The Yezo Group is a

stratigraphic group In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into super ...

Hokkaido is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

and

Sakhalin Sakhalin ( rus, Сахали́н, r=Sakhalín, p=səxɐˈlʲin; ja, 樺太 ''Karafuto''; zh, c=, p=Kùyèdǎo, s=库页岛, t=庫頁島; Manchu: ᠰᠠᡥᠠᠯᡳᠶᠠᠨ, ''Sahaliyan''; Orok: Бугата на̄, ''Bugata nā''; Nivkh: ...

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

which is primarily

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

in age (

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

to Earliest

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

). It is exposed as roughly north–south trending belt extending 1,500 kilometres through central Hokkaido from Urakawa to

Cape Sōya is the northernmost point of the island of Hokkaidō, Japan. It is situated in Wakkanai, Sōya Subprefecture. The is at the cape, although the true northernmost point under Japanese control is a small deserted island called Bentenjima, northw ...

and Sakhalin from the south coast to Alexandrovsk-Sakhalinsky District. It consists of marine

forearc basin Forearc is a plate tectonic term referring to a region between an oceanic trench, also known as a subduction zone, and the associated volcanic arc. Forearc regions are present along a convergent margins and eponymously form 'in front of' the vol ...

sediments, typically turbiditic and bioturbated mudstones and sandstones with subordinate conglomerate primarily deposited on the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

and

slope In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...

of the ancient Yezo subduction margin. It forms a continuous depositional sequence with the Sorachi Group, which overlies the Horokanai

Ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found i ...

. The sequence gradually shallows upwards with the terminal Hakobuchi Formation representing a fluvial-inner shelf environment. Numerous fossils are known from the unit, mostly ammonites and bivalves, but also marine vertebrates such as mosasaurs, plesiosaurs and marine turtles. Dinosaur remains are among the fossils that have been recovered from the group. These include a partial

cervical vertebra In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sau ...

and right hand from the

therizinosaurid Therizinosauridae (meaning 'scythe lizards')Translated paper
is a family of derived (advanc ...

Paralitherizinosaurus ''Paralitherizinosaurus'' is an extinct genus of therizinosaurid dinosaur from the Late Cretaceous Osoushinai Formation of Hokkaido, Japan. The genus contains a single species, ''P. japonicus'', known from a partial right hand and cervical vertebr ...

'', from Early

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

Osoushinai Formation from northern Hokkaido. ''

Nipponosaurus ''Nipponosaurus'' (meaning "Japanese lizard") is a lambeosaurine hadrosaur from sediments of the Yezo Group, in Sinegorsk on the island of Sakhalin, which was part of Japan at the time of the species' classification. The type and only species ...

'' is known from an unnamed unit of the group from Southern Sakhalin, probably late

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. The ...

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. ''

Kamuysaurus ''Kamuysaurus'' is a genus of herbivorous edmontosaurin saurolophine hadrosaurid dinosaur from Late Cretaceous Maastrichtian marine deposits of the Yezo Group ( Hakobuchi Formation) in the Hobetsu area near the town of Mukawa, Hokkaido in Ja ...

'', which is known from the early

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

Hakobuchi Formation of southern

, was also discovered in layers of this group.

Fossil content

Paleofauna

Paleoflora

References

Geologic groups of Asia Geologic formations of Japan Geologic formations of Russia Lower Cretaceous Series of Asia Aptian Stage Albian Stage Upper Cretaceous Series of Asia Cenomanian Stage Turonian Stage Coniacian Stage Santonian Stage Campanian Stage Maastrichtian Stage Cretaceous–Paleogene boundary Paleogene System of Asia Danian Stage Mudstone formations Sandstone formations Tuff formations Conglomerate formations Paleontology in Japan Paleontology in Russia {{hokkaido-geo-stub

Fossil content

Paleofauna

Paleoflora

See also

References