Chitinozoan biostratigraphy across the base of Darriwilian Stage from the type area in Eastern China

The base of the Darriwilian Stage is defined by the first appearance datum (FAD) of Undulograptus austrodentatus. The Darriwilian GSSP was formally designated in the Ningkuo Formation at the Huangnitang section, Zhejiang Province, eastern China. Four sections, i.e. Hengtang, Fengzu, Dianbatou and Chenjiawu sections, are systematically sampled for chitinozoan investigation. Abundant and diverse chitinozoans are recovered in the Ningkuo dark shales, and three distinctive assemblages (Assemblages A, B and C) are identified. Dramatic changes are documented between the third assemblage and the two preceding ones. The first appearances of Belonechitina zhejiangensis sp. nov., Lagenochitina praepirum sp. nov. and Sagenachitina sp. 1 are close to the base of the Darriwilian Stage. Thus, the association of B. zhejiangensis sp. nov., L. praepirum sp. nov. and Sagenachitina sp. 1 can be used as an auxiliary tool for locating the base of the Darriwilian Stage.Chitinozoan elements of the Laurentia and northern Gondwana realms coexist on the South China palaeoplate. This conforms that South China is a particularly suitable region for documenting biostratigraphic ties between the main Ordovician palaeoplates.Belonechitina zhejiangensis sp. nov., Belonechitina chenjiawuensis sp. nov., Bursachitina laminaris sp. nov., Lagenochitina praepirum sp. nov., Euconochitina hengtangensis sp. nov. regarded as new species are described and illustrated.