Yezo Group
{{distinguish|Yeso Group}}
{{Infobox rockunit
| name = Yezo Group
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| type = Stratigraphic group
| age = {{Fossilrange|Aptian|Paleocene}}
| period = Late Cretaceous
| prilithology = Mudstone, sandstone
| otherlithology = Tuffite, conglomerate
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| subunits = Shuparogawa Formation, Maruyama Formation, Hikagenosawa Formation, Saku Formation, Mikasa Formation, Kashima Formation, Haborogawa Formation, Osoushinai Formation, Hakobuchi Formation
| underlies = Ishikari Group, Poronai Group, Neogene deposits
| overlies = Sorachi Group
| thickness = {{Convert|10000|m|ft|-1}}
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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.{{Cite journal|last1=Shigeta|first1=Yasunari|last2=Maeda|first2=Haruyoshi|date=2005|title=Yezo Group Research in Sakhalin—A Historical Review|url=https://www.kahaku.go.jp/english/research/researcher/papers/18151.pdf|journal=The Cretaceous System in the Makarov Area, Southern Sakhalin, Russian Far East|publisher=National Science Museum Monographs|volume=31|pages=1–24}} 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.{{Cite journal|last1=Takashima|first1=Reishi|last2=Kawabe|first2=Fumihisa|last3=Nishi|first3=Hiroshi|last4=Moriya|first4=Kazuyoshi|last5=Wani|first5=Ryoji|last6=Ando|first6=Hisao|date=June 2004|title=Geology and stratigraphy of forearc basin sediments in Hokkaido, Japan: Cretaceous environmental events on the north-west Pacific margin|journal=Cretaceous Research|volume=25|issue=3|pages=365–390|doi=10.1016/j.cretres.2004.02.004|bibcode=2004CrRes..25..365T |hdl=2115/17182|hdl-access=free}}
Numerous fossils are known from the unit, mostly ammonites and bivalves, but also marine vertebrates such as mosasaurs, plesiosaurs{{Cite journal|last1=Kaim|first1=Andrzej|last2=Kobayashi|first2=Yoshitsugu|last3=Echizenya|first3=Hiroki|last4=Jenkins|first4=Robert G.|last5=Tanabe|first5=Kazushige|title=Chemosynthesis-Based Associations on Cretaceous Plesiosaurid Carcasses|url=https://www.academia.edu/1427886|journal=Acta Palaeontologica Polonica|year=2008 |volume=53|issue=1|pages=97–104|doi=10.4202/app.2008.0106 |s2cid=128406537 |issn=0567-7920|doi-access=free}} and marine turtles. Dinosaur remains are among the fossils that have been recovered from the group. These include a partial cervical vertebra and right hand from the therizinosaurid Paralitherizinosaurus, from Early Campanian Osoushinai Formation from northern Hokkaido.{{Cite journal |last1=Kobayashi |first1=Yoshitsugu |last2=Takasaki |first2=Ryuji |last3=Fiorillo |first3=Anthony R. |last4=Chinzorig |first4=Tsogtbaatar |last5=Hikida |first5=Yoshinori |date=2022-05-03 |title=New therizinosaurid dinosaur from the marine Osoushinai Formation (Upper Cretaceous, Japan) provides insight for function and evolution of therizinosaur claws |journal=Scientific Reports |language=en |volume=12 |issue=1 |pages=7207 |doi=10.1038/s41598-022-11063-5| pmid=35504901 |pmc=9065154 |bibcode=2022NatSR..12.7207K |issn=2045-2322}}{{Cite journal|last1=Murakami|first1=Mizuki|last2=Hirayama|first2=Ren|last3=Hikida|first3=Yoshinori|last4=Hirano|first4=Hiromichi|date=December 2008|title=A theropod dinosaur (Saurischia: Maniraptora) from the Upper Cretaceous Yezo Group of Hokkaido, Northern Japan|journal=Paleontological Research|volume=12|issue=4|pages=421–425|doi=10.2517/prpsj.12.421|s2cid=128744799|issn=1342-8144}} Nipponosaurus is known from an unnamed unit of the group from Southern Sakhalin, probably late Santonian or early Campanian in age.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}} Kamuysaurus, which is known from the early Maastrichtian Hakobuchi Formation of southern Hokkaido, was also discovered in layers of this group.{{Cite journal|last1=Sakurai|first1=Kazuhiko|last2=Sato|first2=Tamaki|last3=Chinzorig|first3=Tsogtbaatar|last4=Tanaka|first4=Kohei|last5=Fiorillo|first5=Anthony R.|last6=Chiba|first6=Kentaro|last7=Takasaki|first7=Ryuji|last8=Nishimura|first8=Tomohiro|last9=Kobayashi|first9=Yoshitsugu|date=September 5, 2019|title=A New Hadrosaurine (Dinosauria: Hadrosauridae) from the Marine Deposits of the Late Cretaceous Hakobuchi Formation, Yezo Group, Japan|journal=Scientific Reports|volume=9|issue=1|page=12389|doi=10.1038/s41598-019-48607-1|pmid=31488887|pmc=6728324|bibcode=2019NatSR...912389K|doi-access=free}}
Fossil content
=Reptiles=
=Fish=
=Echinoderms=
| class="wikitable" align="center" | ||||
| colspan="6" align="center" | Echinoderms reported from the Yezo Group | ||||
|---|---|---|---|---|
| Genus | Species | Presence
!Material | Notes | Images |
| ?Austinocrinus
|?A. sp. | Unknown locality, possibly in south-central Hokkaido, thought to be Santonian-Campanian.{{Cite journal |last=HUNTER |first=AARON W. |date=2012-12-12 |title=Crinoid diversity in the Upper Cretaceous Yezo Supergroup, Hokkaido, northern Japan |url=https://www.researchgate.net/publication/286342199 |journal=Zoosymposia |volume=7 |issue=1 |pages=71–80 |doi=10.11646/zoosymposia.7.1.7 |hdl=20.500.11937/60598 |issn=1178-9913}} |"One nodal and two pluricolumnals, associated on a bedding plane, so probably from a single individual". | A crinoid. | | ||||
| ?Balanocrinus
|?B. sp. |Upper Coniacian-Campanian portions of the Haborogawa Formation). |A crinoid. | | ||||
| Isocrinus
|I. sp. |Haborogawa Formation (upper Turonian-Coniacian). |A crinoid. | | ||||
| Isselicrinus
|I. sp. |Campanian upper Yezo Group. |One pluricolumnal and five very poorly preserved columnals. | | |
=Molluscs=
=Paleoflora=
See also
References
{{Reflist}}
{{coord missing|Hokkaidō Prefecture}}
Category:Geologic groups of Asia
Category:Geologic formations of Japan
Category:Geologic formations of Russia
Category:Lower Cretaceous Series of Asia
Category:Upper Cretaceous Series of Asia
Category:Cretaceous–Paleogene boundary
Category:Paleogene System of Asia