地磁気の逆転とエクスカーション

概要

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A geomagnetic reversal times cale is useful for determining the age of a sequence of rocks. It must be stressed, however, that a magnetostratigraphic sequence by itself does not provide unequivocal dates for geological events preserved in rocks, since magnetic reversals are repetitive events and do not in general possess singular properties. Independent criteria, such as paleontologic or radiometric data, are thus required to verify the age of a sequence. In this paper the magnetostratigraphy of Miocene rocks in Kenya is described as a typical example of magnetic dating. The polarity sequence is correlated to the geomagnetic reversal time scale by HARLAND et al. (1982) on the basis of the K-Ar ages and stratigraphic relation. Some short polarity events and excursions with in the Brunhes normal polarity epoch were discovered from Lake Biwa core. They offer the potential of providing very sharp stratigraphic markers. Many other paleomagnetic results on short events and excursions are also summarized in this paper. Four postulated short events with in the Brunhes normal epoch can be traced globally, and can be useful for stratigraphic markers. These are the Blake, Biwa I, Biwa II and Emperor events, which occurred at about 0.11, 0.18, 0.28 and 0.47 Ma. However, excursions have proven disappointingly difficult to trace globally. Excursions are probably local rather than global geomagnetic phenomena.
日本地質学会の論文
1988-02-25