Yezo Group
The Yezo Group is a stratigraphic group in Hokkaido, Japan and Sakhalin, Russia which is primarily Late Cretaceous in age (Aptian to Earliest Paleocene). It is exposed as roughly North-South trending belt extending 1,500 kilometres through central Hokkaido from Urakawa to Cape Sōya and Sakhalin from the south coast to Alexandrovsk-Sakhalinsky District.[1] It consists of marine forearc basin sediments, typically turbiditic and bioturbated mudstones and sandstones with subordinate conglomerate primarily deposited on the continental shelf and slope of the ancient Yezo subduction margin. It forms a continuous depositional sequence with the Sorachi Group, which overlies the Horokanai Ophiolite. The sequence gradually shallows upwards with the terminal Hakobuchi Formation representing a fluvial-inner shelf environment.[2]
| Yezo Group Stratigraphic range: Aptian–Paleocene | |
|---|---|
| Type | Stratigraphic group |
| Sub-units | Hakobuchi Formation |
| Underlies | Ishikari Group, Poronai Group, Neogene deposits |
| Overlies | Sorachi Group |
| Thickness | 10,000 metres (32,810 ft) |
| Lithology | |
| Primary | Mudstone, sandstone |
| Other | Tuffite, conglomerate |
| Location | |
| Region | Hokkaido Sakhalin |
| Country |  Japan Russia |
Numerous fossils are known from the unit, mostly ammonites and bivalves, but also marine vertebrates such as mosasaurs and marine turtles. Dinosaur remains are among the fossils that have been recovered from the group, including those of an indeterminate maniraptoran consisting of a right metacarpal and manual unguals from the Early Campanian Osoushinai Formation from northern Hokkaido.[3] Nipponosaurus, which is known from an unnamed unit of the group from Southern Sakhalin probably late Santonian or early Campanian in age.[4] and Kamuysaurus, which is known from the early Maastrichtian Hakobuchi Formation of southern Hokkaido.[5]
See also
- List of dinosaur-bearing rock formations
References
- Shigeta, Yasunari; Maeda, Haruyoshi (2005). "Yezo Group Research in Sakhalin—A Historical Review" (PDF). The Cretaceous System in the Makarov Area, Southern Sakhalin, Russian Far East. National Science Museum Monographs. 31: 1–24.
- 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.
- Murakami, Mizuki; Hirayama, Ren; Hikida, Yoshinori; Hirano, Hiromichi (December 2008). "A theropod dinosaur (Saurischia: Maniraptora) from the Upper Cretaceous Yezo Group of Hokkaido, Northern Japan". Paleontological Research. 12 (4): 421–425. doi:10.2517/prpsj.12.421. ISSN 1342-8144. S2CID 128744799.
- Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, Asia)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 593-600. ISBN 0-520-24209-2.
- 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): 12389. Bibcode:2019NatSR...912389K. doi:10.1038/s41598-019-48607-1. PMC 6728324. PMID 31488887.