Discovery of Early Paleocene (Danian) tuff from the Yezo Group in the Yubari area, Hokkaido, Northeast Japan

Kubomi, Ko*; Nagata, Mitsuhiro; Ota, Hiroto*; Miyata, Kazunori*; Oto, Shigeru*

Chishitsugaku Zasshi (Internet), 129(1), p.453 - 460, 2023/09

https://doi.org/10.5575/geosoc.2023.0011

The Hakobuchi Formation in Hokkaido, NE Japan, consists of marine to terrestrial clastic rocks of the uppermost part of the Yezo Group, was previously interpreted to range from Early Campanian to Late Paleocene age, with a hiatus near the K/Pg boundary. No definitive evidence of the depositional age indicating Lower Paleocene (Danian) has been reported from the formation so far. We reported the LA-ICPMS zircon U-Pb dates of a tuff layer of the Hakobuchi Formation in the Yubari area. The weighted average date of the youngest cluster was 64.1 1.1 Ma (2), suggesting the depositional age of the formation is Danian. The result is the first radiometric evidence indicating that the Hakobuchi Formation, at least partly, is correlated with the Danian, and is essential to discuss the depositional age of the Hakobuchi Formation and geochronology of the Yezo Group.