Microwave palaeointensity results from the Matuyama–Brunhes geomagnetic field reversal

Brown, M. C.; Gratton, M. N.; Shaw, John; Holme, Richard; Soler, Vicente

doi:10.1016/j.pepi.2008.11.001

Cited by 15 publications

(17 citation statements)

References 116 publications

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“…In addition, it has been shown that geomagnetic excursions are associated with higher MAD values in loess samples [Yang et al, 2007;Spassov et al, 2011] because of the low alignment efficiency of the magnetic particles [Jin and Liu, 2011b]. In the case of unit L9 of the GL loess, we suggest that the normal polarity ChRM isolated by AFD (Figure 8c), corresponding to low values of NRM x /NRM and to high values of MAD AFD (Figure 8d), and which cannot be readily correlated to features such as the Kamikatsura and Santa Rosa excursions of the standard GPTS, may represent two possible conditions: (i) On the one hand, during the course of the Kamikatsura (880-886 ka) [Singer et al, 1999] and Santa Rosa (936 ka) [Singer and Brown, 2002] events, the polarity of the ChRM changes to normal, and because of the weak paleointensity during these two events Gratton et al, 2007;Brown et al, 2009;Leonhardt et al, 2009] there was a relatively low alignment efficiency of the magnetic particles [Jin and Liu, 2011b]. Accordingly, values of NRM x / NRM are reduced and MAD values increased [Yang et al, 2007;Spassov et al, 2011].…”

Section: And €mentioning

confidence: 99%

An investigation of the magnetic carriers and demagnetization characteristics of the Gulang loess section, northwestern Chinese Loess Plateau

Chen

Qiang

Zhao

et al. 2014

Geochem. Geophys. Geosyst.

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We report the results of a rock magnetic and paleomagnetic investigation of unit L9 of the Gulang (GL) loess section, in the northwestern Chinese Loess Plateau (CLP). We demonstrate that the dominant magnetic remanence carriers are coarse-grained pseudo single-domain/multidomain magnetite particles, and hematite. The application of either thermal (THD) or alternating-field demagnetization (AFD) yielded several normal polarity intervals interbedded with intervals of reversed polarity, but which cannot be correlated with standard geomagnetic polarity time scales. A greater number of normal polarity intervals, however, were evident after THD than after AFD. We propose that the normal polarities are either the result of overprinting of a viscous remanent magnetization (VRM) carried by coarse magnetite particles on the original depositional remanent magnetization (DRM); or that they represent genuine geomagnetic excursions (such as the Kamikatsura and Santa Rosa excursions) which are difficult to identify. In addition, we propose that in the case of the GL loess section, the effect of thermal demagnetization tails of a VRM is a possible reason why THD treatment yielded a greater number of normal polarity intervals than does AFD. However, reversed polarities obtained by either THD or AFD may be credible for sedimentary intervals with a relatively high content of hematite particles which preserve the primary DRM. Although numerous studies have proposed that THD provides more reliable paleomagnetic directions for loess sediments from the CLP, our results suggest that careful attention needs to be paid to the type of demagnetization method chosen, especially in the case of coarse-grained loess deposits.

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Section: And €mentioning

confidence: 99%

An investigation of the magnetic carriers and demagnetization characteristics of the Gulang loess section, northwestern Chinese Loess Plateau

Chen

Qiang

Zhao

et al. 2014

Geochem. Geophys. Geosyst.

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“…Precise paleomagnetic data of polarity reversals are crucial for understanding the geomagnetic field and have been expected to constrain geodynamo models in the deep interior of the Earth. Paleointensity studies on volcanic rocks have shown that the geomagnetic field intensity during polarity reversals is quite low, and is 1/10 ∼ 1/3 of the nontransitional field intensity [e.g., Prévot et al , 1985; Quidelleur and Valet , 1996; Valet et al , 1999; Brown et al , 2009]. It is widely accepted that the field intensity drops prior to major directional changes and recovers after them [e.g., Merrill and McFadden , 1999; Brown et al , 2009].…”

Section: Introductionmentioning

confidence: 99%

“…Paleointensity studies on volcanic rocks have shown that the geomagnetic field intensity during polarity reversals is quite low, and is 1/10 ∼ 1/3 of the nontransitional field intensity [e.g., Prévot et al , 1985; Quidelleur and Valet , 1996; Valet et al , 1999; Brown et al , 2009]. It is widely accepted that the field intensity drops prior to major directional changes and recovers after them [e.g., Merrill and McFadden , 1999; Brown et al , 2009]. In other words, the decrease of the geocentric axial dipole (GAD) occurs at the onset of polarity reversals, suggesting that the GAD intensity change is vital for the geodynamo at the onset of polarity reversals.…”

Section: Introductionmentioning

confidence: 99%

“…For the M‐B transition, paleomagnetic records of successive lava flows have been reported from six localities; Iceland [ Kristjansson et al , 1988], Tahiti [ Chauvin et al , 1990], Maui [ Baksi et al , 1992; Coe et al , 2004], Chile [ Brown et al , 1994, 2004], La Palma [e.g., Quidelleur and Valet , 1996; Valet et al , 1999], and La Guadeloupe Island [ Carlut et al , 2000]. To date, successive paleointensity data were reported from two of these localities; La Palma [ Quidelleur and Valet , 1996; Valet et al , 1999; Brown et al , 2009] and Chile [ Gratton et al , 2007].…”

Section: Introductionmentioning

confidence: 99%

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Paleointensity variation across the Matuyama-Brunhes polarity transition: Observations from lavas at Punaruu Valley, Tahiti

et al. 2011

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[1] We have conducted a paleointensity study of the Matuyama-Brunhes (M-B) polarity transition recorded in 34 successive lava flows of Punaruu Valley on Tahiti. A reversed polarity is obtained from the lower part of the record, major directional changes are derived from the middle part of the record, and a normal polarity is recorded in the upper part of the record. These paleomagnetic directions and five 40 Ar/ 39 Ar ages yielding a weighted mean of 771 ± 8 (1s) ka indicate that 30 lava flows recorded the geomagnetic field across the M-B transition. The 215 specimens from 32 flows were subjected to the double-heating technique of the Shaw method combined with low-temperature demagnetization (LTD-DHT Shaw method), yielding 73 successful results from 18 flows. For the reversed polarity period just prior to the major directional changes, paleointensity shows an oscillation-like variation between 3 and 38 mT corresponding to virtual dipole moments (VDMs) between 0.9 × 10 22 and 9.6 × 10 22 Am 2 . For the major directional changes, a weak paleointensity of 5 mT is obtained, which gives a VDM of 1.0 × 10 22 Am 2 . For the normal polarity period, paleointensities are 14-21 mT, giving VDMs of 3.5-5.2 × 10 22 Am 2 . For the reversed polarity period just prior to the major directional changes, a linear relationship with a correlation coefficient of 0.96 is recognized on the diagram of VDM versus virtual geomagnetic pole latitude. This linear relationship may be a precursory feature of the geodynamo at the onset of the M-B transition.

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“…[] (hereafter referred to as C00), Carlut and Quidelleur [] (hereafter referred to as CQ00), and Brown et al . [] (hereafter referred to as B09). Based upon K‐Ar Cassignol‐Gillot ages [ Samper et al ., ], the island can be split into five broad volcanic complexes (Figure b): the Basal complex (2.79–2.69 Ma); Septentrional Chain (1.8–1.15 Ma); Axial Chain (1.02–0.44 Ma); Monts Caraïbes Massif (0.56–0.45 Ma); and Grande Découverte volcanic complex (0.20 Ma—present).…”

Section: Sampling Locationsmentioning

confidence: 99%

Snapshot of the Matuyama‐Brunhes reversal process recorded in ⁴⁰Ar/³⁹Ar‐dated lavas from Guadeloupe, West Indies

Brown

Jicha

Singer

et al. 2013

Geochem Geophys Geosyst

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[1] We obtain new 40 Ar/ 39Ar ages for three lavas that record part of the Matuyama-Brunhes geomagnetic field reversal process on Guadeloupe. These lavas record a reversed-transitional-reversed magnetostratigraphy and yield a weighted mean isochron age of 785.2 6 5.2 ka (2 analytical uncertainty) relative to an age for the Fish Canyon sanidine standard of 28.201 Ma. This age is of greater accuracy than ages obtained previously by K-Ar dating. These lavas may record directional fluctuations occurring between the Matuyama-Brunhes precursor and the final directional reversal. Such variations have been observed in some globally distributed coupled paleomagnetic and oxygen isotope marine sedimentary records of the Matuyama-Brunhes reversal. Previous paleointensity estimates from these lavas indicate reduced, but fluctuating field strength during this time.

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Microwave palaeointensity results from the Matuyama–Brunhes geomagnetic field reversal

Cited by 15 publications

References 116 publications

An investigation of the magnetic carriers and demagnetization characteristics of the Gulang loess section, northwestern Chinese Loess Plateau

An investigation of the magnetic carriers and demagnetization characteristics of the Gulang loess section, northwestern Chinese Loess Plateau

Paleointensity variation across the Matuyama-Brunhes polarity transition: Observations from lavas at Punaruu Valley, Tahiti

Snapshot of the Matuyama‐Brunhes reversal process recorded in ⁴⁰Ar/³⁹Ar‐dated lavas from Guadeloupe, West Indies

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Microwave palaeointensity results from the Matuyama–Brunhes geomagnetic field reversal

Cited by 15 publications

References 116 publications

An investigation of the magnetic carriers and demagnetization characteristics of the Gulang loess section, northwestern Chinese Loess Plateau

An investigation of the magnetic carriers and demagnetization characteristics of the Gulang loess section, northwestern Chinese Loess Plateau

Paleointensity variation across the Matuyama-Brunhes polarity transition: Observations from lavas at Punaruu Valley, Tahiti

Snapshot of the Matuyama‐Brunhes reversal process recorded in 40Ar/39Ar‐dated lavas from Guadeloupe, West Indies

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Snapshot of the Matuyama‐Brunhes reversal process recorded in ⁴⁰Ar/³⁹Ar‐dated lavas from Guadeloupe, West Indies