Depositional facies changes along the Yezo forearc basin transect and Cenomanian-Turonian oceanic anoxic event horizon: Yubari to Mikasa

寿男, 安藤; 憲一, 栗原; 賢一, 高橋

doi:10.5575/geosoc.113.s185

Cited by 3 publications

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“…Many previously reported tuff layers in various horizons of the Hakobuchi Formation (e.g., Ando, 1993;Ando et al, 2001Ando et al, , 2007) are undated. For example, undated tuff layers occur in the lower and uppermost parts of the Hakobuchi Formation in the Hobetsu area of Mukawa Town (e.g., Takahashi and Wada, 1987), where Kobayashi et al (2019) found a hadrosaurid Kamuysaurus japonicus.…”

Section: Implications Of the Present Studymentioning

confidence: 96%

“…Later, Okada et al (1998) showed that the section yielding S. triloculinoides is late Paleocene in age based on calcareous nannofossil biostratigraphy. In the Oyubari area, late Paleocene dinoflagellates (e.g., Alisocysta margarita) have also been reported in the Hakobuchi Formation (Suzuki et al, 1997;Ando et al, 2007). These marine fossils indicate that the Hakobuchi Formation extends geochronologically into the late Paleocene.…”

Section: Introductionmentioning

confidence: 97%

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

Kubomi,

Nagata,

Ota

et al. 2023

Jour. Geol. Soc. Japan

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The Hakobuchi Formation in Hokkaido, Northeast Japan, consists of marine and terrestrial clastic rocks of the uppermost part of the Yezo Group. The formation was previously interpreted to range from the early Campanian to the late Paleocene, with a hiatus near the K/Pg boundary. To date, no definitive evidence for the presence of the Lower Paleocene (Danian) has been identified in the formation. In this study, we present the LA-ICPMS zircon U-Pb dates of a tuff layer in the Hakobuchi Formation found in the Yubari area. Although the tuff contains Late Cretaceous to Paleocene zircon grains with 206 Pb/ 238 U concordant dates of 80.8-61.7 Ma, the weighted average age of the youngest date cluster was 64.1±1.1 Ma (2σ σ), suggesting that the depositional age of the tuff falls within the Danian. The results provide the first radiometric evidence indicating that the Hakobuchi Formation is at least partly correlated with the Danian, and are essential for discussing the depositional age of the Hakobuchi Formation and the geochronology of the Yezo Group.

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