Abstract The Ordovician succession of the Korean Peninsula is part of the Cambro-Ordovician Joseon Supergroup exposed in the Taebaeksan Basin of South Korea and the Pyeongnam Basin of North Korea. This review summarizes the advances made on these successions over the past two decades, focusing on the Taebaeksan Basin. The Ordovician succession in the Taebaeksan Basin comprises the Taebaek, Yeongwol, Yongtan, Pyeongchang and Mungyeong groups, of which the Taebaek and Yeongwol groups have been studied in detail. These strata are mixed carbonate–siliciclastic deposits formed in peritidal to deep-subtidal environments. Sedimentological and palaeontological studies show that the Korean Ordovician succession represents local variations of the Great Ordovician Biodiversification Event, exemplified by reef evolution, changes in sedimentary systems and changes in invertebrate fossil assemblages. Recent studies of the Yongtan, Pyeongchang and Mungyeong groups have demonstrated that these units are important for understanding the tectonic evolution of the Taebaeksan Basin. The Ordovician strata in the Taebaek Group are generally similar to those of the Pyeongnam Basin and North China; however, the Upper Ordovician–Devonian strata between the two Korean basins show palaeontological affinities to those of South China, perhaps recording the Permo-Triassic collision between the Sino-Korean (North China) and South China blocks.

Abstract True hoppers, consisting of Fulgoromorpha and Cicadomorpha, are plant feeders with very high species-level diversity. A large number of true hopper fossils have been reported from eastern Asia, especially from the Middle to Late Jurassic Yanliao Biota, the Early Cretaceous Jehol Biota and mid-Cretaceous Kachin amber in the last two decades. Herein, true hoppers from the Jurassic and Cretaceous of eastern Asia are reviewed, and combining palaeontological data from other regions of the world and recent advances of molecular studies, the evolutionary history of true hoppers in the mid–late Mesozoic is discussed. Permocicada beipiaoensis Wang, 1987 and Archijassus plurinervis Zhang, 1985 are here excluded from Prosboloidea and Archijassidae, respectively. By the end of 2020, a total of 203 species with definite systematic position had been documented in the Jurassic and Cretaceous of eastern Asia (China, Myanmar, Siberia, Mongolia, Japan and Korea), and were attributed to 116 genera in 22 families and 7 superfamilies. Available fossil data suggest that true hopper components strongly changed in the Cretaceous: primitive groups reduced and went extinct successively, and the origin and/or early diversification of most lineages (family or subfamily level) occurred, likely owing to the displacement of host-plants in the angiosperm floristic revolution.

ABSTRACT The Gyeonggi Massif, Korea, consists of basement gneisses and supracrustal rocks migmatized to varying degrees. We conducted a petrologic-geochronologic study of the Mount Cheonggye gneisses, located in the western part of the Gyeonggi Massif, and we discuss the crustal evolution of the massif based on our results combined with a compilation of available data from the literature. Mineral assemblages and reaction textures in cordierite-garnet-biotite gneisses suggest a composite pressure-temperature path defined by two clockwise trajectories, M 1 and M 2 . Pseudosection modeling constrains M 1 peak metamorphic conditions as ~10.5 kbar and 840– 860 °C, followed by M 2 recrystallization at 4.5–5.5 kbar and 720–770 °C. Textural relationships of garnet to cordierite and kyanite to plagioclase transitions, as well as the pseudosection analysis, corroborate the clockwise pressure-temperature-time paths in the Gyeonggi Massif. We dated the polyphase metamorphism using sensitive high-resolution ion microprobe (SHRIMP) U-Pb data for zircon and monazite grains from eight samples. Overgrowth rims of zircon in a cordierite-garnet-biotite gneiss and a K-feldspar megacrystic orthogneiss yielded weighted mean 207 Pb/ 206 Pb ages of 1854 ± 9 Ma ( n = 11) and 1852 ± 12 Ma ( n = 19), respectively. This Paleoproterozoic age was reproduced by monazite grains from three cordierite-bearing gneisses dated at ca. 1861–1851 Ma. In contrast, monazite grains from a cordierite-bearing mylonitic gneiss and two biotite gneisses yielded consistent 206 Pb/ 238 U ages ranging from 235 ± 2 Ma ( n = 12) to 231 ± 2 Ma ( n = 15), suggesting a strong Triassic thermal overprint. Finally, we dated a postkinematic granitic dike at ca. 226 Ma, suggesting Late Triassic termination of the orogenesis. Our compilation of SHRIMP U-Pb ages from zircon, monazite, allanite, and titanite available from the literature confirms that the Gyeonggi Massif underwent two distinct thermal events in association with Paleoproterozoic (1.88–1.85 Ga) and Triassic (245–230 Ma) collisional orogenies. In contrast, Mesoproterozoic to Paleozoic thermal episodes are present in the Gyeonggi marginal belt, newly named in this study, where Neoproterozoic (ca. 950–750 Ma) and Paleozoic (ca. 450–430 Ma) ages are prominent in magmatic and detrital zircons. Our tectonic model, exemplified by the Qinling-Gyeonggi microcontinent, suggests that prolonged accretionary tectonics produced arc-related lithologies overlying the Gyeonggi Massif basement rocks. The juxtaposition of these terranes onto the Gyeonggi Massif produced tectonic mixtures with affinities to either the North or South China cratons. On the basis of similarities in zircon age distributions, we further suggest that the Qinling-Gyeonggi microcontinent is built upon basement rocks with North China craton affinity, at least in the Korean Peninsula and extending toward the Japanese Islands.