The upper and lower Nunivak sedimentary geomagnetic transitional records from southern Sicily

Hoof, A.A.M. van; Os, Bertil van; Langereis, C.G.

doi:10.1016/0031-9201(93)90105-i

Cited by 11 publications

(2 citation statements)

References 27 publications

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“…The VGP paths from these records are similar to several others in that the VGPs persist over South America for approximately 2000-3000 yr. Although Van Hoof et al [41] noted the probability that the Sicilian records had been heavily smoothed, they pointed out that the records are still consistent with Hoffman's South American flux patch biasing the VGP path over the Americas [41]. The clustering of VGPs in the records of both the upper and lower Nunivak from locations in opposite hemispheres is difficult to explain as a present-day field overprint and instead provides support for the influence of a flux patch beneath South America.…”

Section: Polarity Transition Recordsmentioning

confidence: 97%

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Inner core anisotropy, anomalies in the time-averaged paleomagnetic field, and polarity transition paths

Clement

Stixrude

1995

Earth and Planetary Science Letters

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The diffusion of the dynamo-generated magnetic field into the electrically conducting inner core of the Earth may provide an explanation for several problematic aspects of long-term geomagnetic field behavior. We present a simple model which illustrates how an induced magnetization in the inner core which changes on diffusive timescales can provide a biasing field which could produce the observed anomalies in the time-averaged field and polarity reversals. The Earth's inner core exhibits an anisotropy in seismic velocities which can be explained by a preferred orientation of a polycrystalline aggregate of hexagonal close-packed (hcp) iron, an elastically anisotropic phase. Room temperature analogs of hcp iron also exhibit a strong anisotropy of magnetic susceptibility, ranging from 15 to 40% anisotropy. At inner core conditions the magnetic susceptibility of hcp iron is estimated to be between 10m4 and 10e3 SI. We speculate here that the anisotropy in magnetic susceptibility in the inner core could produce the observed anomalies in the time-averaged paleomagnetic field, polarity asymmetry, and recurring transitional virtual geomagnetic pole (VGP) positions.

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Section: Polarity Transition Recordsmentioning

confidence: 97%

“…3. The VGP paths during the upper and lower Nunivak polarity reversals recorded in Sicily [41] and Fiji. The records from opposite hemispheres yield remarkably similar VGP paths.…”

Section: Polarity Transition Recordsmentioning

confidence: 99%

Inner core anisotropy, anomalies in the time-averaged paleomagnetic field, and polarity transition paths

Clement

Stixrude

1995

Earth and Planetary Science Letters

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Relative geomagnetic field intensity and reversals from Upper Miocene sections in Crete

Làj

Kissel

Lefevre

1996

Earth and Planetary Science Letters

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When and why sediments fail to record the geomagnetic field during polarity reversals

Valet

Meynadier

Simon

et al. 2016

Earth and Planetary Science Letters

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International audienceWe present four new records of the Matuyama–Brunhes (M–B) reversal from sediments of the Equatorial Indian Ocean, West Equatorial Pacific and North Atlantic Oceans with deposition rates between 2 cm/kyr and 4.5 cm/kyr. The magnetic measurements were performed using 8 cc cubic samples and provided well-defined reverse and normal polarity directions prior and after the last reversal. In three records stepwise demagnetization of the transitional samples revealed a succession of scattered directions instead of a well-defined characteristic component of magnetization. There is no relationship with changes in magnetic mineralogy, magnetic concentration and magnetic grain sizes. This behavior could be caused by weakly magnetized sediment. However the transitional samples of two cores have almost three orders of magnitude stronger magnetizations than the non-transitional samples that yielded unambiguous primary directions in the other two cores. Moreover a similar proportion of magnetic grains was aligned in all records. Therefore, the large amount of magnetic grains oriented by the weak transitional field did not contribute to improve the definition of the characteristic component. We infer that the weakness of the field might not be only responsible. Assuming that the transitional period is dominated by a multipolar field, it is likely that the rapidly moving non-dipole components generated different directions that were recorded over the 2 cm stratigraphic thickness of each sample. These components are carried by grains with similar magnetic properties yielding scattered directions during demagnetization. In contrast, the strongly magnetized sediments of the fourth core from the West Equatorial Pacific Ocean were exempt of problems during demagnetization. The declinations rotate smoothly between the two polarities while the inclinations remain close to zero. This scenario results from post-depositional realignment that integrated various amounts of pre-and post-transitional magnetic directions within each sample. The present results point out the impossibility of extracting reliable information on geomagnetic reversals from low-medium deposition rate sediments with the current sampling techniques. Among other features, they put in question the relationship between reversal duration and site latitude

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The upper and lower Nunivak sedimentary geomagnetic transitional records from southern Sicily

Cited by 11 publications

References 27 publications

Inner core anisotropy, anomalies in the time-averaged paleomagnetic field, and polarity transition paths

Inner core anisotropy, anomalies in the time-averaged paleomagnetic field, and polarity transition paths

Relative geomagnetic field intensity and reversals from Upper Miocene sections in Crete

When and why sediments fail to record the geomagnetic field during polarity reversals

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