鬼界アカホヤテフラと福井県勝山市の池ケ原堆積物の古地磁気研究

概要

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Paleomagnetic measurements were made on the Kikai-Akahoya tephra（K-Ah）and the Ikegahara sediment（IK）of the Katsuyama Area, Fukui Prefecture. The stable component of remanent magnetizationwas isolated from the samples at 5 sites of K-Ah and at 12 horizons of IK through stepwise alternating fielddemagnetization up to 30 mT.The site-mean directions of K-Ah are almost identical with one another. Magnetic minerals in the K-Ahsamples are chiefly titanomagnetite or magnetite, which are considered to be not secondary minerals, basedon experimental results of stepwise IRM acquisition and thermal demagnetization of a three-componentIRM. These facts indicate that their magnetic directions were acquired under the geomagnetic field at theeruption time of K-Ah.Horizon-mean magnetic directions from IK continuously change against depth with amplitude of about15°. The change likely originated from ancient geomagnetic secular variation.The paleomagnetic direction of the uppermost horizon of IK, which contains volcanic glass shards derivedfrom K-Ah, is consistent with the directions obtained from K-Ah. This suggests that the formation ofthe horizon was nearly simultaneous with the eruption of K-Ah.
福井大学の論文