福島県小高町の上部更新統中の地球磁場逆転について

概要

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Paleomagnetic study was made on the Late Pleistocene Tsukabara Formation developed along the Pacific coast of Fukushima Prefecture, Northeast Honshû, Japan. The Tsukabara is the marine terrace formation which is considered to have been deposited in the Last Interglacial stage and consists of the lower gravels, the middle silts, and the upper gravels.The remanent magnetization was measured on approximately 100 oriented samples cored at about 20cm interval over the middle part of the formation at its type-locailty (37°35′N, 141°02′E). The intensity of the remanent magnetization of the sediment samples after demagnetization in the alternating magnetic field of 100 Oe ranged from 10-5 to 10-7emu/cm3.As the result of paleomagnetic analysis four horizons of polarity transition were recognized. The changes in inclination were generally associated with those in declination. Referring to the geological and biostratigraphical evidences, these reversed polarity intervals are judged to be equivalent to the Blake event (108, 000-114, 000 y.B.P.) in the Brunhes Normal Polarity Epoch, which was first reported by Smith and Foster (1969) from the North Atlantic deep-sea cores. The present result suggests a split nature of the Blake event.
日本第四紀学会の論文