Darriwilian Radiolarians from Slope Facies Sediments, Ordos Basin, North China and Their Paleoecological and Paleogeographical Implications

A well-preserved Darriwilian radiolarian assemblage is reported from the Ordos Basin, North China. This new assemblage, recovered from the Kelimoli Formation in the Xilaifeng section, Wuhai area, Inner Mongolia, contains five species of five genera, including one new species. They are Proventocitum procerulum Nazarov, Oriundogutta bella Wang, Inanigutta complanata (Nazarov), Spongentactinia armillata (Nazarov), and Nyfrieslandia kelimoli sp. nov. The new species predominates this assemblage. Furthermore, the radiolarian assemblage from the lime mudstone of the Kelimoli Formation was associated with some other kinds of fossils including conodonts, brachiopods and acritarchs, which indicates a slope facies of the formation. The geographic distribution of Darriwilian radiolarian occurrences in Laurentia and peri-Gondwana region, based on available global data, highlights a preference of radiolarians for areas at low paleo-latitude. The results of quantitative biogeographic analyses, including Network Analysis (NA), Cluster Analysis (CA) and Non-metric Multidimensional Scaling (NMDS), indicate notable biogeographic provincialism of Darriwilian radiolarians in low-latitude areas (both in the southern and northern hemispheres). The southern hemisphere assemblages differ from those of the north in having higher taxonomic diversity that may have been associated with oceanic circulation.