HR: 1340h
AN: GP43B-0857    [Abstracts]
TI: Short wavelength magnetic anomalies in the Indian and Pacific Oceans after the Cretaceous Normal Superchron (40-83 Ma).
AU: * Bouligand, C
EM: bouligan@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: Dyment, J
EM: jdy@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: Gallet, Y
EM: gallet@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: Hulot, G
EM: gh@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AB: Temporal variations of the magnetic field of the Earth span a large spectrum of timescales : from year to hundred of millions of years (from secular variation to variations of the magnetic reversals frequency). Many questions remain unsolved, particularly about the long term evolution of the intensity of the magnetic field and about a possible link between secular variation and the magnetic reversals frequency. Study of marine magnetic measurements may complement measurements of the remanent magnetisation acquired on volcanic rocks or sediments in order to recover the long term evolution of the intensity of the magnetic field. Indeed, the magmatic oceanic crust is a good recorder of the magnetic reversals but also of the variations of the intensity of the magnetic field. The goal of this study is to use marine magnetic anomaly profiles to estimate fluctuations of the magnetic field for a period when the reversal rate was low (40-83 Ma) and to compare it with the last millions of years which are characterised by a high reversals frequency. Many sea-surface magnetic profiles are available. Magnetic anomalies are of two origins : the variations of the magnetic field during the cooling of the oceanic crust and local effects due to the structure of the lithosphere. In order to discriminate between the paleovariations of the magnetic field (the signal) and the local effects (the noise), the study deals with different regions of the Earth. The Indian and Pacific Oceans exhibit fast spreading rates during the period investigated and insure better resolution. In each study area, selected profiles are reduced to the pole, stretched with the help of the main magnetic anomalies (due to reversals) and stacked in order to increase the signal to noise ratio. Preliminary results reveals systematic micro-anomalies which correspond to variations of the magnetic dipole intensity or short polarity intervals. Over the 40 Ma period investigated, we observed the same micro-anomalies than Cande and Kent(1992) (between 53 and 61 Ma) but also many additional micro-anomalies in other chrons. The number of observed micro-anomalies observed is heavily dependent on the spreading rate. Cande, S.C., and D.V. Kent, Ultrahigh resolution marine magnetic anomaly profiles: A record of continuous paleointensity variations?, J. Geophys. Res., 97, 15075-15083, 1992.
DE: 3005 Geomagnetism (1550)
DE: 1513 Geomagnetic excursions
DE: 1521 Paleointensity
DE: 1522 Paleomagnetic secular variation
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting