地球化学
Online ISSN : 2188-5923
Print ISSN : 0386-4073
ISSN-L : 0386-4073
30 巻, 2 号
選択された号の論文の3件中1~3を表示しています
日本地球化学会柴田賞受賞記念論文
  • 本田 雅[タケ]
    1996 年 30 巻 2 号 p. 65-74
    発行日: 1996/10/30
    公開日: 2016/12/18
    ジャーナル フリー
    Before the fall on the earth, iron and stone meteorites have been irradiated in space by so-called Galactic "cosmic rays", high energy protons and neutrons, and contain various species of stable and radioactive nuclides. The first discovery of the products was that of Helium-3, 3He, which is a stable isotope of helium and it is up to about 30% of He-4 contents in iron meteorites. The He-3 consists of direct products of He-3 and also those by an indirect path via H-3 which is produced primarily and decayed into He-3. Therefore just after the fall the radioactivity of tritium can be observed. When continuous irradiation has continued for longer than the half-life of the radioactive nuclides. the activities will saturate and reach to a radioactive equilibrium, and the level of the decay rate becomes equal to the production rate in space. In this article we may observe the historical developments of studies in this field. Some datailed descriptions will be given especially in the examples of unexpected developments and the importance of related faint information.
日本地球化学会奨励賞受賞記念論文
  • 杉谷 健一郎
    1996 年 30 巻 2 号 p. 75-89
    発行日: 1996/10/30
    公開日: 2016/12/18
    ジャーナル フリー
    Geochemical indicators for origins and sedimentary environments of marine sediments and siliceous sedimentary rocks are reviewed. Al2O3/TiO2 and Zr/TiO2 values are useful indicators for sources of detrital materials in sediments, because these values in igneous rocks change systematically (acidic > intermediate > mafic). MnO/TiO2 and Co/TiO2 values and Co-Ni-Zn diagram, on the other hand, are useful for discrimination between pelagic sediments and hemipelagic ones. Pelagic sediments deposited under oxic environment are characterized by high MnO/TiO2 and Co/TiO2 values and enrichment of Co and Ni relative to Zn, compared with hemipelagic sedmiments. In addition to these indicators, stratigraphic variation of MnO and CO2 (derived from carbonate minerals) concentrations can discriminate between pelagic sediments and hemipelagic ones. In hemipelagic sediments where diagenetic remobilization of manganese is active, MnO and CO2 concentrations often show covariation and manganese carbonate bands (rhodochrosite-concentrated layers) are found at depths. It should be also noted that these geochemical indicators are, in some cases, modified by diagenesis and subaerial alteration. Careful application of these indicators to analyses of sedimentary paleoenvironments is required.
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