MAJIMA Ryuichi


Faculty of Environment and Information Sciences, Division of Natural Environment and Information

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The Best Research Achievement in Research Career 【 display / non-display

Graduating School 【 display / non-display


    Yokohama National University   Faculty of Education   Graduated

Graduate School 【 display / non-display


    University of Tsukuba  Graduate School, Division of Earth Science  Geology    Completed

Degree 【 display / non-display

  • Doctor of Science -  University of Tsukuba

Campus Career 【 display / non-display

  • 2011.04

    Duty   Yokohama National UniversityFaculty of Environment and Information Sciences   Division of Natural Environment and Information   Professor  

  • 2001.04

    Duty   Yokohama National UniversityCollege of Education and Human Sciences   Professor  

  • 1997.10

    Duty   Yokohama National UniversityCollege of Education and Human Sciences   Associate Professor  

  • 1995.04

    Duty   Yokohama National UniversityCollege of Education   Associate Professor  

  • 1991.04

    Duty   Yokohama National UniversityCollege of Education   Research Associate  

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Field of expertise (Grants-in-aid for Scientific Research classification) 【 display / non-display

  • Stratigraphy/Paleontology

  • Taxonomy

  • Geology

  • Paleontology


Research Career 【 display / non-display

  • Chemosynthetic fossil assemblage

    Grant-in-Aid for Scientific Research  

    Project Year:  -   

  • Taxonomic study of the Kakegawa-type fauna.

    Project Year:  -   

  • Taphonomy of molluscan fossils

    Project Year:  -   

Books 【 display / non-display

  • Introduction of Paleontology

    Majima, Ryuichi and Ikeya, Noriyuki (Part: Joint Work )

    Asakura Publishing Co.,Ltd.  1996.01 ISBN: 978-4254162745

Thesis for a degree 【 display / non-display

  • Paleontological study of the Cenozoic Naticidae in Japan.

    Majima, Ryuichi 


    Doctoral Thesis   Single Work

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Papers 【 display / non-display

  • Cold-seep-dependent fossil assemblages in the middle Pleistocene Kakinokidai Formation at Kawayatsu, Kimitsu City, Japan: Their temporal–spatial distribution and associated authigenic carbonates

    Ryuichi Majima, Mayumi Ochi, Misa Miura, Makiko Hitomi, Takeshi Saito, Yuki Namiki, Yusuke Ohtsuka, … Show more authors

    Journal of the Geological Society of Japan ( Geological Society of Japan )    2019  [Refereed]

    Joint Work

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    Cold-seep-dependent molluscan assemblages occur in the outer shelf facies of the middle Pleistocene Kakinokidai Formation of the Kazusa Group, a forearc basin-fill sequence on the Pacific side of central Japan, in strata corresponding to the interval 707.6–667.0 ka. The assemblages consist exclusively of chemosymbiotic bivalves (lucinids, thyasirids, and solemyids) and are associated with 13C-depleted authigenic carbonates (δ13C: −61.60 ‰ to −10.96 ‰ VPDB), which suggest that their main carbon source was the anaerobic oxidation of methane (AOM). Authigenic carbonate precipitates are common on burrow walls (mainly acicular aragonite) and the surrounding sediments (mainly micritic high-Mg calcite and dolomite). The burrows are cylindrical, 1.5–3.0 cm in diameter, and over 1 m long. Callianassid claws and the trace fossil Palaxius (probable callianassid fecal pellets) in the burrow carbonates suggest that the burrows were produced by sediment-dwelling callianassid decapods. We propose the following formation mechanism of burrow and its related authigenic carbonates. Firstly, callianassids produced deep burrows, penetrating the AOM zone and reaching the methonogenic zone. Methane then seeped into the burrows and AOM occurred in its deeper parts, promoted by a supply of seawater via callianassid activity, resulting in an increase in the concentration of hydrogen sulfide ions. Thiobacteria flourished in the shallower parts of the burrows, which were enriched in dissolved oxygen, and provided a source of food for the callianassids. In the deeper parts of the burrows, acicular aragonite precipitated around suspended carbonate nuclei and sank to the bottoms of the burrows, forming geopetal-like carbonate structures. In the surrounding sediment, high-Mg calcite precipitated in response to an increase in the concentration of phosphate ions (due to the decomposition of organic matter) and dolomite precipitated in response to decreasing concentrations of sulfate ions, caused by active AOM.

  • Chemosynthetic, cold-seep-dependent fossil assemblages from the upper part of the Nakatsu Group (Lower Pleistocene), Sagamihara City, Kanagawa Prefecture, central Japan

    Hiroki Seto, Ryuichi Majima, Shoichi Miroku and Eiko Nakamura

    fossils ( Palaeontological Society of Japan )    2019  [Refereed]

    Joint Work

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    Chemosynthetic, cold-seep-dependent fossil assemblages occur at five fossil localities in the riverside cliffs along the Sagami River, Sagamihara City, central Japan, where the upper part (2.5–2.0 Ma) of the marine Nakatsu Group is exposed. The upper Nakatsu Group is marked by coarsening-upward and subsequent fining-upward sequences as follows (in ascending order): mudstone (Lithofacies A), mudstone and sandy mudstone (B), sandy mudstone (C), alternations of sandy mudstone and muddy sandstone (D), sandy mudstone (E), and mudstone (F). The fossil assemblages are dominated by the bivalve molluscs Lucinoma and/or Conchocele that show high rates (79.2%–100%) of valve articulation, occur in clusters, and are frequently preserved in life positions. The fossils are commonly associated with authigenic carbonate concretions consisting of high-magnesian calcite and/or dolomite that are greatly depleted in 13C (δ13C = −33.31‰ to −22.60‰ VPDB), suggesting the influence of anaerobic oxidation of methane. These observations indicate that the fossil assemblages are chemosynthetic and cold-seep-dependent. The bathymetric ranges of extant molluscan species and the water temperature inferred from the stable oxygen isotope ratios of the authigenic carbonates suggest that lithofacies E was deposited in water depths of 150–240 m.

  • Chronostratigraphy of the Pliocenee-Pleistocene boundary in forearc basin fill on the Pacific side of central Japan: Constraints on the spatial distribution of an unconformity resulting from a widespread tectonic event

    Masayuki Utsunomiya, Chie Kusu, Ryuichi Majima, Yuichiro Tanaka, Makoto Okada

    Quaternary International ( Elsevier )  456   125 - 137   2017.11  [Refereed]

    Joint Work

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    The upper Ikego Formation (Pliocene) and the Urago Formation (Pliocene to Lower Pleistocene) have been examined for their lithostratigraphy, calcareous nannofossil biostratigraphy, and magnetostratigraphy. Both formations are forearc basin fills exposed on the Miura Peninsula on the Pacific side of central Japan. The boundary between these formations has been previously treated as the western extension of the Kurotaki Unconformity, which was considered to be related to widespread tectonic change at ca. 3 Ma in the Japanese forearc region. However, the presence of the unconformity on the Miura Peninsula remains unclear due to sparse lithostratigraphic and chronostratigraphic data around the boundary between the both formations. In the study area, the Ikego Formation consists mainly of sandy mudstone and the Urago Formation of sandstone and muddy sandstone; both formations contain numerous tuff beds. Key tuff beds and the last appearance of Discoaster tamalis have been identified in the upper Ikego Formation and the lower Urago Formation, allowing these formations to be considered conformable. The following continuous stratigraphic markers were identified (in ascending order): top of the Mammoth Subchronozone (3.21 Ma); base (3.13 Ma) and top (3.05 Ma) of the Kaena Subchronozone; last appearance of Discoaster tamalis (2.76 Ma); the widespread tuff bed KGP (ca. 2.5 Ma); and the last appearance of Discoaster pentaradiatus (2.41 Ma). Sedimentation rates are almost constant among these age-controlled horizons, which indicates continuous sedimentation from 3.2 to 2.4 Ma. The results indicate that the Kazusa Group conformably overlies the Miura Group on the Miura Peninsula, which provides a well-established continuous stratigraphic section for analyses of regional paleoenvironmental and tectonic evolution in the Japanese forearc region.


  • An extinct naticid species Glossaulax hyugensis (Shuto) (Mollusca:

    Fossils   ( 102 )   63 - 71   2017.09  [Refereed]

    Joint Work

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    A juvenile specimen of Glossaulax hyugensis (Shuto) was collected from the Lower Pleistocene Imaizumi Sandstone and Conglomerate Member in the Nojima Formation. This formation is in the lower part of the Kazusa Group, a forearc-basin-fill sequence exposed on the Pacific Ocean side of central Japan. The specimen was found in a 9-m-thick conglomeratic sandstone bed in a channel-fill sequence. G. hyugensis is haracteristic of the warm- and shallow-water Kakegawa fauna, which flourished on the Pacific Ocean side of southwestern Japan during the Late Pliocene to Early Pleistocene. The stratigraphic level at which the fossil was found is estimated to lie above the KGP tuff bed (2.5 Ma) and below the Olduvai subchronozone (1.97 Ma). This finding marks one of the latest fossil records for the species and suggests that it occurred for a long time period in the southern Kanto area, from the Late Pliocene to Early Pleistocene.

  • A record of the upper Olduvai geomagnetic polarity transition from a sediment core in southern Yokohama City, Pacific side of central Japan

    楠 稚枝,岡田 誠,野崎篤,間嶋隆一,和田秀樹

    Progress in Earth and Planetary Science   3   3 - 26   2016.09  [Refereed]

    Joint Work

    Web of Science DOI

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Presentations 【 display / non-display

  • Formation processes of cold seep authigenic carbonates developed around Callianassid burrows : Middle Pleistocene Kakinokidai Formation, Kazusa Group in Boso Peninsula, Chiba Prefecture, central Japan


  • Authigenic carbonates and burrows associated with cold-seep-depended assemblage from the middle Pleistocene Kakinokidai Formation, Kazusa Group, Chiba Prefecture.


  • A fossil cold-seep assemblage from the Pleistocene Shioda Formation, Nakatsu Group,central Japan


  • Benthic foraminiferal assemblages associated with chemosynthetic bivalves from the Plio-Pleistocene in the Leyte Island


  • Chronostratigraphy of the Calyptogena-bearing, Plio-Pleistocene Miura and Kazusa Groups,central Japan


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