Re–Os Isotope Constraints on the Depositional Age and Regional Distribution of the Miocene Impact Ejecta Layer Around Minamitorishima Island, Western North Pacific

Extraterrestrial impact events have played an important role in global environmental changes and mass extinctions throughout the Earth’s history. Detecting traces of these events in oceanic settings is often difficult because of post-impact sedimentation. The marine Os isotopic composition serves as a valuable stratigraphic indicator and provides a powerful tool for detecting extraterrestrial material in marine sediments because of its high sensitivity to global environmental changes. Here, we report a new discovery of a clay layer with a high concentration of Os (613 ppt) and a conspicuous negative Os isotope anomaly (0.32), indicative of increased influx of extraterrestrial material, from a sediment piston core obtained southwest of Minamitorishima Island, western North Pacific Ocean. To estimate the depositional age of the ejecta layer, we applied the Limited-memory Broyden–Fletcher–Goldfarb–Shanno with Box constraints fitting algorithm using 187Os/188Os profiles. Our results yielded a depositional age of ca. 12 Ma, consistent with the previously discovered ejecta layer in another sediment piston core obtained south of Minamitorishima Island. Our results provide additional petrographic and geochemical evidence of an extraterrestrial impact during the Middle Miocene.