Middle cambrian trilobites and biostratigraphy of the daegi formation (Taebaek Group) in the Seokgaejae section, Taebaeksan Basin, Korea

摘要

The Daegi Formation in the Taebaeksan Basin of Korea is composed of shallow marine carbonate facies and has been known to yield relatively diverse invertebrate fossils of middle Cambrian age. This paper describes seventeen trilobite species belonging to fifteen genera from the Daegi Formation exposed in the Seokgaejae section, located at southeastern corner of the Taebaeksan Basin. They comprise two agnostoid species(Ammagnostus laiwuensis andAmmagnostus sp.) and fifteen polymerid taxa (Dorypyge richthofeni, Amphoton deois, Blackwelderia sp.,Teinistion? sp.,Palaeadotes? sp.,Anomocarella temenus, ptychopariid gen. and sp. indeterminate.,Changqingia deprati, Crepicephalina damia, Cyclolorenzella rotundata, Cyclolorenzella sp.,Proasaphiscus sp.,Manchuriella macar, Ignotogregatus manholi, and Metanomocarella tumida). The stratigraphic distribution of these trilobites provides a basis for establishment of new trilobite zones within the formation: Le., theCrepicephalina, Amphoton, andCyclolorenzella zones in ascending order. TheCrepicephalina Zone is dominated byCrepicephalina damia, Manchuriella macar, Ignotogregatus sp. cf.I. manholi, andAmmagnostus laiwuensis. TheAmphoton Zone is recognized by the restricted occurrence ofAmphoton deois and dominance ofDorypyge richthofeni. TheCyclolorenzella Zone is characterized by the occurrence ofCyclolorenzella rotundata and some damesellid trilobites. These three biozones belong to middle to upper middle Cambrian in age and are closely correlated with theCrepicephalina, Amphoton, andDamesella-Yabeia zones of North China, respectively.