HR: 09:00h
AN: GP41B-05    [Abstracts]
TI: Age and Structure of the Laschamp Geomagnetic Excursion
AU: Scaillet, S
EM: scaillet@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91198 France
AU: * Laj, C
EM: laj@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91198 France
AU: Kissel, C
EM: kissel@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91198 France
AU: Guillou, H
EM: guillou@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91198 France
AU: Singer, B S
EM: bsinger@geology.wisc.edu
AF: University of Wisconsin, 1215 West Dayton Street , Madison, WI 53706 United States
AB: The age of the Laschamp geomagnetic excursion has been recently re-investigated using unspiked K/Ar and Ar/Ar techniques (Guillou et al., Session V01, this conference). The new age determination of 40.4 +/- 2.0 ka (2 sigma) is more precise than those previously reported in the literature and agrees precisely with that deduced from the GLOPIS-75 sedimentary paleointensity stack calibrated against the GISP2 ice core chronology. Two of the North Atlantic cores used in GLOPIS-75 (MD95-2034 and PS2644-5) yield rather detailed transitional VGP paths. In the two cases the paths show large similarities, with the VGP initially descending along mid-western Pacific, then returning to normal polarities with a large clockwise loop over Africa and Europe. Differences in the highest southern latitudes reached by the VGP can be explained assuming more different degrees of smearing of the paleomagnetic record due to differences in sedimentation rate in the two cores. In the most detailed record, MD95-2034 , two smaller loops are present preceding the main excursion. In the two cores, the excursion is characterized by a significant drop in intensity. The reversal paths observed for the Laschamp event are very close in position to those reported for the Icelandic Basin Event (IBE) from sites in the North Atlantic and the South China Sea (Laj et al., this conference) but differ in the sense of looping: while a clockwise loop is observed here, a counterclockwise loop is observed for the IBE. Despite this difference, the similarity of the transitional records tends to suggest that a similar, relatively simple, geometry has dominated the two excursions and therefore that similar dynamo mechanisms have prevailed during the reversal process.
DE: 1714 Geomagnetism and paleomagnetism
DE: 1035 Geochronology
DE: 1507 Core processes (8115)
DE: 1513 Geomagnetic excursions
DE: 1521 Paleointensity
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting