| Budget Amount *help |
¥3,670,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥270,000)
Fiscal Year 2007: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2006: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
The anisotropy of magnetic susceptibility (AMS) of sand-sized sediments has been believed to indicate the preferred grain orientation of the sediments. No study, however, has been verified this assumption. This project aimed to examine what generate the AMS of sand-sized sediments, using X-ray CT method and the fabric map method.
At first, grain fabric of parallel-lamination is examined by three methods mentioned above. At the same time, we examined the effect of bed-aggradation rate on the formation and grain fabric of parallel-lamination. A new method, density-based cluster analysis that deal with the dominant combinations of shapes and orientation of grains, was developed to analyze the X-ray CT data. It is revealed that the bed-aggradation rate effects on the features of the parallel-laminations and the combination of the shapes and orientation of the grains. In addition, averaged angles of grain imblication obtained from the three methods agreed within their error ranges.
Next, we examined the mineral and chemical compositions and the magnetic features of the "Toyoura quartz sand", which is commonly used for the flume experiments; to determine the mineral that contribute the AMS. As the results, it is revealed that the "Toyoura quartz sand" consists of quartz, plagioclase, potassium feldspar, amphibole, garnet, rutile, biotite, ilmenite, and magnetite. Ilmenite grains mainly contribute the magnetic susceptibility in this material. Magnetic minerals and non-magnetic minerals were divided by the CT values which correspond to the theoretical values of X-ray linear attenuation coefficient for each mineral. The results obtained by three methods for settling experiments showed that AMS showed the preferred grain orientations of magnetic minerals rather than bulk sediments. Samples those of grain flow experiments show different distribution for the three methods. More analyses such as for wider range of X-ray CT data will be needed to solve the problem.
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