The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 109, Issue 1
Displaying 1-9 of 9 articles from this issue
  • Akira Furusawa
    2003 Volume 109 Issue 1 Pages 1-19
    Published: January 15, 2003
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The refractive indices of volcanic glass and orthopyroxene in the tephra layers mainly erupted from Iwate Volcano overlaying the Toya Ash around 100 ka activity were determined by means of the temperature variable type refractive index measuring device, MAIOT. Because MAIOT enables us to measure precise and rapid refractive indices on the above minerals, it is useful to distinguish each tephra layer around the studied area. The color, shape and amount of microphenocrysts of volcanic glass were also classified by microscopic identification. On the basis of these petrographic characteristics, identification of each tephra layer has been clarified. In particular, the Yukiura Pumice layer, which is thought to be one homogeneous layer, could be divided into three different pumice layers showing different pumice layers showing different refractive indices of glass. One unknown tephra layer situated on the Toya Ash is identified as one of the tephra originated in the Iwate Volcano by the comparison of refractive indices with the lists in this paper. On the foot of Iwate Volcano, the Aira Tn volcanic ash layer (AT) originated Aira caldera, southern Kyushu was intercalated in the Takizawa 1 Scoria in the Shibutami Volcanic Ash member. The Towada Chuzeri pumice was also interbeded in the humus bed just below the Sugo Scoria in the Wakare Volcanic Ash member.
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  • Junko Komatsubara, Yoshihisa Hiroki, Ryo Matsumoto
    2003 Volume 109 Issue 1 Pages 20-29
    Published: January 15, 2003
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Sedimentary facies and total organic carbon and total sulfur concentrations of mudstones of the lower Miocene Nojima Group confirm that the Nojima Group has been deposited in a fresh-water environment before a major marine incursion into the Japan Sea. We identified nine sedimentary facies, which were grouped into seven facies associations, and recognized three depositional environments : lacustrine, deltaic, and fluvial. Total sulfur concentrations are much lower than 0.3wt%. Total organic carbon concentrations are up to 5.61wt%. The carbon/sulfur ratios show typical values in fresh-water sediments. The sedimentary facies and geochemical analysis indicate that the most of Nojima sedimentary basin was filled with lacustrine, deltaic and fluvial fresh-water deposits. Although no sample was obtained from the upper most part of the Nojima Group (Minamitabira Formation) because of lack of exposure, marine fauna in the uppermost part of the group reported by previous researchers possibly indicate a transgression caused by a combination of a global sea-level rise and an active tectonic activity during the opening of the Japan Sea.
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  • Ken Tsuchiya, Takashi Hasegawa, Lisa M. Pratt
    2003 Volume 109 Issue 1 Pages 30-40
    Published: January 15, 2003
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Although inoceramid zones are important chronostratigraphic tools for the Japanese Upper Cretaceous, some recent studies suggested chronostratigraphic discrepancies between mega-and microfossil biochronologies from the Yezo Group in Hokkaido, Japan. Carbon isotope profiles from organic matters obtained in this study from three sections of Hokkaido resemble to isotope profiles from carbonate in England calibrated by biochronology with Tethyan index fossils. The carbon isotope profiles from the Kotanbetsu and Oyubari areas show negative shift segment through the Inoceramus hobetsensis Zone, stable value segment from the upper part of the Inoceramus hobetsensis Zone through the Inoceramus teshioensis Zone and gradual positive migration segment in the Inoceramus uwajimensis Zone and the Inoceramus amakusensis Zone in an acending order. This stratigraphic pattern of carbon isotope curve corresponds to the pattern characterizing the middle Turonian to lower Santonian for the England section. Short term positive excursions (as large as 0.5∼1.0‰) superimposed on the long term fluctuation are observed in the Inoceramus hobetsensis Zone from the three sections. They may be potential stratigraphic markers correlative to the similar positive excursions observed in many European sections.
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  • Yuichiro Miyata, Masaya Koge
    2003 Volume 109 Issue 1 Pages 41-47
    Published: January 15, 2003
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Sound-producing sand grains called singing sands or squeaking sands constitute puzzling physical phenomena. They produce manifest acoustic emissions of 500 to 1000 Hz when sheared. Eolian quartz sand material were used for the examination of friction characteristics as well as surface textures with progressive abrasion by washing and polishing. Sufficiently polished quartz sands produced squeaking sound and demonstrated increases of porosity, angle of repose and angle of internal friction. However, they show lower friction when submerged in water. It is probably because that the inter-solid friction due to adhesion or pressure solution was lowered by the water film between the grains. In addition, well-polished quartz sands demonstrated a distinct cyclic stick-slip motion under slow shear using less stiff loading system. The higher inter-solid friction and the cyclic stick-slip motion are strongly suggested as the cause of singing sands rather than roundness or sorting of sands.
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  • Itsuki Suto, Masaki Takahashi, Yukio Yanagisawa
    2003 Volume 109 Issue 1 Pages 48-62
    Published: January 15, 2003
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Diatom biostratigraphy is first established for the Miocene marine sequence of the Tsuchishio Formation distributed along the Arakawa River, Aketo stratigraphic section, in the northern part of the Hiki Hills area, central Japan. Thirty-two samples yield age diagnostic diatom fossils, which indicate the sequence to be restricted between two diatom biohorizons, the acme/last common occurrence of Denticulopsis hustedtii (D 55.8 : 10.1 Ma) and the first occurrence of Denticulopsis dimorpha (D56 : 10.0 Ma) in the uppermost part of the Thalassiosira yabei Zone (NPD 5 C). The age-determination based on the high resolution diatom biostratigraphy allows precise correlation to the other several Miocene marine sequences in central Japan. The present correlation model, especially, shows that regression facies from the hemipelagic Tsuchishio Formation to the deltaic Yagii Formation delayed ca. 1.5 m.y. than the similar facies change from the Haraichi Formation to the Itahana Formation in the Tomioka area, Gunma Prefecture.
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  • Shusaku Yoshikawa, Hideo Watanabe, Jun Inoue
    2003 Volume 109 Issue 1 Pages 63-70
    Published: January 15, 2003
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The Late Pleistocene Maibara and Kaisaka Loam Formations, consisting of weathered eolian deposits, are widely distributed in Niigata and Nagano Prefectures, Central Japan. Plants preserved fossil-charcoal are identified from these formations. The fossils consist of small angular fragments (mostly 1 to 50 mm diameters), a dull black lustre, brittle fracture and homogenised cell wall. H/C thermometer indicates that the fossil charcoal fragments were charred in the range 430-460°C. Stratigraphically, the fossil charcoal, indicating the occurrence of wildfire, have been recognized at three stratigraphic levels, called Tsunan-1, Tsunan-2 and Tsunan-3 fossil charcoal horizons, in these formations. Tsunan-1 fossil charcoal exists at the horizon between the M 4 and M 3 tephra bed (ca.110-120 ka), and is widely distributed in Niigata and Nagano areas, for a distance of more than 50 km. Tsunan-2 fossil charcoal occurs at a horizon of immediately above the M 6 tephra bed (ca.90-100 ka), and is sporadically distributed in Niigata and Nagano areas, along the Shinano River for a distance of about 30 km. Tsunan-3 fossil charcoal occurs at a horizon of immediately below the K 0 tephra bed (ca. 70 ka), and is distributed in Niigata and Nagano areas, for a distance of more than 20 km. We conclude that these fossil charcoal horizons are useful for understanding the wildfire history during late Quaternary and are important as stratigraphic marker horizons.
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  • Makoto Saito, Seiichi Toshimitsu
    2003 Volume 109 Issue 1 Pages 71-74
    Published: January 15, 2003
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Early Cretaceous Tomochi Formation in central Kyushu is occupied by northern margin of the Chichibu Belt along the Usuki-Yatsushiro Tectonic Line. The Tomochi Formation is shallow marine sediment and correlative with the Monobegawa Group in Shikoku. The Tomochi Formation unconformably covers the Hirodaira Unit composed of melange. We have discovered Late Permian radiolarian fossils from terrigenous sediments of the Hirodaira Unit. We clarified that the correlative of the Monobegawa Group in Kyushu covers the Permian accretionary complex same as in central Shikoku. And it has revealed that the Permian accretionary complex occurs in two rows around the area.
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  • 2003 Volume 109 Issue 1 Pages 76
    Published: 2003
    Released on J-STAGE: November 26, 2010
    JOURNAL FREE ACCESS
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  • Akira Ishiwatari
    2003 Volume 109 Issue 1 Pages I-II
    Published: 2003
    Released on J-STAGE: December 14, 2010
    JOURNAL FREE ACCESS
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