Geographical distribution of transitional VGPs: Evidence for non-zonal equatorial symmetry during the Matuyama-Brunhes geomagnetic reversal

Clement, Bradford M.

doi:10.1016/0012-821x(91)90236-b

Cited by 190 publications

(128 citation statements)

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“…In common with other records, a number of the VGP paths in this study show preferred longitude bands, but these bands are not consistent within this study and are not all consistent with other studies (VALET et al, 1988;CLEMENT, 1991). Furthermore, although stages b to e have VGP paths which fall partly within the antipodal preferred bands of LAJ et al (1991), the VGP path of the final stage falls within a well defined longitude band which is midway between the two preferred bands and is also clearly not axisymmetric.…”

Section: Comparison With Other M/b Records and The Geometry Of The Trcontrasting

confidence: 83%

“…Furthermore, although stages b to e have VGP paths which fall partly within the antipodal preferred bands of LAJ et al (1991), the VGP path of the final stage falls within a well defined longitude band which is midway between the two preferred bands and is also clearly not axisymmetric. This indicates that the reversal cannot be adequately explained either by the models invoking preferred longitudinal bands over the Americas and their antipode (TRIG et al, 1991;LAJ et al, 1991;CLEMENT, 1991) or by models in which the transitional field is dominated by time-dependent low order zonal harmonics (HOFFMAN and FULLER, 1978;WILLIAMS and FULLER, 1981). In common with the conclusions of VALET et al (1992), we find evidence in our record which supports the presence of drifting non-dipole sources, these giving rise to a number of loops in the VGP paths, features which are also present in a loess record of the Lower Jaramillo R-N transition (ROLPH, 1993).…”

Section: Comparison With Other M/b Records and The Geometry Of The Trmentioning

confidence: 99%

“…Subsequently, a transition model was proposed based on the hypothesis that the most important harmonic components of the transitional geomagnetic field are the low order zonal terms (HOFFMAN and FULLER, 1978). However, the hypothesis of axisymmetric fields during the transitional period has been questioned by the discovery of transition records exhibiting VGP paths which are not clearly near-or far-sided (VALET et al, 1989;CLEMENT, 1991). Although recent data from both the northern and southern hemisphere suggest that the M/B transitional field displays equatorial symmetry (CLEMENT, 1991), we still can not make reliable conclusions about the morphology of the geomagnetic field during the reversal.…”

Section: Introductionmentioning

confidence: 99%

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Matuyama/Brunhes (M/B) Transition Recorded in Chinese Loess.

Donghuai¹,

Shaw²,

An³

et al. 1993

J. geomagn. geoelec

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Here we present a detailed record of the Matuyama/Brunhes (M/B) polarity transition recorded in a loess section at Xifeng (36°N, 108°E), in the central part of the Chinese loess plateau. The transition zone, which occurs in loess unit L8, has a thickness of 3.8 m and was sampled in full. At this point in the section the loess accumulation rate has been estimated at 10 cm/ka, and with the size of sub-sample used provides a potential time resolution of 240 years. Magnetite has been identified as the main magnetic mineral with a small contribution from maghaemite or cation deficient magnetite. The remanence of all samples was investigated using thermal demagnetisation from room temperature up to 650°C. The results indicate a duration of 32,000 years for the decay and recovery of the main dipole intensity, and 20,000 years for the period of maj or directional change. During the transition the field intensity falls to an average of 30% of its value before and after the transition, although there are strong variations about this weak value which accompany a sequence of 4 reversed/normal/reversed fluctuations of the local field vector. These fluctuations immediately preceed the final reversed-normal transition, after which the field intensity recovers to its pre-transition value. Calculated VGP paths of most stages are continuous and confined to preferred longitude bands which include America, the Atlantic Ocean or Africa. Field behaviour during the transition period suggests that non-dipolar terms are dominant while the dipole field is weak, with the dipole decay and recovery associated with the increased influence of low order zonal terms of the geomagnetic field.

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Section: Comparison With Other M/b Records and The Geometry Of The Trcontrasting

confidence: 83%

Section: Comparison With Other M/b Records and The Geometry Of The Trmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Matuyama/Brunhes (M/B) Transition Recorded in Chinese Loess.

Donghuai¹,

Shaw²,

An³

et al. 1993

J. geomagn. geoelec

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“…From a compilation of sedimentary data, Clement [1991] and Laj et al [1991] found that virtual geomagnetic poles (VGPs) exhibit a longitudinal preference for two separate paths during reversals: one along the Americas and the other along an East Asian longitudinal track. This observation was not confirmed by a compilation of $400 intermediate poles from volcanic records [Prévot and Camps, 1993].…”

Section: Introductionmentioning

confidence: 99%

A reversal of the Earth's magnetic field recorded in mid‐Miocene lava flows of Gran Canaria: Paleodirections

et al. 2002

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[1] A paleomagnetic investigation has been carried out on a continuous series of 87 volcanic lava flows from the mid-Miocene shield basalts of Gran Canaria. The sequence covers a reversal of the Earth's magnetic field from reverse to normal. Intermediate directions of the field are recorded in 34 lava flows. During the reversal the virtual geomagnetic poles (VGPs) show an accumulation in three consecutive areas: southeast of South America, east of India, and in the central Pacific. In addition to the reversal three excursions are recorded in the sequence, two preceding and one succeeding the reversal. The intermediate directions of the excursion just before and after the transition have the same VGP positions as the first and the last accumulation zone, respectively. From radiometric age constraints this transition corresponds very likely to a $14.1 Ma field reversal. The remarkable returns to the same transitional positions near South America and the central Pacific indicate preferred locations of the VGP during the transitional stages. Only the South America cluster can be correlated to VGP clusters observed in other reversals of the last 10 Myr and to lower mantle seismic anomalies. The VGPs in the Pacific track instead along the antipode of the site longitude. This indicates that mechanisms other than lower mantle heterogeneities additionally affect the transitional record of the sampled sequence and zonal harmonics are plausible candidates.

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“…Initially, it was not realized that excursions might have a different nature than reversals, so the VGP paths obtained for the most detailed ones have been considered together with reversal paths, when statistically testing the hypothesis of preferential bands for transitional VGP paths (Laj et al, 1991;Clement et al, 1991;McFadden et al, 1993). More recently, however, processes related to the Earth's inner core were suggested which distinguish between reversals and excursions.…”

Section: Page 3 Of 29mentioning

confidence: 99%

Morphology of the Iceland Basin Excursion from a spherical harmonics analysis and an iterative Bayesian inversion procedure of sedimentary records

Lanci

Kissel

Leonhardt

et al. 2008

Physics of the Earth and Planetary Interiors

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Pacific. For these reasons, our modeling results should only be regarded as preliminary models of the geomagnetic field during the IBE, susceptible to improvements when including results from future paleomagnetic studies. Nevertheless, both approaches show distinct similarities and are stable against moderate variations of modeling parameters. The general picture is that of a dipole field undergoing a strong reduction, but remaining higher than the non-dipole field all through the excursional process, except for a very short interval of time corresponding to the dipole minimum at the center of the excursion. On the other hand, some differences exist between the results of the two models with each other and with the real data when the virtual geomagnetic pole (VGP) paths are considered. The non-dipole field does not appear to undergo very significant changes during the excursion except for a slight increase just at the dipole minimum. The width of mid- * ManuscriptPage 2 of 29 A c c e p t e d M a n u s c r i p t -2-height of the dipole minimum, which can be considered as an approximate measure of the duration of the IBE is of the order of 3kyr according to the SPECMAP age model, consistent with a suggestion by Gubbins (1999). These results are compared to those obtained for the MatuyamaBrunhes geomagnetic reversal .

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Geographical distribution of transitional VGPs: Evidence for non-zonal equatorial symmetry during the Matuyama-Brunhes geomagnetic reversal

Cited by 190 publications

References 29 publications

Matuyama/Brunhes (M/B) Transition Recorded in Chinese Loess.

Matuyama/Brunhes (M/B) Transition Recorded in Chinese Loess.

A reversal of the Earth's magnetic field recorded in mid‐Miocene lava flows of Gran Canaria: Paleodirections

Morphology of the Iceland Basin Excursion from a spherical harmonics analysis and an iterative Bayesian inversion procedure of sedimentary records

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