Stratigraphy and Fossil Diversity of the Early Cretaceous Jinju Formation

In this presentation, we introduce the Jinju Formation, a Lower Cretaceous sedimentary unit within the Gyeongsang Basin located in the southern part of the Korean Peninsula. This formation preserves a highly diverse fossil record, and the primary objective of this study is to assess the stratigraphic significance of these fossil assemblages. The Jinju Formation is tentatively dated to the Albian Stage of the Early Cretaceous. Its paleoenvironment is interpreted as a fluvio-lacustrine system, and its lithology is dominated by black to gray shale, interbedded with sandstone, mudstone, and carbonate rocks. The paleoclimate during the deposition of the Jinju Formation is inferred to have ranged from semi-arid to sub-humid conditions. Recent paleobotanical studies indicate that the lacustrine system served as a hydrological refugium under arid climatic episodes. The Jinju Formation yields a remarkably diverse fossil assemblage, including plants, trace fossils (vertebrate footprints), and exceptionally preserved invertebrates. Notably, its entomofauna is highly diverse, comprising 10 orders, 29 families, and 70 species. Several of these insect fossils exhibit taxonomic affinities with those from other localities outside the Korean Peninsula (e.g., China), despite discrepancies in their stratigraphic ages relative to the Jinju Formation. These inconsistencies highlight the need for further detailed stratigraphic and biochronological investigations to improve our understanding of the stratigraphy and paleoecosystem of East Asia during the Early Cretaceous.