Hakobuchi Formation
Geological formation in Hokkaido, Japan
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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]
Unit ofYezo Group
UnderliesIshikari Group, Poronai Group
OverliesHaborogawa Formation, Kashima Formation
| Hakobuchi Formation | |
|---|---|
| Stratigraphic range: Early | |
| 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 | |
| Location | 42.8°N 142.14°E |
| Region | East Asia |
| Country |  Japan |
| Extent | Hokkaido |
  Hakobuchi Formation (Japan) | |
Fossil content
Color key
|
Notes Uncertain or tentative taxa are in small text; |
Dinosaurs
Ornithopods
| Ornithopods of the Hakobuchi Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Kamuysaurus[5] | K. japonicus | A edmontosaurin saurolophine |  | |||
Mosasaurs
| Mosasaurs of the Hakobuchi Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Mosasaurus | M. hobetsuensis | A mosasaurine mosasaurid |  | |||
| Phosphorosaurus | P. ponpetelegans | A halisaurine mosasaurid |  | |||
Turtles
| Turtles of the Hakobuchi Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Mesodermochelys | M. undulatus | A dermochelyid turtle | .jpg) | |||
Fish
Cartilaginous Fish
| Cartilaginous Fish of the Hakobuchi Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Callorhinchus[6] | C. orientalis | A callorhinchid chimaeran |  | |||
Ray-finned Fish
| Cartilaginous Fish of the Hakobuchi Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Acipenseridae[7] | A sturgeon | |||||
Molluscs
Bivalves
| Bivalves of the Hakobuchi Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Inoceramus | I. nipponicus | A inoceramid bivalve | ||||
Cephalopods
| Cephalopods of the Hakobuchi Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Pachydiscus | P. japonicus | A pachydiscid ammonite |  | |||
Gastropods
| Gastropods of the Hakobuchi Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |