隠岐および見島の鮮新世～更新世火山岩の古地磁気学的研究

その他

In recent years many workers have a great store of the information on reversals of the geomagnetic field during the late Tertiary. The age or the time interval of the field reversal in the late Pliocene and the early Pleistocene are minutely obtained by using the radiometrically dated rocks (Cox et al, 1963, 1964 ; Gromme and Hay, 1963 ; McDougall and Tarling, 1963). According to these results, it seems that the change of the geomagnetic field direction from the normal to the reverse or in the opposed way abruptly took place and a transition occurred in a short interval of time. On the other hand, one of the present authors reported that there exists the positional intermixing of the normal and the reverse magnetization in the same lava (Asami, 1954, 1956). This fact strongly suggests that the natural remanent magnetization (NRM) in some rocks was acquired by a self-reversing process of ferromagnetic minerals in the rock during or after the formation.
For the purpose of clarifying these two questions, the present authors searched localities containing both lavas of the normal and the reverse NRM and carried out their palaeomagnetic researches.