An analysis of geomagnetic field reversals supports the validity of the Geocentric Axial Dipole (GAD) hypothesis in the Precambrian

2014 ◽  
Vol 244 ◽  
pp. 33-41 ◽  
Author(s):  
Toni Veikkolainen ◽  
Lauri Pesonen ◽  
Kimmo Korhonen
Keyword(s):  
Geomagnetic Field ◽  
Axial Dipole ◽  
Geocentric Axial Dipole

V. The remanent magnetization of unstable Keuper Marls

1957 ◽  
Vol 250 (974) ◽  
pp. 130-143 ◽  
Keyword(s):  
Geomagnetic Field ◽  
Remanent Magnetization ◽  
Laboratory Experiments ◽  
Natural Remanent Magnetization ◽  
Single Domain ◽  
Dipole Field ◽  
Main Field ◽  
Axial Dipole ◽  
Geocentric Axial Dipole ◽  
Three Components

Measurements of the directions and intensities of magnetization of Keuper Marls from Sidmouth are described. The natural remanent magnetization of these rocks is shown to be unstable in the geomagnetic field. Certain laboratory experiments are described which show the natural remanent magnetization to consist of three components, a primary component created on, or soon after, deposition, in the same direction as that of the natural remanent magnetization of Keuper Sandstones and Marls described by Clegg, Almond & Stubbs (1954); a secondary component in the direction of a geocentric axial dipole field in Britain acquired since the last reversal of the main field and a temporary component built up by the geomagnetic field between collection and measurement. The temporary and secondary components are believed to be isothermal remanent magnetizations and to be due to the red haematite cement. Application of Néel’s theory of the magnetization of small single-domain particles shows that haematite grains of less than 0·15 μ in diameter will be magnetically unstable. The temporary and secondary components of magnetization are explained in terms of Néel’s theory. A suggested test of stability is described.

scholarly journals Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Andrew J. Biggin ◽  
Richard K. Bono ◽  
Domenico G. Meduri ◽  
Courtney J. Sprain ◽  
Christopher J. Davies ◽  
...  
Keyword(s):  
Power Law ◽  
Geomagnetic Field ◽  
Recent Observation ◽  
Observational Constraint ◽  
Angular Dispersion ◽  
Geological Time ◽  
Future Studies ◽  
Axial Dipole ◽  
Quantitative Estimates

AbstractA defining characteristic of the recent geomagnetic field is its dominant axial dipole which provides its navigational utility and dictates the shape of the magnetosphere. Going back through time, much less is known about the degree of axial dipole dominance. Here we use a substantial and diverse set of 3D numerical dynamo simulations and recent observation-based field models to derive a power law relationship between the angular dispersion of virtual geomagnetic poles at the equator and the median axial dipole dominance measured at Earth’s surface. Applying this relation to published estimates of equatorial angular dispersion implies that geomagnetic axial dipole dominance averaged over 107–109 years has remained moderately high and stable through large parts of geological time. This provides an observational constraint to future studies of the geodynamo and palaeomagnetosphere. It also provides some reassurance as to the reliability of palaeogeographical reconstructions provided by palaeomagnetism.

A test of the geocentric axial dipole hypothesis from an analysis of the skewness of the central marine magnetic anomaly

1996 ◽  
Vol 144 (3-4) ◽  
pp. 337-346 ◽  
Author(s):  
Gary D. Acton ◽  
Katerina E. Petronotis ◽  
Cheryl D. Cape ◽  
Sue Rotto Ilg ◽  
Richard G. Gordon ◽  
...  
Keyword(s):  
Magnetic Anomaly ◽  
Axial Dipole ◽  
Geocentric Axial Dipole

Challenging the dipolar paradigm for Proterozoic Earth

2022 ◽  
Author(s):  
James W. Sears
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Inner Core ◽  
Ultraviolet B ◽  
Late Permian ◽  
Early Paleozoic ◽  
Thin Spherical Shell ◽  
Late Neoproterozoic ◽  
Geocentric Axial Dipole ◽  
Drift Path

ABSTRACT A robust, geology-based Proterozoic continental assembly places the northern and eastern margins of the Siberian craton against the southwestern margins of Laurentia in a tight, spoon-in-spoon conjugate fit. The proposed assembly began to break apart in late Neoproterozoic and early Paleozoic time. Siberia then drifted clockwise along the Laurussian margin on coast-parallel transforms until suturing with Europe in late Permian time. The proposed drift path is permitted by a geocentric axial dipole (GAD) magnetic field from Silurian to Permian time. However, the Proterozoic reconstruction itself is not permitted by GAD. Rather, site-mean paleomagnetic data plot ted on the reconstruction suggest a multipolar Proterozoic dynamo dominated by a quadrupole. The field may have resembled that of present-day Neptune, where, in the absence of a large solid inner core, a quadrupolar magnetic field may be generated within a thin spherical shell near the core-mantle boundary. The quadrupole may have dominated Earth’s geomagnetic field until early Paleozoic time, when the field became erratic and transitioned to a dipole, which overwhelmed the weaker quadrupole. The dipole then established a strong magnetosphere, effectively shielding Earth from ultraviolet-B (UV-B) radiation and making the planet habitable for Cambrian fauna.

scholarly journals Elevated paleomagnetic dispersion at Saint Helena suggests long-lived anomalous behavior in the South Atlantic

2020 ◽  
Vol 117 (31) ◽  
pp. 18258-18263 ◽  
Author(s):  
Yael A. Engbers ◽  
Andrew J. Biggin ◽  
Richard K. Bono
Keyword(s):  
Geomagnetic Field ◽  
Anomalous Behavior ◽  
Magnetic Polarity ◽  
South Atlantic ◽  
Polarity Reversal ◽  
The South ◽  
Geomagnetic Secular Variation ◽  
Core Dynamics ◽  
Geocentric Axial Dipole ◽  
Magnetic Polarity Reversal

Earth’s magnetic field is presently characterized by a large and growing anomaly in the South Atlantic Ocean. The question of whether this region of Earth’s surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics, core−mantle interaction, and the possibility of an imminent magnetic polarity reversal. Here we present paleomagnetic data from Saint Helena, a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the South Atlantic on timescales of millions of years. Our results, supported by positive baked contact and reversal tests, produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago, but with very large associated directional dispersion. These findings indicate that, on geological timescales, geomagnetic secular variation is persistently enhanced in the vicinity of Saint Helena. This, in turn, supports the South Atlantic as a locus of unusual geomagnetic behavior arising from core−mantle interaction, while also appearing to reduce the likelihood that the present-day regional anomaly is a precursor to a global polarity reversal.

scholarly journals A full sequence of the Matuyama–Brunhes geomagnetic reversal in the Chiba composite section, Central Japan

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Yuki Haneda ◽  
Makoto Okada ◽  
Yusuke Suganuma ◽  
Takahiro Kitamura
Keyword(s):  
Field Intensity ◽  
Geomagnetic Field ◽  
Central Japan ◽  
Virtual Geomagnetic Pole ◽  
Geomagnetic Reversal ◽  
Full Sequence ◽  
Intensity Index ◽  
Axial Dipole ◽  
Composite Section ◽  
Stratigraphic Position

Abstract Geological records of the Matuyama–Brunhes (M–B) geomagnetic reversal facilitate the development of an age model for sedimentary and volcanic sequences and help decipher the dynamics of the Earth’s magnetic field. However, the structure of the geomagnetic field during the M–B geomagnetic reversal remains controversial due to its complex field behavior. In this study, we conducted paleo- and rock-magnetic analyses of samples from the Chiba composite section (CbCS), a continuous and expanded marine succession in Central Japan, to reconstruct the full sequence of the M–B geomagnetic reversal. We define an average stratigraphic position of the M–B boundary and estimate its age based on three sections in the CbCS and a neighboring drill core, TB-2. The average stratigraphic position of the M–B boundary in the CbCS is established at 1.1 ± 0.3 m above a widespread volcanic ash bed (the Byk-E tephra). Assuming a chronological error associated with orbital tuning of 5 kyr and stratigraphic uncertainty of 0.4 kyr, the M–B boundary in CbCS is at 772.9 ± 5.4 ka (1σ). The virtual geomagnetic pole, which is calculated from the paleomagnetic directions, shows several short fluctuations between 783 and 763 ka, with concomitant decreases in geomagnetic field intensity index. After termination of the field instabilities, the field intensity recovered and became higher than before the M–B boundary, with a stable normal polarity direction. The paleomagnetic records in the CbCS exhibit a field asymmetry between the axial dipole decay and field recovery, providing a full sequence of the M–B reversal, suggesting that the non-axial dipole field dominated several times during periods ca. 20 kyr long across the M–B boundary, due to depletion in the main axial dipole component. Our results provide probably the most detailed sedimentary record of the M–B geomagnetic reversal and offer valuable information to further understand the mechanism and dynamics of geomagnetic reversals. Graphical abstract

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