Intensity of the Earth's magnetic field: Evidence for a Mid-Paleozoic dipole low

Hawkins, Louise; Grappone, J. Michael; Sprain, Courtney J.; Saengduean, Patipan; Sage, Edward; Thomas-Cunningham, Sheikerra; Kugabalan, Banusha; Biggin, Andrew J.

doi:10.1073/pnas.2017342118

Cited by 25 publications

(10 citation statements)

References 44 publications

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“…However, a middle Visean high reversal frequency seems compatible with current datasets from the Late Devonian (gray curve in Figure 13; Green et al., 2021; curve from Hounslow, 2022). It is further consistent with the very low paleointensity estimates recovered from the coeval Kinghorn Volcanics that define the youngest point of the “mid‐Paleozoic Dipole Low” (Hawkins et al., 2021). The fact that the mid‐Paleozoic is temporally equidistant to the Middle Jurassic and the Late Ediacaran is suggestive of a ∼200 Myr quasi‐cyclicity in paleomagnetic field behavior (Biggin et al., 2012).…”

Section: Discussionsupporting

confidence: 82%

A Hyperactive Geomagnetic Field in the Late Visean (Early Carboniferous) From the Late Asbian Stratotype Section in Northwest England, UK

Hounslow,

Biggin,

Cózar

et al. 2024

Geochem Geophys Geosyst

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Plain Language SummaryNearly synchronous global changes in geomagnetic polarity give both a detailed irregular pacing to geological time and provide a glimpse into heat transfer processes across the core—mantle boundary which drives the Earth's geodynamo. Although the Late Carboniferous is characterized by some well‐studied reversals, details of the tempo of polarity changes in the Early Carboniferous are unknown. This work addresses this by providing a detailed record of polarity changes over a ∼2 million year interval at around 334.5–332.5 million years ago‐from the Trowbarrow Quarry section in NW England. We demonstrate that these limestones likely preserve magnetization from close to their time of formation and record at least 31 polarity reversals. These observations support the idea that the Earth's dynamo was in a hyperactive reversing state similar to those sustained for tens of Myr in the Late Jurassic, parts of the Cambrian and the Late Ediacaran. It further corroborates a ∼200 Myr cyclicity in paleomagnetic field behavior since the Precambrian, potentially linked to variable core heat flow forced by mantle convection.

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Section: Discussionsupporting

confidence: 82%

A Hyperactive Geomagnetic Field in the Late Visean (Early Carboniferous) From the Late Asbian Stratotype Section in Northwest England, UK

Hounslow,

Biggin,

Cózar

et al. 2024

Geochem Geophys Geosyst

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“…Our new findings regarding the PCRS appear to rule out the second scenario (since the axial dipole does appear to have been enhanced at the expense of the rest of the field during this time). The observation that average VDM also appears to have been elevated during the PCRS (Hawkins et al., 2021) rather supports the first scenario, or somewhere on the spectrum near to it. Likewise, if the duration of the MDL was shown to coincide with the time interval represented by the combined Pre‐CNS and Post‐PCRS then this could suggest that an increased contribution from the non‐axial dipole field was a factor in the lower average VDM.…”

Section: Discussionmentioning

confidence: 96%

Analyzing Triassic and Permian Geomagnetic Paleosecular Variation and the Implications for Ancient Field Morphology

Handford

Biggin

Haldan

et al. 2021

Geochem Geophys Geosyst

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The geomagnetic field exists as a consequence of a dynamic system and shows variations across a range of timescales (Johnson & McFadden, 2015). Long-term behavior is often described in terms of the intensity, reversal rate, morphology, and stability of the field. As all of these features are a result of the geodynamo, it follows that their variations should be intrinsically linked and that relationships may exist between them (

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“…The efficiency of the magnetic field since 450 Ma has been governed by zonal and non-zonal variations in core-mantle boundary heat flow 55 superimposed on the dominant degree-2 deep mantle structure, as evidenced by variations in paleointensity and reversal frequency since the early developments of Pangea in the Devonian on ~200 Myr time scales 7,11,17,19,20,[56][57][58] . But post ~450 Ma convection has not changed the dominant degree-2 mantle structure, which remains as the principal factor controlling the nature of inner core growth.…”

Section: Discussionmentioning

confidence: 99%

Early Cambrian renewal of the geodynamo and the origin of inner core structure

et al. 2022

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Paleomagnetism can elucidate the origin of inner core structure by establishing when crystallization started. The salient signal is an ultralow field strength, associated with waning thermal energy to power the geodynamo from core-mantle heat flux, followed by a sharp intensity increase as new thermal and compositional sources of buoyancy become available once inner core nucleation (ICN) commences. Ultralow fields have been reported from Ediacaran (~565 Ma) rocks, but the transition to stronger strengths has been unclear. Herein, we present single crystal paleointensity results from early Cambrian (~532 Ma) anorthosites of Oklahoma. These yield a time-averaged dipole moment 5 times greater than that of the Ediacaran Period. This rapid renewal of the field, together with data defining ultralow strengths, constrains ICN to ~550 Ma. Thermal modeling using this onset age suggests the inner core had grown to 50% of its current radius, where seismic anisotropy changes, by ~450 Ma. We propose the seismic anisotropy of the outermost inner core reflects development of a global spherical harmonic degree-2 deep mantle structure at this time that has persisted to the present day. The imprint of an older degree-1 pattern is preserved in the innermost inner core.

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Intensity of the Earth's magnetic field: Evidence for a Mid-Paleozoic dipole low

Cited by 25 publications

References 44 publications

A Hyperactive Geomagnetic Field in the Late Visean (Early Carboniferous) From the Late Asbian Stratotype Section in Northwest England, UK

A Hyperactive Geomagnetic Field in the Late Visean (Early Carboniferous) From the Late Asbian Stratotype Section in Northwest England, UK

Analyzing Triassic and Permian Geomagnetic Paleosecular Variation and the Implications for Ancient Field Morphology

Early Cambrian renewal of the geodynamo and the origin of inner core structure

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