Letter | Published:

K–Ar and 40Ar/39Ar Age of the Laschamp geomagnetic polarity reversal

Naturevolume 274pages462464 (1978) | Download Citation



THE Laschamp polarity reversal1 remains one of the best documented cases of a recent excursion of the Earth's magnetic field. Unlike lake sediments, the Laschamp volcanics have a stable TRM (thermo remanent magnetism) which is not susceptible to structural degradation or detrital inclination error. Some workers have claimed to have seen the Laschamp excursion in recent sediments2, while others have been unable to establish a correlation between the Laschamp and sedimentary core samples3,4. One of the main difficulties with such a correlation is the uncertainty in the age of the Laschamp and Olby lava flows which record the excursion. We have performed a new series of K–Ar and 40Ar/39Ar analyses which suggest that the Laschamp excursion is significantly older than the widely quoted age reported by Bonhommet and Zähringer1.

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  1. 1

    Bonhommet, N. & Zähringer, J. Earth planet. Sci. Lett. 6, 43–46 (1969).

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    Noel, M. & Tarling, D. H. Nature 253, 705–707 (1975).

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    Denham, C. R. & Cox, A. Earth planet. Sci. Lett. 13, 181–190 (1971).

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    Thompson, R. & Berglund, B. Nature 263, 490–491 (1976).

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    Hall, C. M. & York, D. Eos 59, 388–389 (1978).

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    Yaskawa, K. et al. J. Geomag. Geoelec. 25, 447–474 (1973).

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  1. Geophysics Division, Department of Physics, University of Toronto, Toronto, Ontario, Canada, M5S 1A7

    •  & DEREK YORK


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