Delayed onset of the Great Ordovician Biodiversification Event: insights from Middle Ordovician carbonate succession in South Korea

초록

The Great Ordovician Biodiversification Event (GOBE) marks one of the most substantial evolutionary radiations in Earth's history. Its timing and regional expression, however, have largely been shaped by examples from relatively limited records and are still debated. To clarify these patterns, global-scale, integrative approaches are needed, especially in North China where they remain poorly understood. This study addresses this gap through a comprehensive paleoecological and sedimentological analysis of the Makgol and Duwibong formations in the Taebaeksan region of the Korean Peninsula, which constituted eastern North China during the Ordovician. Microfacies analysis of 1,543 samples identified 14 microfacies and demonstrated a significant increase in skeletal abundance. Skeletal abundance increased from < 1% in trilobite- and echinoderm-dominated assemblages of the Makgol Formation (lower Floian to lower Darriwilian), to approximately 17% in mollusk- and echinoderm-dominated assemblages of the Duwibong Formation (middle Darriwilian). This sharp increase is attributed to environmental changes following the middle Floian-lower Darriwilian hiatus, unfavorable to marine community development. Comparison with contemporaneous carbonate platforms in Laurentia, Baltoscandia, and South China highlights the diachronous nature and regional variability of the GOBE. These findings underscore the role of depositional contexts in shaping the regional onset and ecological characteristics of the GOBE.

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