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Volume 30 (1996)
- Issue 2 Pages 65-
- Issue 1 Pages 1-
Volume 30, Issue 2
Displaying 1-3 of 3 articles from this issue
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The Shibata Award
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Masatake HONDA1996 Volume 30 Issue 2 Pages 65-74
Published: October 30, 1996
Released on J-STAGE: December 18, 2016
JOURNAL FREE ACCESSBefore 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.View full abstractDownload PDF (874K)
The Geochemical Society of Japan Award for Young Researchers
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Kenichiro SUGITANI1996 Volume 30 Issue 2 Pages 75-89
Published: October 30, 1996
Released on J-STAGE: December 18, 2016
JOURNAL FREE ACCESSGeochemical 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.View full abstractDownload PDF (1390K)
Original Paper
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Naotatsu SHIKAZONO, Koichiro FUJIMOTO1996 Volume 30 Issue 2 Pages 91-97
Published: October 30, 1996
Released on J-STAGE: December 18, 2016
JOURNAL FREE ACCESSSimple coupled fluid flow-dissolution kinetics model for one-component and one-dimensional system was applied to estimate the ratio of surface area to mass of water (A/M) for granitic rock (Tsukuba, Japan). Dissolution rate of feldspar experimentally determined was used for the calculation. Estimated A/M values are in a range of 0.1〜6.0. This indicates that the width of fractures in granitic rock penetrated by groundwater is much wider than that of laboratory data. Therefore, it is suggested that the groundwater flow and interaction of groundwater with the country rocks are largely controlled by fractures in the country rocks, A/M and dissolution rate constants of silicates estimated based on field observations previously estimated for a catchment area were incorrect.View full abstractDownload PDF (720K)
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