and colder water assemblage.The microfossils found in the Xilingxia Section constitute a deep-water biofacies of the Late Ordovician in the study area.In addition,foraminifers and radiolarians,first reported in South China,provide more paleontological data for the discussions of the early evolution of protist skeletons.According to the characteristic of microfossil assemblage as well as lithology,the Pagoda Formation and the Linhsiang Formation were considered as low energy and relatively deep shelf marine environment,the Wufeng Formation were thought as deep water environment.