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 115, Issue 4
Displaying 1-5 of 5 articles from this issue
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Review
  • Fluid mud: Distinctive features and implications for genetic stratigraphy
    Naohisa Nishida, Makoto Ito
    2009 Volume 115 Issue 4 Pages 149-167
    Published: April 15, 2009
    Released on J-STAGE: September 04, 2009
    DOIhttps://doi.org/10.5575/geosoc.115.149
    JOURNAL FREE ACCESS
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    Fluid mud, which is defined as fluid containing more than 10 g/L of suspended sediments, is formed mainly by (1) the development of turbidity maximum in tide-influenced depositional environments, particularly in estuaries and distributary channels; or by (2) high sediment discharge at river mouths during flood events. Muddy deposits, which are formed from fluid mud, are characterized mainly by massive facies and clay fabric herein named “granular structure”. Some fluid-mud deposits in coastal and shallow-marine successions have been interpreted to represent environments located further offshore than those associated with sandy deposits. Thus, the identification of fluid-mud deposits in stratigraphic records is crucial for a better understanding of depositional environments and processes.
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Articles
  • Permian brachiopods from the Tsunemori Formation of the Akiyoshi area, southwest Japan:
    Fossil evidence for the accretion site of the Akiyoshi Terrane
    Jun-ichi Tazawa, Masayuki Fujikawa, Yasuhiro Ota
    2009 Volume 115 Issue 4 Pages 168-176
    Published: April 15, 2009
    Released on J-STAGE: September 04, 2009
    DOIhttps://doi.org/10.5575/geosoc.115.168
    JOURNAL FREE ACCESS
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    The Tsunemori fauna, from pebbly shale in the upper part of the Tsunemori Formation (Changhsingian) in the Akiyoshi area, southwest Japan, consists of 15 species of Middle to Late Permian brachiopods in 15 genera. The fauna contains both Boreal and Tethyan elements, and is closely allied with the Nabekoshiyama fauna from the upper Toyoma Formation of the South Kitakami Belt, northeast Japan, and the Kawahigashi fauna from the upper Maizuru Group of the Maizuru Belt, southwest Japan, in having the Lamnimargus-Megousia-Eolyttonia assemblage. Based on these findings, the accretion site of the Tsunemori Formation was probably located on the trench or inner trench slope along the eastern margin of North China (Sino-Korea), close to the South Kitakami and Maizuru areas, during the late Middle to late Late Permian (Capitanian-Changhsingian).
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  • Correlation of late Miocene tephra beds in the central area of Niigata Prefecture, northeast Japan
    Hironori Hiranaka, Yukio Yanagisawa, Katsuki Kurokawa
    2009 Volume 115 Issue 4 Pages 177-186
    Published: April 15, 2009
    Released on J-STAGE: September 04, 2009
    DOIhttps://doi.org/10.5575/geosoc.115.177
    JOURNAL FREE ACCESS
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    Upper Miocene tephra beds considered likely to represent a widespread tephra were found in the Tsugawa (Aga Town), Nanatani (Kamo City), and Sumon (Uonuma City) areas of central Niigata Prefecture, northeast Japan. The Otbt Tephra Bed in the Nomura Formation at Tsugawa, the Dtbt Tephra Bed in the Minamiimogawa Formation at Kamo, and the Isbt Tephra Bed in the Tsunagi Formation at Sumon are correlated with one another based on petrographic characteristics, the chemical composition of volcanic glass shards, and diatom biostratigraphy. These tephra beds are characterized by extremely low MgO (<0.01 wt.%) and CaO (<0.40 wt.%) contents in volcanic glass shards. The three tephra beds are assigned to the lowest part of the Neogene North Pacific diatom zone NPD 5D, between diatom biohorizons D56 (10.0 Ma) and D57 (9.4 Ma), with an estimated age of 9.9 Ma.
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Short Article
  • First occurrence of Paleogene pteropods (Gastropoda; Thecosomata) from Japan
    Yusuke Ando, Atsushi Ujihara, Takashi Ichihara
    2009 Volume 115 Issue 4 Pages 187-190
    Published: April 15, 2009
    Released on J-STAGE: September 04, 2009
    DOIhttps://doi.org/10.5575/geosoc.115.187
    JOURNAL FREE ACCESS
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    More than 100 pteropod specimens were collected from each of the Eocene Shikiyama and Oniike formations in the Amakusa area, Kumamoto Prefecture, Southwest Japan. These fossils constitute the first Paleogene pteropod record from Japan. The pteropods from the Shikiyama Formation consist of five species, including Limacina canadaensis Hodgkinson, L. pygmaea (Lamarck), and Praehyalocylis annulata (Tate). The pteropods from the Oniike Formation consist of six species, including Limacina canadaensis, L. lotschi (Tembrock), Creseis hastata (Meyer), C. simplex (Meyer), and Praehyalocylis annulata. Both of these pteropod faunas are characterized by the predominance of Limacina in species diversity and specimen abundance. The faunas are similar to the pteropod faunas from the Middle to Upper Eocene of Europe and the east coast of North America in terms of generic composition and the predominance of Limacina.
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