dorsal/arxiv
View SchemaRevisiting the Jurassic Geomagnetic Reversal recorded in the Lesotho Basalt (Southern Africa)
| Authors | Michel Prevot, Neil Roberts, John Thompson, Liliane Faynot, Mireille Perrin, Pierre Camps |
|---|---|
| Categories | |
| ArXiv ID | physics/0307015 |
| URL | https://arxiv.org/abs/physics/0307015 |
| DOI | 10.1046/j.1365-246X.2003.02029.x |
Abstract
We carried out a detailed and continuous paleomagnetic sampling of the reversed to normal geomagnetic transition recorded by some 60 consecutive flow units near the base of the Lesotho Basalt (183  1 Ma). After alternating field or thermal cleaning the directions of remanence are generally well clustered within flow units. In contrast, the thermal instability of the samples did not allow to obtain reliable paleointensity determinations. The geomagnetic transition is incompletely recorded due to a gap in volcanic activity attested both by eolian deposits and a large angular distance between the field directions of the flows underlying or overlying these deposits. The transition path is noticeably different from that reported in the pioneer work of van Zijl et al. (1962). The most transitional Virtual Geomagnetic Poles are observed after the volcanic hiatus. Once continents are replaced in their relative position 180 Ma ago, the post-hiatus VGP cluster over Russia. However, two successive rebounds from that cluster are found, with VGP reaching repeatedly Eastern Asia coast. Thus, the VGP path is not narrowly constrained in paleolongitude. The decrease in intensity of magnetization as the field deviates from the normal or reversed direction suggests that the decrease in field magnitude during the reversal reached 80-90%. We conclude that although the reversal is of a dipole of much weaker moment than that which existed on average during Cenozoic time, the characteristics of the reversing geodynamo seem to be basically similar.
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"abstract": "We carried out a detailed and continuous paleomagnetic sampling of the\nreversed to normal geomagnetic transition recorded by some 60 consecutive flow\nunits near the base of the Lesotho Basalt (183 \u0026#61617; 1 Ma). After\nalternating field or thermal cleaning the directions of remanence are generally\nwell clustered within flow units. In contrast, the thermal instability of the\nsamples did not allow to obtain reliable paleointensity determinations. The\ngeomagnetic transition is incompletely recorded due to a gap in volcanic\nactivity attested both by eolian deposits and a large angular distance between\nthe field directions of the flows underlying or overlying these deposits. The\ntransition path is noticeably different from that reported in the pioneer work\nof van Zijl et al. (1962). The most transitional Virtual Geomagnetic Poles are\nobserved after the volcanic hiatus. Once continents are replaced in their\nrelative position 180 Ma ago, the post-hiatus VGP cluster over Russia. However,\ntwo successive rebounds from that cluster are found, with VGP reaching\nrepeatedly Eastern Asia coast. Thus, the VGP path is not narrowly constrained\nin paleolongitude. The decrease in intensity of magnetization as the field\ndeviates from the normal or reversed direction suggests that the decrease in\nfield magnitude during the reversal reached 80-90%. We conclude that although\nthe reversal is of a dipole of much weaker moment than that which existed on\naverage during Cenozoic time, the characteristics of the reversing geodynamo\nseem to be basically similar.",
"arxiv_id": "physics/0307015",
"authors": [
"Michel Prevot",
"Neil Roberts",
"John Thompson",
"Liliane Faynot",
"Mireille Perrin",
"Pierre Camps"
],
"categories": [
"physics.geo-ph"
],
"doi": "10.1046/j.1365-246X.2003.02029.x",
"title": "Revisiting the Jurassic Geomagnetic Reversal recorded in the Lesotho Basalt (Southern Africa)",
"url": "https://arxiv.org/abs/physics/0307015"
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