Polarity excursion
A pole excursion or geomagnetic excursion is a significant change in the prevailing geometry of the earth's magnetic field over a few 100 to a few 1000 years. Often the dipole component becomes weak, anomalies relatively stronger, or the field remains strong when the magnetic poles are shifted by 10 to 20 °. The polarity is the same before and after an excursion, which is why these relatively short events are not easily visible in time series of remanent magnetization of sedimentary rocks .
If, on the other hand, the field builds up again with the opposite polarity, which takes only a little longer overall, there is a clearly visible pole shift . Pole shifts limit the chrons and subchrons of magnetostratigraphy . They are comparatively rare: seven excursions have been known since the last pole shift 780,000 years ago, proven also by increased concentrations of beryllium -10 in the sediment. This isotope is created in the high atmosphere ; amplified when the magnetic field is weak.
Well-known and dated polarity excursions are the Laschamp event and the Mono Lake excursion .
Individual evidence
- ^ Palaeomagnetism and Rock Magnetism Research Group, Univ. Oxford: Geomagnetic Excursions ( Memento of the original from March 5, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . Retrieved April 22, 2015.
