The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 113, Issue 6
Displaying 1-6 of 6 articles from this issue
Articles
  • Shun Chiyonobu, Tokiyuki Sato, Ken'ichi Ishikawa, Makoto Yamasaki
    2007 Volume 113 Issue 6 Pages 223-232
    Published: 2007
    Released on J-STAGE: February 01, 2008
    JOURNAL FREE ACCESS
    We discuss the uppermost Cenozoic calcareous nannofossil biostratigraphy of two hot spring wells (Toshimaen and Tokyo-dome) located in central part of Tokyo. The lithology of the upper Pliocene to lower Pleistocene is mainly composed of silty sandstone to sandy siltstone, pumiceous tuff, and siltstone which are correlated to the Kazusa Group in the Boso Peninsula.
    Calcareous nannofossil assemblages of the Tokyo-dome well are characterized by abundant occurrences of Reticulofenestra spp. (small form). Discoaster spp., which indicates the early to late Pliocene age, and the early Pliocene marker species Reticulofenestra pseudoumbilicus are found in the lower part of the section. Four early Pleistocene nannofossil datums between 1.73 Ma and 1.21 Ma are traceable to the lower part of the section. Nannofossil assemblages found in the Toshimaen well are dominated by the latest Pliocene to early Pleistocene species. Four Quaternary nannofossil datums which are recognized in the Tokyo-dome well are also detected in the lower part of the sequence. This indicates that the Quaternary sequences found in both wells clearly correlate to the lower Pleistocene Kiwada Formation of the Boso peninsula. The middle to upper Pleistocene marine sequence above the Kiwada Formation was not detected in these wells.
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  • Kenji Kashiwagi
    2007 Volume 113 Issue 6 Pages 233-248
    Published: 2007
    Released on J-STAGE: February 01, 2008
    JOURNAL FREE ACCESS
    The Inumodorikyo Complex of the Southern Chichibu Belt in the eastern Kii Peninsula, Southwest Japan, consists of siliceous claystone, chert, dark green siliceous mudstone, and terrigenous clastic rocks, and is subdivided into the Nomata Belt on the north and Kuwanokidani Belt on the south by the north-dipping Nomata Thrust. Radiolarians recovered from the terrigenous clastic rocks show that the ages of the complex in the Nomata and Kuwanokidani Belts are, respectively, middle Bathonian to late Callovian (late Middle Jurassic) and late Callovian to Oxfordian (latest Middle to early Late Jurassic).
    The structural analysis of the crush zone and fault rocks suggest that the Nomata Thrust really has a dominant reverse-slip component. NNE- to NE-trending high-angle faults cut the ENE-trending structures of the Inumodorikyo Complex as well as the middle Late Cretaceous accretionary complexes on the south. Moreover the strata of lower structural horizon widely expose on the east of the Nishiyamagawa - Kasagigawa Fault, which is one of the high-angle faults. Hence the high-angle faults are east-side-up, dip-slip faults and were likely active during latest Cretaceous to Paleogene time.
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  • Hitoshi Nishiwaki, Takamoto Okudaira
    2007 Volume 113 Issue 6 Pages 249-265
    Published: 2007
    Released on J-STAGE: February 01, 2008
    JOURNAL FREE ACCESS
    Hatsuse plutonic complex in the Ryoke metamorphic belt, central Kinki Province, SW Japan, is composed mainly of the Cretaceous gneissose biotite granodiorite and hornblende gabbros. The biotite granodiorite is a syn-kinematic pluton during the deformation forming upright folds and the hornblende gabbros are syn-plutonic dykes intruded subparallel to the gneissosity of the surrounding granodiorite. The trends of the gneissose structure in the granodiorite and of the lithological boundaries between the granodiorite and gabbros exhibit basin structure possibly divided into major E-W trending synform and minor N-S trending synform. The gneissose structure in the granodiorite is defined mainly by the alignment of the long-axis of the biotite clots. Based on the microstructural analyses, the gneissose structure was formed by the magmatic to submagmatic flow during the emplacement of the granodiorite magma. Based on the amphibole chemistry, emplacement depth of the granodiorite magma was estimated to be 450-600 MPa that corresponds to crustal depth of about 20 km. In the granodiorite, since high-temperature plastic deformation conditions determined by the c-axis fabric of quartz grains (X-maximum and type-II crossed girdle patterns) are observed in the quartz grains and the maximum elongation directions between the magmatic/submagmatic flow and the high-temperature plastic deformation structures are consistent with each other, the deformation related to the emplacement of the granodiorite magma lasted just after the solidification of the magmas. The basin axis of the major E-W trending synform is parallel to the regional upright folds observed elsewhere in the Ryoke metamorphic belt ; the emplacement of the plutonic complex may be governed by the regional stress fields to form the upright folds in the Ryoke metamorphic belt.
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Short Articles
  • Makoto Saito, Shunsuke Kawakami, Masatsugu Ogasawara
    2007 Volume 113 Issue 6 Pages 266-269
    Published: 2007
    Released on J-STAGE: February 01, 2008
    JOURNAL FREE ACCESS
    Red mudstone in the accretionary complex in Yakushima Island is dated as middle Middle to early Late Eocene by co-occurrences of Dictyoprora mongolfieri, Theocyrtis cf. perpumila, Calocycloma cf. ampulla.
    As most of the accretionary complex in Yakushima Island underwent contact metamorphism by Middle Miocene Yakushima Granite, no fossils were obtained from the accretionary complex. We extracted radiolarian fossils from the non-metamorphosed red mudstone and a hard mudstone nodule included in mudstone in the eastern part of the Yakushima Island. The radiolarian fossils from the red mudstone are poorly preserved but sufficient for age determination.
    Compared with the Hyuga Group of the Shimanto accretionary complex in southeastern Kyushu, which the original stratigraphy are known well, the red mudstone of Yakushima Island is just younger than the early Middle Eocene red mudstone with basalt.
    Although the turbidite of the Hyuga Group is middle Middle Eocene in southeastern Kyushu, the age of the whole Hyuga Group's terrigenous sediments is Eocene to Early Oligocene. This implies that there is some age difference between the red mudstones. As the lithology and structure of the accretionary complex in Yakushima Island is very similar to that in southeastern Kyushu, the accretionary complex in Yakushima Island is compared to the Hyuga Group.
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  • Tetsuya Tokiwa, Yoshinori Mori, Hiroyuki Suzuki, Kohsuke Niwa
    2007 Volume 113 Issue 6 Pages 270-273
    Published: 2007
    Released on J-STAGE: February 01, 2008
    JOURNAL FREE ACCESS
    The Ryujin Formation, occupying a wide area in the Cretacesous Hidakagawa Group of Shimanto Belt in the Kii Peninsula, Southwest Japan, has been considered to be an accretionary complex of late Campanian in age. Radiolarian fossils of the age evidence have been found from only the western part of the Hidakagawa Group. In this article, we report radiolarian fossils of the Amphipyndax tylotus interval zone newly found from the central part of the Hidakagawa Group. Therefore the geologic age of the Ryujin Formation was firmly established to be a late Campanian.
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  • Noritoshi Suzuki, Satoshi Yamakita, Satoshi Takahashi, Masayuki Ehiro
    2007 Volume 113 Issue 6 Pages 274-277
    Published: 2007
    Released on J-STAGE: February 01, 2008
    JOURNAL FREE ACCESS
    A Bajocian to Early Bathonian (Middle Jurassic; Striatojaponocapsa plicarum Zone) radiolarian fauna was recovered from carbonate manganese nodules in siliceous mudstone of the Otori Formation in the North Kitakami Belt (Kuzumaki-Kamaishi Subbelt), Northeast Japan. The Otori Formation mainly consists of white to grey chert, and is marked by Permian red chert and Bajocian to lower Bathonian siliceous mudstone, although their original stratigraphic relationships have not been understood. This formation is tectono-stratigraphically correlatable to the Ryokamiyama Chert Unit of the Ohirayama Unit in the Southern Chichibu Belt in the Kanto Mountains.
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