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 superg ...
in
Hokkaido
is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...
,
Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
and
Sakhalin
Sakhalin ( rus, Сахали́н, p=səxɐˈlʲin) is an island in Northeast Asia. Its north coast lies off the southeastern coast of Khabarovsk Krai in Russia, while its southern tip lies north of the Japanese island of Hokkaido. An islan ...
,
Russia
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
which is primarily
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...
in age (
Aptian
The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...
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), ...
). It is exposed as roughly north–south trending belt extending 1,500 kilometres through central Hokkaido from
Urakawa
is a List of towns in Japan, town located in Hidaka Subprefecture, Hokkaido, Japan. As of 1 October 2020, the town has an estimated population of 12,074 and a population density, density of 17 persons per km2. The total area is 694.24 km2.
...
to
Cape Sōya
is the northernmost point of the island of Hokkaidō, Japan. It is situated in Wakkanai, Hokkaido, Wakkanai, Sōya Subprefecture. The is at the cape, although the true List of extreme points of Japan, northernmost point under Japanese control ...
and Sakhalin from the south coast to
Alexandrovsk-Sakhalinsky District
Alexandrovsk-Sakhalinsky District () is an administrative district (raion) of Sakhalin Oblast, Russia, one of the seventeen in the oblast.Law #25-ZO As a municipal division, it is incorporated as Alexandrovsk-Sakhalinsky Urban Okrug.Law #524 It i ...
. It consists of marine
forearc basin
A forearc is a region in a subduction zone between an oceanic trench and the associated volcanic arc. Forearc regions are present along convergent margins and eponymously form 'in front of' the volcanic arcs that are characteristic of convergent ...
sediments, typically
turbiditic
A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in the process. ...
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 islan ...
and
slope
In mathematics, the slope or gradient of a Line (mathematics), line is a number that describes the direction (geometry), direction of the line on a plane (geometry), plane. Often denoted by the letter ''m'', slope is calculated as the ratio of t ...
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 (Earth), upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks.
The Greek word ὄφις, ''ophis'' (''snake'') is ...
. 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 (: 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 sauropsid s ...
and right hand from the
''
Paralitherizinosaurus
''Paralitherizinosaurus'' is an extinct genus of therizinosaurid theropod dinosaurs from the Late Cretaceous Osoushinai Formation of Hokkaido, Japan. The genus contains a single species, ''Paralitherizinosaurus japonicus'', known from a partial ...
'', 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. Campa ...
Osoushinai Formation from northern Hokkaido.
''
Nipponosaurus
''Nipponosaurus'' (meaning "Japanese lizard") is a Lambeosaurinae, 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 sp ...
'' 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 m ...
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'', which is known from the early
Maastrichtian
The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...
Hakobuchi Formation of southern
Hokkaido
is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...
, was also discovered in layers of this group.
Fossil content
Reptiles
Fish
Echinoderms
Molluscs
Paleoflora
See also
*
List of dinosaur-bearing rock formations
This list of dinosaur-bearing rock formations is a list of geologic formations in which dinosaur fossils have been documented.
* List of stratigraphic units with dinosaur body fossils
* List of stratigraphic units with dinosaur trace fossils
** ...
References
{{coord missing, Hokkaidō Prefecture
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 groups
Sandstone groups
Tuff groups
Conglomerate groups
Paleontology in Japan
Paleontology in Russia