The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
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Volume 120, Issue 5
Displaying 1-2 of 2 articles from this issue
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Article
  • Stratigraphy of the Tetori Group and the Jinzu Group(new name)in Gifu and Toyama prefectures, central Japan
    Masaki Matsukawa, Makiko Fukui, Yutaka Ogawa, Takeshi Tago, Kazuto Koa ...
    2014Volume 120Issue 5 Pages 147-164
    Published: May 15, 2014
    Released on J-STAGE: September 27, 2014
    DOIhttps://doi.org/10.5575/geosoc.2013.0011
    JOURNAL FREE ACCESS
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    We re-examined upper Mesozoic deposits around the border between Gifu and Toyama prefectures, central Japan, to resolve controversy regarding their stratigraphy. The deposits are divided into the Tetori Group and the overlaying the Jinzu Group (new lithostratigraphic unit). The Tetori Group includes marine deposits bearing Jurassic ammonites, whereas the Jinzu Group consists of terrestrial deposits. The Tetori Group is divided into the Magawa Formation and the conformably overlying Arimine and its stratigraphic equivalent, the Kiritani Formtion. The Jinzu Group, from bottom to top, is divided into the Ioridanitoge, Inotani and Shiroiwagawa Formations. The geological map of the area is revised to show the distribution of these six formations. The Tetori Group is assigned an age of Callovian to early Kimmeridgian based on ammonites, and the Inotani Formation of Jinzu Group is assigned an age of Aptian to Albian based on zircon-fission track dating with best-fit peak ages of 102.6 (−6.1, +6.5) , 111.6 (−6.2, +6.6), 112.5 (−11.0, +11.7) and 121.0 (−12.1, +11.7) . The Jinzu Group in the Jinzu Section in the eastern part of its distribution, is suggested to be Aptian and Albian, but the Tetori Group in the Hakusan Section in the western part of its distribution is suggested to be Bathonian to Barremian. Therefore, the Jinzu and Tetori Groups were probably deposited at different times.
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  • A reexamination of the stratigraphy of the Miocene Kuma Group, Shikoku, SW Japan: the “Shimosakabatoge Formation” and the“ Tomishige Formation”
    Masato Ochi, Takanobu Mamiya, Nao Kusuhashi
    2014Volume 120Issue 5 Pages 165-179
    Published: May 15, 2014
    Released on J-STAGE: September 27, 2014
    DOIhttps://doi.org/10.5575/geosoc.2014.0015
    JOURNAL FREE ACCESS
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    The stratigraphy of the lower-middle Miocene Kuma Group of Shikoku, southwestern Japan, was re-examined on the basis of geological field observations of the previously defined “Shimosakabatoge Formation” and the “Tomishige Formation.” The redefined Kuma Group consists of, in ascending stratigraphic order, the Furuiwaya Formation, composed mainly of clasts of Sambagawa metamorphic rocks, and the Myojin Formation, mainly sandstone and granite clasts. The lithofacies of the “Shimosakabatoge Formation” and its depositional age, as deduced from its clasts and the ages of igneous rocks that intrude the “formation”, suggest it is part of the Furuiwaya Formation. The previously proposed stratigraphy of the Kuma Group, in which the “Tomishige Formation” was placed at the top of the group, is questionable. The relationships between the Kuma Group and the lower Eocene Hiwadatoge Formation is revealed as an unconformity.
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