Relative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the Açores area

doi:10.1016/0031-9201(95)03070-0

Physics of the Earth and Planetary Interiors

Volume 93, Issues 3–4, February 1996, Pages 269-284

https://doi.org/10.1016/0031-9201(95)03070-0 Get rights and content

Abstract

Relative changes in geomagnetic field intensity over the last 280 kyears have been recovered from the study of three marine cores from the Açores area. One core was precisely dated by oxygen isotope study and the other two records were linked to it using light reflectance analysis which allowed precise correlation. Rock magnetic analysis shows that the main magnetic mineral is magnetite with a very homogeneous grain-size distribution in the pseudo-single domain range for the three cores. Changes in the amount of magnetite do not exceed a factor of 10. Therefore, these cores appear to be suitable for relative palaeointensity determinations. Two mineral magnetic components with periodicities of 23 and 18 kyears are present in the records of bulk magnetic parameters and natural remanent magnetisation (NRM), but the power at these frequencies is not significant at the 95% level for the normalised remanence records. For each core, normalisation of the NRM using different normalising parameters yields virtually identical results. Using saturation isothermal remanent magnetisation (SIRM) as the normalising parameter, the results of the three cores were then combined into a stacked curve. Squared coherence analysis between this stacked curve and bulk mineral-magnetic parameters reveals that the 18 kyear component is still present in the record, but that the power spectrum is barely above noise level at this frequency. Some of the features of this North Atlantic record are consistent with the main characteristics already documented in other sedimentary or volcanic records. For instance, distinct periods of low intensity are observed around 40, 120, and 190 kyears, and periods of high intensity at 50 and 80 kyears. Because of the uniformity of the mineral-magnetic characteristics of the three cores, we suggest that this record may be a suitable palaeointensity reference curve for the Central North Atlantic Ocean region.

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40Ar/39Ar incremental heating experiments on lavas that record the Skálamælifell excursion, coupled with 238U/230Th data from two of these lavas, yield a weighted mean age of 94.1 ± 7.8 ka for the excursion. The new age for the excursion is more than twice as old as the unspiked K–Ar ages for these lavas (Levi et al., 1990), yet the new age is in excellent agreement with the timing of paleointensity lows that are observed at globally dispersed sites including sediment cores in the north Atlantic (ODP sites 919, 983, 984) (Channell, 1999, 2006; Channell et al., 1997) and Labrador Sea (Stoner et al., 2000), sedimentary stacks from the Portuguese margin (Thouveny et al., 2004) and the Azores (Lehman et al., 1996), as well as a sequence of lavas from Réunion Island in the southern Indian Ocean (Raïs et al., 1996). The ~ 94 ka Skálamælifell excursion coincides with the second of two distinct global paleointensity lows that occurred during a period of geomagnetic instability from 125–90 ka.
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Research paperRelative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the Açores area

Abstract

A rapid method for magnetic granulometry with applications to environmental studies

Geophys. Res. Lett.

Abrupt color changes in isotope stage 5 in North Atlantic deep sea cores: Implications for rapid change of climate-driven events

Evidence for a new geomagnetic reversal from lava flows in Idaho: discussion of short polarity reversals in the Brunhes and late Matuyama Polarity Chrons

J. Geophys. Res.

Paleointensity of the Earth's magnetic field and KAr dating of the Louchardière volcanic flow (central France): new evidence for the Laschamp excursion

Geophys. Res. Lett.

Palaeointensity in the pelagic realm: marine sediment data compared with archaeomagnetic and lake sediment records

Geophys. J.R. Astron. Soc.

Hysteresis properties of titano-magnetite: grain-size and compositional dependence

Phys. Earth Planet. Inter.

Age and correlation of paleomagnetic episode in the western United States by 40Ar/39Ar dating and tephrochronology: The Jamaica, Blake, or a new polarity episode?

J. Geophys. Res.

A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials. Some results for lake sediments

Earth Planet. Sci. Lett.

Sedimentary magnetism, environmental magnetism, and magnetostratigraphy

US Natl. Rep. Int. Union Geod. Geophys. 1987–1990

Rev. Geophys.

A new rock magnetic approach for selecting sediments for geomagnetic paleointensity studies: application to paleointensity for the last 4000 years

J. Geophys. Res.

Improvements in selection criteria for sedimentary geomagnetic paleointensity determinations based on magnetic hysteresis characteristics of sediments from the Central North Atlantic Ocean

Trans. Am. Geophys. Union (EOS)

On the possibility of obtaining relative paleointensities from sediments

Earth Planet. Sci. Lett.

Age dating and the orbital theory of the ice ages: Development of a high resolution 0–300000 years stratigraphy

Quat. Res.

Relative geomagnetic intensity of the field during the last 140 ka

Earth Planet. Sci. Lett.

Research paper
Relative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the Açores area