鹿児島市,花野火砕流の地磁気逆転エピソ-ドとこれによる上部第四系の編年

概要

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A reversed geomagnetic polarity episode in the late Brunhes epoch has been revealed in Keno- and Kogashira pyroclastic flow deposits distributed in Kagoshima City, South Kyushu, Japan. Considering the stratigraphic relations along with the fission track age determination, this episode could be correlated with the Blake polarity event. The virtual geomagnetic pole position of the Blake event can be estimated from the thermoremanent magnetization of this terrestrial pyroclastic flow deposits. The result supports the possible hypothesis of the centered dipole reversals of the Blake event, against the alternative hypothesis of the local reversal phenomena which were caused by a certain eccentric reversed dipole (DENHAM, 1976).Taking the Blake datum level in addition to radiometric age data as markers, a reliable chronostratigraphy is introduced. Such a chronostratigraphy is plausibly consistent with both the δ18O record of a Caribbean core P6304-9 and the most remarkable sea level changes known in South Kanto District, Japan. It is suggested that the late Pleistocene stratigraphic successions in this area were mostly controlled by the latest interglacial-glacial sea level changes (Fig. 4).