Speleothems as Magnetic Archives: Paleosecular Variation and a Relative Paleointensity Record From a Portuguese Speleothem

Ponte, Jorge; Font, Eric; Veiga-Pires, C.; Hillaire‐Marcel, Claude

doi:10.1029/2018gc007651

Cited by 7 publications

(14 citation statements)

References 48 publications

(136 reference statements)

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“…In addition, chemical sedimentary rocks, such as flowstones or speleothems, which form through the precipitation of minerals, have the potential to record the palaeomagnetic field and are used in an increasing number of studies (e.g. Lascu and Feinberg, 2011;Ponte et al, 2018;Zanella et al, 2018). Although the age of the first magnetization recorded on Earth (∼4.2 Ga) is currently debated (Tarduno et al, 2015;Weiss et al, 2018) the Earth is likely to have had a magnetic field as long ago as 3.5 Ga (Tarduno et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Refining Holocene geochronologies using palaeomagnetic records

Korte

Brown

Gunnarson

et al. 2019

Quaternary Geochronology

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The aperiodic nature of geomagnetic field variations, both in intensity and direction, can aid in dating archaeological artefacts, volcanic rocks, and sediment records that carry a palaeomagnetic signal. The success of palaeomagnetic dating relies upon our knowledge of past field variations at specific locations. Regional archaeo-and palaeomagnetic reference curves and predictions from global geomagnetic field models provide our best description of field variations through the Holocene. State-of-the-art palaeomagnetic laboratory practices and accurate independent age controls are prerequisites for deriving reliable reference curves and models from archaeological, volcanic, and sedimentary palaeomagnetic data. In this review paper we give an overview of these prerequisites and the available reference curves and models, discuss techniques for palaeomagnetic dating, and outline its limitations. In particular, palaeomagnetic dating on its own cannot give unique results, but rather serves to refine or confirm ages obtained by other methods. Owing

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Section: Introductionmentioning

confidence: 99%

Refining Holocene geochronologies using palaeomagnetic records

Korte

Brown

Gunnarson

et al. 2019

Quaternary Geochronology

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“…Other archives for recording the paleomagnetic field include wind‐blown loess‐paleosol sediments, for example, sections from the Chinese Loess Plateau (Li et al, ; Pan et al, ; Zhu et al, ), and cave sediments and speleothems (e.g., Bourne et al, ; Lascu & Feinberg, ; Ponte et al, ; Ponte et al, ; Trindade et al, ; Zanella et al, ). The latter are cave formations that can provide high‐resolution records of geomagnetic excursions (Lascu et al, ; Lascu & Feinberg, ), for example, recently, Chou et al () presented a multidecadally resolved geomagnetic excursion (107–91 ka) in a Chinese stalagmite.…”

Section: Data On the Past Geomagnetic Fieldmentioning

confidence: 99%

One Hundred Thousand Years of Geomagnetic Field Evolution

Panovska

Korte

Constable

2019

Reviews of Geophysics

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Paleomagnetic records from sediments, archeological artifacts, and lava flows provide the foundation for studying geomagnetic field changes over 0-100 ka. Late Quaternary time-varying spherical harmonic models for 0-100 ka produce a global view used to evaluate new data records, study the paleomagnetic secular variation on centennial to multimillennial timescales, and investigate extreme regional or global events such as the Laschamp geomagnetic excursion. Recent modeling results (GGF100k and LSMOD.2) are compared to previous studies based on regional or global stacks and averages of relative geomagnetic paleointensity variations. Time-averaged field structure is similar on Holocene, 100 ky, and million-year timescales. Paleosecular variation activity varies greatly over 0-100 ka, with large changes in field strength and significant morphological changes that are especially evident when field strength is low. GGF100k exhibits a factor of 4 variation in geomagnetic axial dipole moment, and higher-resolution models suggest that much larger changes are likely during global excursions. There is some suggestion of recurrent field states resembling the present-day South Atlantic Anomaly, but these are not linked to initiation or evolution of excursions. Several properties used to characterize numerical dynamo simulations as "Earth-like" are evaluated and, in future, improved models may yet reveal systematic changes linked to the onset of geomagnetic excursions. Modeling results are useful in applications ranging from ground truth and data assimilation in geodynamo simulations to providing geochronological constraints and modeling the influence of geomagnetic variations on cosmogenic isotope production rates. Plain Language SummaryEarth's magnetic field is generated by dynamo activity in the planet's liquid outer core. It provides the foundation for modern navigation, protects us from space weather, and through its variations over time provides a mechanism for studying the deep interior of our planet. On timescales beyond a few centuries there are no direct observations, and paleomagnetic records from sediments, archeological artifacts, and lava flows are used for studying the geomagnetic field. They provide a global view of the field used to evaluate new data records, study the field changes (known as paleosecular variation) on centennial to multimillennial timescales, and investigate extreme regional or global events. The average field structure is similar on 10 ky, 100 ky, and million-year timescales. The magnetic dipole moment varies by at least a factor of 4 over 0-100 ka, with higher-resolution models suggesting much larger changes during global excursions. Recent results provide a global view, allowing analysis of geomagnetic excursions, including the Laschamp excursion. Results are useful in applications ranging from ground truth and data assimilation in numerical geodynamo simulations, to providing age constraints for climate records, archeological artifacts, and sediments and for studying impact of Earth's mag...

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“…Meanwhile, although speleothem characteristics re ect local environmental changes such as climate, soil, and host-rock conditions (Fairchild and Baker, 2012), previous studies on speleothem magnetism were reported only from limited continental regions; namely in Europe (e.g., Zanella et al, 2018;Ponte et al, 2018), north and south America (e.g., Lascu et al, 2016;Jaqueto et al, 2016), and East Asia (e.g., Zhu et al, 2017: Chen et al, 2019.…”

Section: Introductionmentioning

confidence: 99%

High spatial resolution magnetic mapping using ultra-high sensitivity scanning SQUID microscopy on a speleothem from the Kingdom of Tonga, southern Pacific

Fukuyo

Oda

Yokoyama

et al. 2020

Preprint

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Speleothems are an ideal archive of paleomagnetism since they retain continuous geomagnetic records in stable conditions and can be used for reliable radiometric dating using U-series and radiocarbon methods. However, their weak magnetic signals hinder the widespread use of this archive in the field of geoscience. While previous studies successfully reconstructed paleomagnetic signatures, including geomagnetic excursions, the time resolutions presented were not sufficient. Recently emerging scanning SQUID microscopy (SSM) in this field can image very weak magnetic fields while maintaining high spatial resolution that could likely overcome this obstacle. In this study, we employed SSM for paleomagnetic measurements on a stalagmite collected at Anahulu cave in Tongatapu Island, the Kingdom of Tonga. The samples were sliced to a thickness of ca. 0.2 mm and scanned for NRM using SSM, and the signal provides the indications of the influence from viscous remanent magnetization. It was thus removed by alternating field demagnetization (AFD) at 5mT. The average measured magnetic field after 5 mT AFD is ca. 0.27 nT with a sensor-to-sample distance of ~200 µm. A stronger magnetic field (average: ca. 0.62 nT) was observed above the grayish surface layer compared to that of the white inner layer (average: ca. 0.09 nT) associated with the laminated structures of a speleothem at the submillimeter scale with the SSM. The magnetization of the speleothem sample calculated by an inversion of isothermal remanent magnetization (IRM) also suggests that magnetic mineral content in the surface layer is higher than the inner layer. This feature was further investigated by low-temperature magnetometry. The results reveal that it contains magnetite and maghemite. The first-order reversal curve (FORC) measurements and the decomposition of IRM curves show that this speleothem contains a mixture of magnetic minerals with different coercivities and domain states. The contribution from maghemite to the total magnetization of the grayish surface layer is much higher than the white inner layer. The gray and white-colored layers of the speleothem retaining magnetically distinct characters indicates that the depositional environment was shifted when the surface layer was deposited and was likely changed to the oxidative environment.

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Speleothems as Magnetic Archives: Paleosecular Variation and a Relative Paleointensity Record From a Portuguese Speleothem

Cited by 7 publications

References 48 publications

Refining Holocene geochronologies using palaeomagnetic records

Refining Holocene geochronologies using palaeomagnetic records

One Hundred Thousand Years of Geomagnetic Field Evolution

High spatial resolution magnetic mapping using ultra-high sensitivity scanning SQUID microscopy on a speleothem from the Kingdom of Tonga, southern Pacific

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