First discovery of the Kobayashi-Kasamori (Kb-Ks) tephra layer in terrestrial sediments of the Korean Peninsula

Abstract It was recently reported that a Quaternary basin in southeastern Korea was formed by a meteorite impact, and a 12-cm-thick tephra layer was found in lake sediments in this basin. In this study, we analyzed the geochemical composition and refractive index of glass shards to identify the unknown tephra. Based on both results, this tephra was identified as Kb-Ks tephra that erupted in the Kyushu area, Japan, approximately 520 ka. To our knowledge, this is the first report of Kb-Ks tephra in terrestrial sediments in the Korean Peninsula. These findings indicate that the depositional age of the lake sediments is much older than previously suspected (ca. 63 ka), and that the meteorite impact occurred before 520 ka. Although more detailed studies are needed, the discovery of Kb-Ks tephra provides important information concerning the paleoclimate during the middle Pleistocene, as well as the prediction of volcanic hazards in the Korean Peninsula.