Origin and age of the directions recorded during the Laschamp event in the Chaîne des Puys (France)

Plenier, Guillaume; Valet, Jean‐Pierre; Guérin, Gilles; Lefèvre, Jean‐Claude; LeGoff, Maxime; Carter-Stiglitz, Brian

doi:10.1016/j.epsl.2007.04.039

Cited by 43 publications

(39 citation statements)

References 52 publications

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“…However, despite these recent advances, the database for records of excursions remains much smaller than for reversals. The Laschamp event (Bonhommet, 1970) is the best documented episode with very recent detailed sedimentary records (Lund et al, 2005;Laj et al, 2006) from various locations ( Figure 1c) and several volcanic data that we have summarized in Figure 1d (Chauvin et al, 1989;Plenier et al, 2007). It is interesting that, similarly to reversals, volcanic VGPs appear to be rather scattered.…”

Section: Introductionmentioning

confidence: 92%

Simulations of a time-varying non-dipole field during geomagnetic reversals and excursions

Valet¹,

Plenier²

2008

Physics of the Earth and Planetary Interiors

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Reversals and excursions have been simulated by decreasing the axial dipole field to zero while leaving up a time-varying non-dipolar field similar to the CAL7K model (Korte and Constable, 2005). We also envisaged the situation in which the total field changes sign. We first investigated the relationship between the non-axial dipole structure of the historical and present field snapshots and the virtual geomagnetic poles ( Smearing of the signal by sedimentary records considerably amplifies the longitudinal confinment of the VGPs. Overall, these simulations account for most characteristics reported in detailed reversal records, and thus strongly support the concept of a non-dipolar transitional field. We also simulated field excursions by assuming either a vanishing dipole followed by its return to initial polarity or by a short episode with the opposite polarity preceding its restoration. The model accounts for the different characteristics inherent to the volcanic and sedimentary records of the recent excursions. The simple structure of sedimentary VGP paths dominated by a large loop between northern and southern latitudes partly results from smearing of the signal. Therefore, these records do not fully describe the complexity of the excursional field and remain exclusively sensitive to very low degree harmonics. Most detailed studies of excursions exhibit reversed directions which cannot exist without a very short dipolar episode of opposite polarity.

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Section: Introductionmentioning

confidence: 92%

Simulations of a time-varying non-dipole field during geomagnetic reversals and excursions

Valet¹,

Plenier²

2008

Physics of the Earth and Planetary Interiors

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“…VGP paths (colour coded according to the site label for each respective sediment core with the overall pattern summarized by the orange loops) for the (a) Laschamp and (b) Iceland Basin excursions (from Laj et al [2006]). Volcanic VGPs are shown for comparison for the Laschamp excursion at Laschamp‐Olby (red cluster) [ Guillou et al , 2004], Olby (dark blue), Royat (yellow), Louchadière (purple) [ Plenier et al , 2007], and McLennan Hills, Auckland volcanic field, New Zealand (light blue) [ Mochizuki et al , 2006], which is Auckland cluster 2 of Cassata et al [2008].…”

Section: Key Questions In Geomagnetic Excursion Research: Knowns and mentioning

confidence: 99%

Geomagnetic excursions: Knowns and unknowns

Roberts

2008

Geophysical Research Letters

167

152

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[1] Geomagnetic excursions are short-lived episodes when Earth's magnetic field deviates into an intermediate polarity state. Understanding the origin, frequency, amplitude, duration, and field behavior associated with excursions is a forefront research area within solid earth geophysics. Recent advances in excursion research are summarized here, and key further research is suggested to resolve major unanswered questions. Improving the global distribution of excursion records, particularly from the southern hemisphere, obtaining high-resolution sedimentary excursion records with good age control from sites with sedimentation rates >10 cm/kyr, obtaining volcanic excursion records coupled with high-precision geochronology, and estimating excursion duration with high chronological precision will all facilitate hypothesis testing concerning the deep earth dynamics that generate geomagnetic excursions.

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“…The first dating by Bonhommet and Zahringer [1969] using K/Ar methods performed on whole rock led to an age determination between 8 and 20 ka. After almost four decades of geochronologic investigations using K–Ar, thermoluminescence, 40 Ar/ 39 Ar and 230 Th– 238 U methods [e.g., Bonhommet and Zahringer , 1969; Condomines , 1980; Hall and York , 1978; Gillot et al , 1979; Chauvin et al , 1989; Plenier et al , 2007], the most reliable radiometric age data sets finally led to concordant ages of 40.4 ± 2.0 ka [ Guillou et al , 2004] and 40.7 ± 1.0 ka BP [ Singer et al , 2009]. Meanwhile, the Laschamp excursion has been identified worldwide as a large amplitude swing of the magnetization vectors, and/or as a dramatic paleointensity low in lava flows [e.g., Kristjansson and Gudmundsson , 1980; Roperch et al , 1988; Levi et al , 1990; Mochizuki et al , 2006; Cassata et al , 2008] and sediments [e.g., Thouveny and Creer , 1992; Vlag et al , 1996; Lund et al , 2005; Channell , 2006; Thouveny et al , 2004].…”

Section: Introductionmentioning

confidence: 99%

Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric ¹⁰Be overproduction: Contribution of authigenic ¹⁰Be/⁹Be ratios in west equatorial Pacific sediments

Ménabréaz¹,

Bourlès²,

Thouveny³

2012

J. Geophys. Res.

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Authigenic 10Be/9Be ratios were measured along a sediment core collected in the west equatorial Pacific in order to reconstruct cosmogenic 10Be production variations near the equator, where the geomagnetic modulation is maximum. From 60 to 20 ka, the single significant 10Be production impulse recorded at 41 ka results from the geomagnetic dipole low that triggered the Laschamp excursion. No significant 10Be overproduction signature is recorded at the age of the Mono Lake excursion (∼34 ka). A compilation of authigenic 10Be/9Be records obtained from sediments was averaged over a 1 kyr window and compared with the 1 kyr averaged 10Be flux record of Greenland ice cores. Their remarkable similarity demonstrates that 10Be production is globally modulated by geomagnetic dipole variations and redistributed by atmosphere dynamics. After calibration using absolute values of the virtual dipole moment drawn from paleomagnetic database, the authigenic 10Be/9Be stack allows reconstructing the geomagnetic dipole moment variations over the 20–50 ka time interval. Between 48 and 41 ka, the dipole moment collapsed at a rate of −1.5 × 1022 A m2 kyr−1, which will be an interesting criterion for the assessment of the loss rate of the historical field and the comparison of dipole moment loss prior to excursions and reversals. After a 2 kyr duration of the minimum dipole moment (∼1 × 1022 A m2), a slow increase started at 39 ka, progressively reaching 5 × 1022 A m2 at 20 ka. The absence of a significant dipole moment drop at 34 ka, the age of the Mono lake excursion, suggests that the duration and amplitude of the dipole weakening cannot be compared with that of the Laschamp. This study provides a reliable basis to model the production of radiocarbon and in situ cosmogenic nuclides and to improve the calibration of these dating methods.

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Origin and age of the directions recorded during the Laschamp event in the Chaîne des Puys (France)

Cited by 43 publications

References 52 publications

Simulations of a time-varying non-dipole field during geomagnetic reversals and excursions

Simulations of a time-varying non-dipole field during geomagnetic reversals and excursions

Geomagnetic excursions: Knowns and unknowns

Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric ¹⁰Be overproduction: Contribution of authigenic ¹⁰Be/⁹Be ratios in west equatorial Pacific sediments

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Origin and age of the directions recorded during the Laschamp event in the Chaîne des Puys (France)

Cited by 43 publications

References 52 publications

Simulations of a time-varying non-dipole field during geomagnetic reversals and excursions

Simulations of a time-varying non-dipole field during geomagnetic reversals and excursions

Geomagnetic excursions: Knowns and unknowns

Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric 10Be overproduction: Contribution of authigenic 10Be/9Be ratios in west equatorial Pacific sediments

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Product

Resources

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Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric ¹⁰Be overproduction: Contribution of authigenic ¹⁰Be/⁹Be ratios in west equatorial Pacific sediments