Hakobuchi Formation

{{Short description|Geological formation in Hokkaido, Japan}}

{{Infobox rockunit

| name = Hakobuchi Formation

| period = Maastrichtian

| age = Early {{fossilrange|Maastrichtian}}

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| type = Geological formation

| prilithology = Mudstone, Siltstone, Sandstone

| otherlithology = Tuffite

| unitof = Yezo Group

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| underlies = Ishikari Group, Poronai Group

| overlies = Haborogawa Formation, Kashima Formation

| thickness = Over {{Convert|450|m|ft|-1}}

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| region = East Asia

| country = {{flag|Japan}}

| extent = Hokkaido

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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.{{Cite journal|last=Takashima|first=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|hdl=2115/17182|hdl-access=free}} 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.{{Cite journal|last=Konishi|first=Takuya|last2=Caldwell|first2=Michael W.|last3=Nishimura|first3=Tomohiro|last4=Sakurai|first4=Kazuhiko|last5=Tanoue|first5=Kyo|date=2016-10-02|title=A new halisaurine mosasaur (Squamata: Halisaurinae) from Japan: the first record in the western Pacific realm and the first documented insights into binocular vision in mosasaurs|journal=Journal of Systematic Palaeontology|language=en|volume=14|issue=10|pages=809–839|doi=10.1080/14772019.2015.1113447|issn=1477-2019}} As well the sea turtle MesodermochelysHirayama R, Chitoku T. (1996). "Family Dermochelyidae (Superfamily Chelonioidea) from the Upper Cretaceous of North Japan". Transactions and proceedings of the Palaeontological Society of Japan. New series 184: 597-622. [http://translate.google.ca/translate?hl=en&sl=ja&u=http://ci.nii.ac.jp/naid/110002703433/&sa=X&oi=translate&resnum=6&ct=result&prev=/search%3Fq%3DMesodermochelys%26hl%3Den%26sa%3DG online, retrieved 28 July 2008] and the hadrosaurid dinosaur Kamuysaurus.{{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|pages=1–14|doi=10.1038/s41598-019-48607-1|pmid=31488887|doi-access=free|pmc=6728324}}