Facies of a Lower Ordovician carbonate shelf (Mungok Formation: Taebaeksan Basin,Korea) |
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Authors: | Dong Hee Kim Duck K Choi |
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Institution: | (1) School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, 151-742 Seoul, Korea |
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Abstract: | Summary The lithologic associations within the Lower Ordovician Mungok Formation in Korea define four depositional facies that formed
across a continental margin fringing the Sino-Korean block: these facies represent lagoonal/restricted marine, shoal, inner
shelf, and outer shelf environments. The stacking pattern of these facies reveals two systems tracts composed of five depositional
sequences. The lower highstand systems tract consists of the lagoonal/restricted marine and shoal facies, whereas the upper
lowstand systems tract comprises, in ascending order, inner shelf, outer shelf, and inner shelf facies. Three trilobite biofacies
are recognized in the Mungok Formation: i.e.,Yosimuraspis, Kainella, andShumardia biofacies in ascending order. TheYosimuraspis Biofacies is dominated byYosimuraspis but also containsJujuyaspis andElkanaspis. The predominance of the endemic eponymous taxon suggests a lagoonal/restricted marine environment. The nearly monotaxicKainella Biofacies, which comprises pandemic genera such asKainella and occasionallyLeiostegium, may represent a less restricted environment than theYosimuraspis Biofacies. TheShumardia Biofacies occurs in the marlstone/shale lithofacies through relatively thick stratigraphic interval and is dominated by cosmopolitan
trilobite taxa with some endemic species. The lithofacies and cosmopolitan trilobite assemblage of theShumardia Biofacies indicate that it occupied an outer shelf environment. The vertical succession of lithofacies and trilobite biofacies
in the Mungok Formation records in general a shift from a restricted, shallow water environment to deeper-water environment. |
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Keywords: | Lithologic associations Depositional facies Trilobite biofacies Taebaeksan Basin (Korea) Lower ordovician |
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