Hakobuchi Formation

The Hakobuchi Formation is a geological formation in Hokkaido, Japan. It is the uppermost unit of the Yezo Group, being early Maastrichtian in age. It consists of bioturbated glauconitic sandstones, siltstones and conglomerates with coaly mudstone and minor tuffite. It was deposited in a continental shelf setting.^[1] It is noted for its fossil content with the invertebrates mainly consisting of bivalves and ammonites. With vertebrates including the mosasaurs Mosasaurus hobetsuensis and Phosphorosaurus ponpetelegans.^[2] As well the sea turtle Mesodermochelys^[3] and the hadrosaurid dinosaur Kamuysaurus.^[4]

Hakobuchi Formation
Stratigraphic range: Early Maastrichtian PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Yezo Group
Underlies	Ishikari Group, Poronai Group
Overlies	Haborogawa Formation, Kashima Formation
Thickness	Over 450 metres (1,480 ft)
Lithology
Primary	Mudstone, Siltstone, Sandstone
Other	Tuffite
Location
Region	East Asia
Country	Japan
Extent	Hokkaido

References

1. Takashima, Reishi; Kawabe, Fumihisa; Nishi, Hiroshi; Moriya, Kazuyoshi; Wani, Ryoji; Ando, Hisao (June 2004). "Geology and stratigraphy of forearc basin sediments in Hokkaido, Japan: Cretaceous environmental events on the north-west Pacific margin". Cretaceous Research. 25 (3): 365–390. doi:10.1016/j.cretres.2004.02.004. hdl:2115/17182.
2. Konishi, Takuya; Caldwell, Michael W.; Nishimura, Tomohiro; Sakurai, Kazuhiko; Tanoue, Kyo (2016-10-02). "A new halisaurine mosasaur (Squamata: Halisaurinae) from Japan: the first record in the western Pacific realm and the first documented insights into binocular vision in mosasaurs". Journal of Systematic Palaeontology. 14 (10): 809–839. doi:10.1080/14772019.2015.1113447. ISSN 1477-2019.
3. Hirayama R, Chitoku T. (1996). "Family Dermochelyidae (Superfamily Chelonioidea) from the Upper Cretaceous of North Japan". Transactions and proceedings of the Palaeontological Society of Japan. New series 184: 597-622. online, retrieved 28 July 2008
4. Sakurai, Kazuhiko; Sato, Tamaki; Chinzorig, Tsogtbaatar; Tanaka, Kohei; Fiorillo, Anthony R.; Chiba, Kentaro; Takasaki, Ryuji; Nishimura, Tomohiro; Kobayashi, Yoshitsugu (September 5, 2019). "A New Hadrosaurine (Dinosauria: Hadrosauridae) from the Marine Deposits of the Late Cretaceous Hakobuchi Formation, Yezo Group, Japan". Scientific Reports. 9 (1): 1–14. doi:10.1038/s41598-019-48607-1. PMC 6728324. PMID 31488887.