6:15 PM - 7:30 PM
[MIS24-P09] Sediment transportation changes based on spatiotemporal variations of Ni and Cr in the Hida range and off-Joetsu area.
Keywords:MD179 marine core, glacial-interglacial cycle, element analysis, Hime river, sediment transportation, summer monsoon
The samples were dried and powdered, and then pressed as tablets. Ni and Cr contents were measured by Wavelength Dispersive X-ray Spectrometry (Rigaku Primus II). Age models of 3296 and 3312 cores have been well-established by tephrochronology, radiometric dating, and oxygen isotope ratio of foraminifer (Nakamura et al., 2013; Takizawa et al., 2014, etc). Grain size of river bed sediments of Hime and Oumi river we analyzed by Laser diffraction particle size analyzer (Shimadzu SALD 3000S).
According to spatial distribution of Ni and Cr in geochemical map (Imai et al., 2010), clastic materials from Hime river appear to suspend and be transported by ocean current with gradually sinking within 20~30km from Hime river mouth, and farther than 20~30km, clastic materials appear to flow down by sediment gravity flow. Grain size analysis of river bed sediments of Hime and Oumi river indicates that Ni and Cr are included mainly in coarse grain, and suggests that Ni and Cr are mineral state. Ni and Cr show high concentration near the ultramafic rock, and it is suggested that origin of Ni and Cr is especially restricted in specific parts of Hime and Oumi rivers. Hime and Oumi rivers are steep and have extremely narrow continental shelf around their river mouths, and their source is the northern part of Hida range.
Concentration of Ni and Cr in 3296 and 3312 cores are very similar to each other, and tend to be high (low) during interglacial (glacial) age. However, peaks of Ni and Cr concentration in 3296 core are higher than the other cores. Ni and Cr content rate of RC1408 core is half or one third of 3296 core. Temporal changes of Ni and Cr shows close relation with temperature or rainfall of the Japan Alps estimated from total organic carbon proxy of sediments at the bottom of some lakes (Kumon et al., 2009). Considering topographical steep condition of Hime river, main factor to change concentration of Ni and Cr appear to be changing supply of the serpentine because of changing rainfall influenced by summer monsoon.
This research was a part of METI's project entitled "FY2014 Promoting research and development on methane hydrate".
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Nakamura et al. (2013) Jour. Japan. Assoc. Pet. Technol., 78, 79-91.