オホーツク海完新世堆積物の岩石磁気学的研究 : 北海道網走沖北見大和堆周辺で採取された2本のコア試料

概要

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Marine sediment formed at a high sedimentation rate is distributed in the Okhotsk Sea, off Abashiri, Hokkaido. In order to make a detailed study of environmental changes in the area, we applied rock magnetic methods to two gravity cores covering 2, 700yrs (sediment rate about 150cm/yrs), GH00-1001 (water depth 461m) and GH00-1006 (water depth 1, 348m), recovered from the northern and southern basins near Kitamiyamato Bank. The dominant magnetic mineral in both cores is magnetite. A variety of rock magnetic parameters show three types of downcore variation, which are spiky anomalies suggesting the presence of volcanic ash and basaltic granules. Stepping down of the parameters indicates chemical change in a sedimentary environment, and the rather broad peaks suggest changes in the origin of detrital grains. Based on magnetic parameters, we also magnetically illustrated that increase in grain-size below -300cm (GH00-1001) and -150cm (GH00-1006) is a result of the dissolution of the fine part of magnetic grains in a reducing environment. Magnetic parameters are sensitive enough to pinpoint an episodic input of detrital material of different grain size and mineralogy at 275cm and 420cm (GH00-1001), which corresponds to the Kofun cold age (AD246-732).
日本第四紀学会の論文
2003-04-01