New Progress on the Biostratigraphy of the Cambrian Kushan Formation (Guzhangian), North China

Based on the new investigation and new material collected from the twelve section from Shandong, Hebei and Liaoning Province, the lithostratigraphy and biostratigraphy of the Kushan Formation is revised. The lower boundary of the Kushan Formation is defined at the first appearance of grey, green-grey shale intercalated with grey, thin-bedded nodular limestone (Layer 93 in Jiulongshan section). The upper boundary of the Kushan Formation is placed on the light grey, thin-bedded edgewise limestone intercalated with grey shale, and base of the first appearance of the dark red to dark grey, thin-bedded glauconitic limestone (Layer 152 in Jiulongshan section) which characterizes the overlying Chaomitien Formation. Nine trilobite zones (including assemblage zones) are established for the Kushan Formation, which are (in ascending order): 1) Damesella paronai-Ajacicrepida ajax Assemblage Zone; 2) Damesella paronai-Teinistion typicalisAssemblage Zone; 3) Wongia (=Cyclolorenzella or Jiulongshania) rotundata Zone; 4) Wongia triangulataZone; ) Wongia subcylindrica Zone; 6) Wongia regularis Zone; 7) Neodrepanura-Liostracina tangwangzhaiensis Assemblage Zone; 8) Neodrepanura premesnili Zone; 9) Diceratocephalus armatus Zone. Additionally, a new assemblage zone, the Liostracina simesi-Placosema convexa Assemblage Zone, is established here for the basal Chaomitien Formation, which represents the uppermost trilobite zone of the Kushanian Stage (Guzhangian) in North China. This study also revised the taxonomic placement of nineteen species of trilobites Wongia, Cyclolorenzella, and Torifera, along with the establishment of three new species and two indefinate species: Wongia. nanzhaocunensis Yuan sp. nov., Wongia. laevigate Yaun sp. nov., Toriferaintermedia Yuan, Ren & Gao sp. nov., Cyclolorenzella sp., and Torifera sp., which delineated the ranges of the constituent species of Wongia, Cyclolorenzella, and Torifera between the Damesella paronai–Ajacicrepida ajax Zone of the uppermost Changhia Formation to the Diceratocephalus armatus Zone of the uppermost Kushan Formation. This study further subdivided the original genus–level biozones and established species–level biozones, facilitates the subdivision of pre-established fossil zones and the establishment of biozones based on the First Appearance Datum (FAD) of species, enabling the determination of the sequence of genera and species appearances in the stratigraphic record, significantly enhancing the precision of biostratigraphic correlation. A high–resolution biostratigraphic framework was established, it also contributes to the global correlation of the base of the Paibian Stage in North China.