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Volume 34 (1995)
- Issue 5 Pages 335-
- Issue 4 Pages 279-
- Issue 3 Pages 125-
- Issue 2 Pages 65-
- Issue 1 Pages 1-
Volume 34, Issue 4
Displaying 1-6 of 6 articles from this issue
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Naoko Kitada, Kiyoshi Wadatsumi, Shinji Masumoto1995 Volume 34 Issue 4 Pages 279-288
Published: October 31, 1995
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSIsothermal Plateau Fission Track (ITP-FT) method was applied to samples of obsidians and glass shards from tephra-layers. This method uses one-step pre-annealing, which is combined with size-correction and plateau-correction techniques. An age is determined at a plateau phase. Plateau phases usually occur when induced and spontaneous mean track diameters are coincident, or when induced and spontaneous track density ratios are constant. In the ITP-FT method, plateau phases are determined based only on the coincidence of induced and spontaneous mean track diameters.
To improve on the ITP-FT method, it is necessary to estimate the reliability of plateaus obtained from the track diameter method by examining density ratios. In this study, 165°C annealing was carried out in order to reduce annealing time and categorize the relation between a track size coincidence “plateau” and a spontaneous/induced density ratio's constant “plateau”. The results indicate that the plateau phase determined by the coincidence of induced and spontaneous mean track diameters appears after the plateau phase determined by track density ratios. These co-plateau phases are appear after 5 days of annealing. As the result of this experiment, it is concluded that the coincidence of mean track diameters defines a more prominent and strict plateau phase than the track density ratio.
Based on the above results, it is suggested that 5 to 10 days annealing at 165°C is adequate to produce plateau stability and mean track diameter coincidence and is the most suitable condition when the ITP-FT method is applied.View full abstractDownload PDF (1341K) -
Tadamichi Oba, Masafumi Murayama, Eiji Matsumoto, Toshio Nakamura1995 Volume 34 Issue 4 Pages 289-296
Published: October 31, 1995
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSRadiocarbon ages were determined from eight depths in two piston cores recovered from the Oki Ridge in the Japan Sea using accelerator mass spectrometer (AMS). In the present study only shells of a planktonic foraminifera, Globigerina umbilicata, were used for the 14C dating. The AMS-14C ages at the last glacial maximum period are about 4, 500 years younger than the 14C ages obtained by the previously used method, which involved gathering CO2 gas evolved from the reaction of the sediment with hydrochloric acid. The age difference is due to the presence of dead carbon in the bulk carbonate, accounting for as much as 40% of the total carbonate, and presumably derived from eolian dusts drifting into the Japan Sea during the last glacial age. According to this new AMS dating, the age of the lowest salinity of the surface water in the Japan Sea is about 15, 000 years BP.View full abstractDownload PDF (977K) -
Tadashi Nakajima, Junko Fujii1995 Volume 34 Issue 4 Pages 297-307
Published: October 31, 1995
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSPaleomagnetic measurements have been carried out on the Aira Tn tephra, which erupted about 22, 000-25, 000 yrsBP from Aira caldera in Southern Kyushu. The tephra is distributed widely in Japan, and is the important marker bed in the Quaternary research. We collected about 800 oriented samples at 44 sites of outcrops of the tephra. The stable component of remanent magnetization was isolated from all samples through stepwise alternating field demagnetization up to 70mT. The direction of stable component was obtained using principal component analysis, anchored to the origin of Zijderveld diagram.
The VGPs obtained from different sites agree well with one another, which, means that their remanent magnetizations were acquired under the same geomagnetic dipole field (DF) at the time of eruption of the tephra. The pole of the DF can be assumed to be located on the all-mean VGP (Long=104.6°W, Lat=81.1°N, A95=1.3, N=44). Declinations and inclinations over the Japanese islands calculated from the pole range between 8°E and 10°E, and between 45° and 55°, respectively. The surveyed area was divided into 10 regions, and the local geomagnetic field (LF) direction of individual regions was calculated from the regional mean VGP. The difference between the DF and the LF direction at each region is less than 3°, except in Okayama Prefecture and Toyama Prefecture. The declination of the LF in Okayama Prefecture is deflected westerly by about 5° from those in the nearby regions, and the inclination of the LF in Toyama Prefecture is steeper by about 7° than those in the nearby regions. These local anomalous directions might be caused by the non-dipole field in the regions.View full abstractDownload PDF (1292K) -
Shigehiro Katoh, Kotaro Yamagata, Koji Okumura1995 Volume 34 Issue 4 Pages 309-313
Published: October 31, 1995
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThe Shikotsu and Kuttara volcanoes in southern Hokkaido often erupted violently during the Late Pleistocene and provided many time-marker tephra layers which are widely distributed to the east of them. These layers are important for the Quaternary tephrochronological studies in the Ishikari Lowland, Hidaka District, and Tokachi Plain. The nomenclature of the tephra layers here are based on Yamagata (1994).
We obtain there new radiocarbon dates by accelerated mass spectorometry (AMS-14C dates): 39, 290±970, 45, 500±2, 000, and 49, 800±3, 100yrs BP for Kt-1, Kt-Tk, and Ssfa·Ssfl, respectively. By correlating these and other AMS-14C dates in previous studies, we estimate the eruption ages of tephra layers from the two volcanoes as follows: ca. 40ka for Kt-1, 44-48ka for Kt-Tk, 47-51ka for Kt-3, and 47-53ka for Ssfa·Ssfl. In addition, the dates of Spfa 1 and Z-M are estimated 38-39ka and 42-44ka based on their stratigraphical relationships with the above tephra layers.View full abstractDownload PDF (711K) -
[in Japanese], [in Japanese], [in Japanese], A. Arkhangerov, V. Kunits ...1995 Volume 34 Issue 4 Pages 315-317
Published: October 31, 1995
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSDownload PDF (969K) -
K. Saijo, D. Nagaoka, M. Fukuda, A. Arkhangerov, V. Kunitsky1995 Volume 34 Issue 4 Pages i-ii
Published: October 31, 1995
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSDownload PDF (1267K)
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