Revision of the conodont zonation of the uppermost Hwajeol Formation (Furongian), Taebaeksan Basin, Korea

摘要

The uppermost interval of the Hwajeol Formation, Taebaeksan Basin, has been assigned to the Fryxellodontus inornatus-Monocostodus sevierensis-Semiacontiodus lavadamensis Zone. The main species in the zone are Fryxellodontus inornatus Miller, Hirsutodontus hirsutus Miller, Monocostodus sevierensis (Miller), Semiacontiodus lavadamensis (Miller), S. nogamii Miller, Utahconus utahensis (Miller), and Cordylodus proavus Muller. These species were re-examined to evaluate the biostratigraphy of the Bangteogol and Maesangol sections. Data were added from eleven sections around the Taebaeksan Basin, which were studied previously by the first author. Conodont occurrences above the Cambrooistodus minutus Zone are characterized by a lack of vertical and lateral continuity in sections. Conodont recovery is relatively poor but is sufficient for biostratigraphic assignment. This trend of conodont occurrence seems to be related to sedimentary process, including debris slides and eustatic sea-level fluctuation. Nevertheless, detailed study of the characteristic species of the zone leads to the conclusion that retention of the zone is reasonable. However, it is renamed the M. sevierensis-S. lavadamensis Zone because Fryellodontus inornatus occurs stratigraphically lower than the other two nominate species. The M. sevierensis-S. lavadamensis Zone is correlated with equivalent zones of western USA, Canada, North China, and Australia.