The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 117, Issue 10
Displaying 1-5 of 5 articles from this issue
Review
  • Hiroyoshi Arai
    2011 Volume 117 Issue 10 Pages 547-564
    Published: October 15, 2011
    Released on J-STAGE: February 11, 2012
    JOURNAL FREE ACCESS
    Geological data such as the strike of bedding, paleocurrent directions, paleomagnetic directions, and the trend of mineral lineations are directional data defined by an angle from a reference direction. The main characteristic of such data is circularity in any reference direction (i.e. 0°=360°), which creates problems when analyzing the data statistically. In this regard, only directional statistics are adequate for dealing with directional data. This paper introduces the fundamental theory of circular statistics, a form of directional statistics that is restricted to data on a circumference, and presents practical methods with which to analyze circular data, including their graphical representation, descriptive statistics, the characteristics of circular uniform and von Mises distributions, tests of goodness-of-fit, and single- and multi-sample statistical tests. In addition, statistical software is considered with which to analyze circular data.
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Article
  • examples from the Miocene Kawabata and Karumai Formations, central Hokkaido, Japan
    Ryo Takahashi, Yasuyuki Kakihara, Junko Hara, Takeshi Komai
    2011 Volume 117 Issue 10 Pages 565-578
    Published: October 15, 2011
    Released on J-STAGE: February 11, 2012
    JOURNAL FREE ACCESS
    We investigated the leaching process of arsenic from Miocene sedimentary rocks (the Kawabata and Karumai Formations) and the change in leaching amount with weathering. The Kawabata and Karumai Formations show same clay mineral assemblage, smectite, chlorite and illite. Smectite is the dominant clay mineral in the Kawa-bata Formation, whereas chlorite and illite are dominant in the Karumai Formation. The leaching amount of arsenic shows an abrupt increase when the leachate pH exceeds 8.5. This leaching behavior suggests that arsenic adsorbed on ferric oxide and hydrous ferric oxide starts to leach with increasing pH of the leachate. The leachate pH is elevated by cation exchange between interlayer Na+ ions in smectite and H+ in the leachate. The high smectite content in the Kawabata Formation means that the leachate pH is high (up to 10.3) compared with that in the Karumai Formation (pH < 8.8). As a result, the leaching amount of arsenic from the Kawabata Formation (up to 0.074 mg/L) is larger than that from the Karumai Formation (< 0.006 mg/L). The exchangeable cation in smectite is mainly Na+ in unweathered rocks, whereas it in weathered rocks consists of other cations, such as Ca2+ and H+. Because the cation exchange capacity of Ca-smectite is smaller than that of Na-smectite, the cation exchange reaction is hard to occur between the leachate and weathered rocks. Consequently, the leachate pH does not rise and the leaching amount of arsenic is relatively small in the case of weathered rocks.
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Note
  • Yuji Ichiyama, Yasunori Hanafusa, Shinsuke Soma
    2011 Volume 117 Issue 10 Pages 579-584
    Published: October 15, 2011
    Released on J-STAGE: February 11, 2012
    JOURNAL FREE ACCESS
    The GANSEKI (Geochemistry and Archives of ocean floor rocks on Networks for Solid Earth Knowledge Integration) database, managed by JAMSTEC, houses information and geochemical data of rock samples collected during research cruises. The database can be searched by two methods: by dive and dredge sites identified on a map, and by metadata. Of the rocks in the database, archived samples housed at JAMSTEC are available for observation and analysis free of charge, if an application is made and accepted, and geochemical data in the JAMSTEC archives have been compiled in GANSEKI.
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Reports
  • Masaya Miyoshi, Takashi Yuguchi, Taro Shinmura, Yasushi Mori, Yoji Ara ...
    2011 Volume 117 Issue 10 Pages 585-590
    Published: October 15, 2011
    Released on J-STAGE: February 11, 2012
    JOURNAL FREE ACCESS
    We report on the petrography, whole-rock chemical composition, Sr isotope ratio, and K–Ar age of borehole core samples (310–630 m depth) of basement rocks from the northwestern caldera floor of Aso volcano, central Kyushu. The basement core is composed of granodiorite and hornfelsic pelitic-psammitic schist. Both the granodiorite and schist contain mainly quartz, plagioclase, K-feldspar, biotite, and opaque minerals. The granodiorite also contains rare hornblende. The schist has a banded structure, and the schist and granodiorite are migmatitic at a depth of 553 m. The granodiorite yields a K–Ar biotite age of 105 Ma. The petrographic characteristics and age of the granodiorite are similar to those of other basement granitic rocks in and around the Aso area (93–108 Ma). These observations indicate that the basement granitoids of the Aso area cooled at the same time as Cretaceous granitoids in central Kyushu.
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  • An example of the effective use of the “GANSEKI” database of rock samples from the deep sea floor
    Rie Nauchi, Tomoaki Morishita, Akihiro Tamura, Shoji Arai, Hiroshi Sat ...
    2011 Volume 117 Issue 10 Pages 591-596
    Published: October 15, 2011
    Released on J-STAGE: February 11, 2012
    JOURNAL FREE ACCESS
    Many samples of various rock types recovered directly from the ocean floor are housed at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The GANSEKI database, maintained by JAMSTEC, provides a record of submarine rock samples and is currently available on the Internet, enabling the user to search for specific types of submarine rock samples and their conditions, such as size, lithology and degree of alteration/weathering. We used the GANSEKI database to obtain submarine samples recovered from various tectonic settings, such as mid-ocean ridge, back arc, and forearc, and here we report on the major and trace element compositions of volcanic glasses from mid-ocean ridge settings.
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