Geomagnetic polarity epochs: Sierra Nevada II

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Ten new determinations on volcanic extrusions in the Sierra Nevada with potassium-argon ages of 3.1 million years or less indicate that the remanent magnetizations fall into two groups, a normal group in which the remanent magnetization is directed downward and to the north, and a reversed group magnetized up and to the south. Thermomagnetic experiments and mineralogic studies fail to provide an explanation of the opposing polarities in terms of mineralogic control, but rather suggest that the remanent magnetization reflects reversals of the main dipole field of the earth. All available radiometric ages are consistent with this field-reversal hypothesis and indicate that the present normal polarity epoch (N1) as well as the previous reversed epoch (R1) are 0.9 to 1.0 million years long, whereas the previous normal epoch (N2) was at least 25 percent longer.
Publication type Article
Publication Subtype Journal Article
Title Geomagnetic polarity epochs: Sierra Nevada II
Series title Science
Volume 142
Issue 3590
Year Published 1963
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Science
First page 382
Last page 385
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