Paleomagnetic records of excursions and reversals: possible biases caused by magnetization artefacts

• Published in: Physics of the Earth and Planetary Interiors
• Main Authors: Quidelleur, Xavier, Valet, Jean-Pierre
• Other Authors: Institut de Physique du Globe de Paris (IPG Paris)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 1994
• Subjects: [SDU]Sciences of the Universe [physics]; Geomagnetic Pole
• Online Access: https://hal.science/hal-03991335; https://doi.org/10.1016/0031-9201(94)90100-7

Sedimentary and volcanic records of the Mono Lake (27 ka), Laschamp (42 ka), Blake (128 ka) and Cobb Mountain (1.1 Ma) geomagnetic excursions/events have been selected to test the coherency of the records and the hypothesis of preferred longitudes followed by the virtual geomagnetic pole (VGP) during transitional periods. The distribution of the mean VGP longitudes (MVLs) for each individual event is not consistent with any simple pattern. The entire data set, including a total of six excursions, shows no preference for longitudinal sectors. The databases, one including both reversal and excursion records and another which contains only reversals, show that most of the MVLs with low dispersion values are at 90° from their site longitudes, with the majority lying over two preferred antipodal sectors of longitude. The other MVLs (with high dispersion values) are distributed in longitude around the globe. These two databases also show that the MVLs which do not lie at 90° from the site longitude are scattered around the globe, whereas the others are confined within two preferential bands of longitude. It is thus suggested that observations of two preferred sectors of longitude are the consequence of artefacts possibly linked to the acquisition of magnetization in sediments. We show that a shallowing of inclinations close to the horizontal plane, induced by the dominance of gravity forces in the presence of a very weak field, is compatible with these observations.