Cretaceous non-marine ostracod faunas of South Korea: Synthesis of taxonomy, biostratigraphy and paleoecology

This work presents the first review and comprehensive insights into ostracod faunas of the Cretaceous basins of South Korea. Based on previous literature and new data, a total of 57 species belonging to 13 genera, and nine ostracod assemblages are classified from 15 formations of six basins (Gyeongsang, Yeongdong, Hampyeong, Mokpo Volcanics, Haenam, and Sunchang basins). The ostracods of the Gyeongsang Basin can be divided into four assemblages in ascending order: Cyprideidae (Barremian–early Albian; Sindong Group), Cypridea–Ziziphocypris–Lycopterocypris (late Albian–Cenomanian; lower Hayang Group), Lycopterocypris–Cypria (Turonian–?Campanian; upper Hayang Group), and Mongolocypris (Campanian; Anpo Tuff). And, the ostracods from small basins are divided into five assemblages: Candona (Barremian–Aptian; lower strata of the Yeongdong Basin), Lycopterocypris (Aptian–Albian; Seonyudong Formation of the Yeongdong Basin), Mongolocypris–Cypridea–Candona (Aptian–?Cenomanian; Hampyeong Basin and Mokpo Volcanics), Cypridea–Candona (Campanian; Haenam Basin), and Mongolocypris–Cypridea (Campanian; Sunchang Basin). Most diverse taxa of the basins are the representatives of the superfamily Cypridoidea, especially the species of the genus Cypridea. These occurrences indicate the existence of numerous unstable lakes and temporary waterbodies. The pre-Aptian ostracod diversity is very low but peaked during the early Albian–Cenomanian. The species from the upper Albian-Campanian strata of the Gyeongsang Basin (especially Ziziphocypris and Lycopterocypris species) and the Aptian–?Cenomanian Hampyeong Basin exhibit significant similarities with ostracods from China and Mongolia, indicating active faunal exchanges and migration. The Cenomanian ostracods may represent a transitional fauna during the faunal turnover in East Asia, whereas ostracod diversity in the basins tends to decrease again during the Turonian–Campanian.