Trilobite faunal successions across the Cambrian–Ordovician boundary intervals in Korea and their correlation with China and Australia

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The Cambrian–Ordovician boundary in Korea lies within the Choson Supergroup exposed in the Taebaeksan Basin and has been recognized in the Taebaek and Yongwol groups. The Taebaek and Yongwol groups show slightly different trilobite faunal successions across the putative Cambrian–Ordovician boundary intervals. In the Taebaek Group, saukiid-dominated, Missisquoia/ Onychopyge, and kainellid-dominated faunas occur successively in the basal part of the Tongjom Formation. While the remaining part of the Tongjom Formation is poorly fossiliferous, the succeeding Tumugol Formation yields fairly diverse trilobite faunal assemblages of late Tremadocian age. This implies that the Cambrian–Ordovician boundary in the Taebaek Group should be placed somewhere within the interval yielding the kainellid-dominated fauna. In the Yongwol Group, an uppermost Cambrian Fatocephalus fauna is more or less contemporaneous with the saukiid-dominated fauna of the Taebaek Group, while three Tremadocian trilobite faunas, i.e. Yosimuraspis, Kainella, and Shumardia zones in ascending order, are well represented in the Mungok Formation. The occurrence of Jujuyaspis in the Yosimuraspis Zone provides a firm basis for locating the Cambrian–Ordovician boundary at the base of the Mungok Formation. These Cambrian–Ordovician trilobite faunas of Korea are in general well correlated with those of China and Australia.