Longitudinal confinement of geomagnetic reversal paths as a possible sedimentary artefact

Langereis, Cor G.; Hoof, A.A.M. van; Rochette, P.

doi:10.1038/358226a0

Cited by 109 publications

(69 citation statements)

References 35 publications

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“…Criticism was expressed, however, concerning the reliability of sedimentary VGP paths. Smoothing due to the remanence acquisition process could produce a ficticious longitudinal confinement [Langereis et al, 1992]. Rapid VGP movements and the possibly long-lived VGP clusters [Hoffman, 1996] could be obscured by the smoothing.…”

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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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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“…The smoothing may well be due to the filtering mechanism of remanence acquisition in these sediments. The coincidence of the transitional data and the smoothed non-transitional directions is also apparent in several other transitional records from the Sicilian Trubi marls [6]. This strongly indicates that the filtering mechanism of the acquisition of the sediment obscures the real geomagnetic transitional directions.…”

Section: The Sicilian Lower and Upper Tht~era Recordsmentioning

confidence: 73%

“…However, Rochette [4] showed that smoothing of the non-antipodal directions before and after a transition will also result in VGP paths with a strong longitudinal confinement. By smoothing the mean stable directions before and after late Miocene and Pliocene transitions sampled in the Mediterranean, Langereis et al [6] found synthetic VGP paths confined to the Americas which were identical to the observed VGP paths.…”

Section: The Sicilian Lower and Upper Tht~era Recordsmentioning

confidence: 99%

“…Mary and Courtillot [10] found that, in many reversals, the reversing fields decrease and subsequently increase along the dipole direction on which a random noise is superposed. In addition, Langereis et al [6] have shown that the longitudinal confinement of the VGP paths from sedimentary records can also be explained by a process of smoothing of the stable non-antipodal directions before and after the transitions. Clearly, many more transitional records from both lavas and sediments are required before there is a consensus on this matter.…”

Section: Introductionmentioning

confidence: 99%

“…Detailed records of geomagnetic transitions have been obtained from different sources, the most important of which are those recorded in lava sequences and those in sedimentary sequences. Although sedimentary sequences concern appropriate time control and continuous registration of the geomagnetic signal, the recording mechanism in sediments is still badly understood and may easily lead to sedimentary arte- facts [3][4][5][6]. However, Laj et al [7] and Tric et al [8] concluded, from studies of the VGP paths of several transitions (showing a wide distribution in both time and place) that the VGP paths are predominantly confined to a longitudinal band over the Americas or its antipode, and that there may have been a strong dipolar field during transitions.…”

Section: Introductionmentioning

confidence: 99%

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The upper and lower Thvera sedimentary geomagnetic reversal records from southern Sicily

Hoof¹,

Langereis²

1992

Earth and Planetary Science Letters

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Detailed paleomagnetic records of the upper and lower Thvera polarity transitions have been determined from Pliocenc marine marls in southern Sicily. The dominant magnetic mineral is fine grained magnetite. The two transitions have VGP paths following a great circle passing South America and the west coast of North America. There are strong indications that the VGP paths result from smoothing of the non-antipodal stable directions before and after the transitions. The upper Thvera transitional record is preceded by two excursions and followed by a third one. The first excursion is a sedimentary artefact caused by post-depositional migration of magnetic minerals and the third one by is caused by weathering of the sediment. The upper Thvera transition from Sicily is compared with the record from Calabria, about 250 km away. The two records show similarities as well as differences: both transitions have identical VGP paths, but in Calabria the transition is recorded lower in the sediment, the first and third excursions have different characters and the second one is not present. Apparently the registration of transitions of the Earth's magnetic field in sediments is strongly influenced by smoothing and diagenetic processes after deposition.

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Deciphering records of geomagnetic reversals

Valet

Fournier

2016

Rev. Geophys.

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Polarity reversals of the geomagnetic field are a major feature of the Earth's dynamo. Questions remain regarding the dynamical processes that give rise to reversals and the properties of the geomagnetic field during a polarity transition. A large number of paleomagnetic reversal records have been acquired during the past 50 years in order to better constrain the structure and geometry of the transitional field. In addition, over the past two decades, numerical dynamo simulations have also provided insights into the reversal mechanism. Yet despite the large paleomagnetic database, controversial interpretations of records of the transitional field persist; they result from two characteristics inherent to all reversals, both of which are detrimental to an ambiguous analysis. On the one hand, the reversal process is rapid and requires adequate temporal resolution. On the other hand, weak field intensities during a reversal can affect the fidelity of magnetic recording in sedimentary records. This paper is aimed at reviewing critically the main reversal features derived from paleomagnetic records and at analyzing some of these features in light of numerical simulations. We discuss in detail the fidelity of the signal extracted from paleomagnetic records and pay special attention to their resolution with respect to the timing and mechanisms involved in the magnetization process. Records from marine sediments dominate the database. They give rise to transitional field models that often lead to overinterpret the data. Consequently, we attempt to separate robust results (and their subsequent interpretations) from those that do not stand on a strong observational footing. Finally, we discuss new avenues that should favor progress to better characterize and understand transitional field behavior.

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Longitudinal confinement of geomagnetic reversal paths as a possible sedimentary artefact

Cited by 109 publications

References 35 publications

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

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

The upper and lower Thvera sedimentary geomagnetic reversal records from southern Sicily

Deciphering records of geomagnetic reversals

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