Occurrence of Changshania (Trilobita, Cambrian) in the Taebaeksan Basin, Korea and its stratigraphic and paleogeographic significance
In the Cambrian the Taebaeksan Basin was a shallow marine siliciclastic–carbonate system, in which two contrasting types of lithofacies and biofacies occur in juxtaposition. The shallow marine facies (Taebaek Group) comprises diverse trilobite taxa endemic to the Sino–Korean block, whereas the deep-water oceanic facies (Yeongwol Group) is characterized by predominance of cosmopolitan and pelagic trilobites. Changshania is a representative Furongian trilobite genus endemic to the Sino–Korean block and has been employed as a zonal taxon for middle Furongian in North China. This article reports the occurrence of Changshania from the deep-water facies (Machari Formation, Yeongwol Group) of the Taebaeksan Basin, for the first time in Korea. This observation enables to correlate the Eochuangia hana Zone of Korea with the Changshania–Irvingella Zone of North China with confidence. The dominance of laminated dark gray to black shale and pandemic trilobites in the Machari Formation has been interpreted to indicate deposition in a dysaerobic deep-water environment. The occurrence of Changshania along with some endemic polymerid trilobites, though uncommon, in the deeper-water oceanic facies suggests that the Machari Formation was formed in the offshore region fringing the Sino–Korean block during the Cambrian.