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 110, Issue 3
Displaying 1-6 of 6 articles from this issue
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Articles
  • Stratigraphy and geologic age of the Middle Permian in the Kamiyasse-Imo district, Southern Kitakami Massif, Northeast Japan
    Akihiro Misaki, Masayuki Ehiro
    2004 Volume 110 Issue 3 Pages 129-145
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.129
    JOURNAL FREE ACCESS
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    The Permian strata, distributed in the Kamiyasse-Imo district to the north of Kesennuma, Southern Kitakami Massif, Northeast Japan, are divided into the Nakadaira, Hosoo, Kamiyasse and Kurosawa Formations in ascending order. The Nakadaira Formation is composed mainly of limestone and sandstone, Hosoo Formation mainly of black mudstone, Kamiyasse Formation mainly of limestone, calcareous mudstone and sandstone, and Kurosawa Formation mainly of black mudstone. The Kamiyasse Formation shows a marked lateral variation in lithofacies, and limestone and calcareous mudstone are dominant in the northern area, whereas sandstone dominates in the southern area.
    From the Hosoo Formation, such ammonoid fossils as Demarezites from the middle part and Waagenoceras and Paraceltites from the upper part, were newly discovered. The upper part of the Hosoo Formation and lowermost part of the Kamiyasse Formation yield a fusulinoidean genus Pseudodoliolina. Monodiexodina matsubaishi, which is an index fusulinoidean species of the lower Middle Permian M. matsubaishi Zone, occurred from the lower to upper part of the Kamiyasse Formation. It was made clear for the upper limit of its range to reach in the lower part of the Lepidolina multiseptata Zone.
    Based on the fusulinoidean and ammonoid biostratigraphic data, the Nakadaira Formation to the lower part of the Hosoo Formation, middle part of the Hosoo Formation, upper part of the Hosoo Formation to the lower part of the Kamiyasse Formation and upper part of the Kamiyasse Formation to the lower part of the Kurosawa Formation are correlatable with the Sakmarian to Kungurian, Roadian, Wordian and Capitanian Stages, respectively.
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  • Megafossil-bearing mudstone blocks in the Oriai Formation of the Upper Jurassic Imaidani Group in the Shirokawa area, Ehime Prefecture, Southwest Japan
    Masahiko Takei, Atsushi Matsuoka
    2004 Volume 110 Issue 3 Pages 146-157
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.146
    JOURNAL FREE ACCESS
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    The mode of occurrence and lithofacies were examined in detail for some megafossil-bearing blocks found in mudstones of the Oriai Formation, in the lower part of the Imaidani Group in the Shirokawa area, western Shikoku, which is an equivalent of the Torinosu Group. These sandy siltstone blocks have irregular contacts with mudstone. These blocks are composed mostly of intensively bioturbated, massive or poorly-stratified sandy siltstone, and yield megafossils, such as brachiopod, bivalve, echinoid, ammonite, plant fossils and so on. Ammonite Hybonoticeratid species newly found from a few blocks indicate middle Kimmeridgian to early Tithonian age. Microscopic observation of HF-etched surface of argillites shows that the grain-size of plant debris contained in the sandy siltstone blocks are larger than those in the surrounding mudstone.
    The mode of occurrence of the sandy siltstone blocks and differences in litho-and biofacies between the blocks and the surrounding mudstone indicate that the sandy siltstones are not interbeded with mudstone but are included as allochthonous blocks. These blocks were originally accumulated in shallower marine, probably environment and were brought into a deeper environment of shelf slope. The mixing of the allochthonous blocks with surrounding mudstones took place in early Tithonian.
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  • Volcanic history of the middle Pleistocene Older Ontake Volcano, Central Japan
    —Inferences from tephrostratigraphy and petrography—
    Yoshihiro Takeshita
    2004 Volume 110 Issue 3 Pages 158-174
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.158
    JOURNAL FREE ACCESS
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    Ontake Volcano is situated at the southern margin of the Norikura volcanic chain, Central Japan. The volcano consists of the Older (0.78—0.39 Ma) and Younger (0.09—0.02 Ma) Ontake Volcanoes with long dormancy between them.
    Lithofacies and heavy mineral assemblage of almost all of the tephra (air fall tephra and pyroclastic flow deposits) from the Older Ontake Volcano are described. Petrographic studies of some of them have been further carried out; such features as grain compositions, heavy mineral compositions and chemical compositions of hornblende and pyroxenes. Tephrostratigraphy of the Older Ontake Volcano was established using stratigraphic relations with the dated lavas, and the petrographic features of tephra. Conclusively, the activity of the Older Ontake Volcano was divided into Tephra Stage (before 0.78—0.64 Ma) and Lava Stage (0.64—0.39 Ma) based on the mode of eruption; the Tephra Stage being characterized by effusion of many air fall tephra and pyroclastic flows, whereas the Lava Stage contains many thicker lavas. The Tephra Stage is further subdivided into H Substage (before 0.78 Ma), PH Substage (0.78—0.70 Ma) and OP Substage (0.70—0.64 Ma) by the assemblage of dominant heavy minerals in the air fall tephra as follows: H Substage; green hornblende, PH Substage; pyroxenes and brown hornblende, OP Substage; olivine and pyroxenes. Ages of each stage and substage were inferred from the stratigraphic relations with the dated lavas. Each of the stages and substages is distinguishable not only by heavy mineral assemblages, but also by chemical compositions of hornblende and pyroxenes in the air fall tephra.
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  • Geology and integrated chronostratigraphy of the Miocene marine sequence in the Tomioka area, Gunma Prefecture, central Japan
    Masaki Takahashi, Hiroki Hayashi
    2004 Volume 110 Issue 3 Pages 175-194
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.175
    JOURNAL FREE ACCESS
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    Previously reported planktonic microfossils and radiometric ages of volcaniclastic layers of the Miocene marine sequence in the Tomioka area are reviewed. Based on the biostratigraphic and radiometric ages, sediment accumulation history and geologic structure, more than 3, 600m-thick marine sequence of the Tomioka area is divided into lower Tomioka Group (partly modified) and upper Annaka Group (newly difined). The Annaka Group covers the Tomioka Group, unconformably (Niwaya Unconformity). High sedimentation rate of 200 cm/1, 000yr. characterizes the Tomioka Group. In contrast, sandstone to sandy siltstone succession of the upper half of the sequence (Annaka Group) shows relatively slow sedimentation rate of less than 40 cm/1, 000yr. High sedimentation rate of the Itahana Formation is due to the development of submarine delta related to regression.
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