| Project/Area Number |
12640443
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geology
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| Research Institution | Hiroshima University |
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Principal Investigator |
KANO Akihiro Hiroshima Univ., Graduate School of Science, Assistant, 大学院・理学研究科, 助手 (60231263)
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| Co-Investigator(Kenkyū-buntansha) |
SETO Koji Shimane Univ., Fac. of Science and Technology, Assistant, 総合理工学部, 助手 (60252897)
TAKAHASHI Yoshio Hiroshima Univ., Graduate School of Scienc, Associate Prof., 大学院・理学研究科, 助教授 (10304396)
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| Project Period (FY) |
2000 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2001: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2000: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Keywords | tufas / carbonate / paleo-climate / stable isotopes / minor elements / シアノバクテリア / 炭酸塩堆積物 |
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| Research Abstract |
A tufa, a freshwater carbonate deposited in a limestone area, is an excellent tool for quantitative and highresolution analysis of terrestrial paleo-climate. Results of our investigation reveal that 1) laminated texture of tufas can be treated as annual layering developed due to seasonal change in precipitation rate of calcite. Estimation of microbial biomass shows that 2) the precipitation is not induced by photosynthesis of cyanobacteria living on the tufa surface. This and results of chemical analyses conduct to the conclusion that 3) equilibrium in terms of oxygen stable isotope and minor metal elements is confirmed in the calcite precipitation.
These contexts make paleo-climatic analyses using a laminated tufa possible, and the analyses were performed for the specimens collected from Shirokawa (Ehime Prefecture) and Niimi (Okayama Prefecture). We found that 4) oxygen isotopic composition changes very regularly together with annual layering. The change is reflected from regular seasonal change in water temperature. Furthermore, we realized that 5) rainfall events are recorded as brown-colored bands, which are rich in Si, and Al. Excellent correlation between positions of the bands and periods of the rainfall events was recognized.
This study provided new aspects of depositional processes and conditions of laminated tufas, and confirmed importance of the tufas in terms of paleo-climatological analytical tools
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