The Complexity of Reversals

Coe, Robert S.; Glen, Jonathan M.G.

doi:10.1029/145gm16

Cited by 13 publications

(17 citation statements)

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“…This paper joint analysis of sediment and archeomagnetic and/or lava data allows the resolution of a greater degree of complexity in field behavior (e.g., Korte and Constable 2005). This is true for not only the past 50 ka, but in the case of lavas, over other geomagnetically interesting times, such as during reversals (e.g., Brown et al 2013;Coe and Glen 2004).…”

Section: Introductionmentioning

confidence: 99%

GEOMAGIA50.v3: 2. A new paleomagnetic database for lake and marine sediments

et al. 2015

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Background: GEOMAGIA50.v3 for sediments is a comprehensive online database providing access to published paleomagnetic, rock magnetic, and chronological data obtained from lake and marine sediments deposited over the past 50 ka. Its objective is to catalogue data that will improve our understanding of changes in the geomagnetic field, physical environments, and climate. Findings: GEOMAGIA50.v3 for sediments builds upon the structure of the pre-existing GEOMAGIA50 database for magnetic data from archeological and volcanic materials. A strong emphasis has been placed on the storage of geochronological data, and it is the first magnetic archive that includes comprehensive radiocarbon age data from sediments. The database will be updated as new sediment data become available. Conclusions:The web-based interface for the sediment database is located at http://geomagia.gfz-potsdam.de/ geomagiav3/SDquery.php. This paper is a companion to Brown et al. (Earth Planets Space doi:10.1186/s40623-015-0232-0, 2015 and describes the data types, structure, and functionality of the sediment database.

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Section: Introductionmentioning

confidence: 99%

GEOMAGIA50.v3: 2. A new paleomagnetic database for lake and marine sediments

et al. 2015

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“…We recalibrated all previously published 40 Ar/ 39 Ar ages to the same 40 K decay constants and the FCTs standard age used for the Tahitian samples. Dated samples from the Maui site extend back to 785.1 ± 8.0 ka (Coe et al, ), while the La Palma and Chile samples largely occur between ∼790 and 810 ka, coincident with the precursor phase (Singer et al, ). VGP latitudes from these flows that are older than the M‐B reversal range from reversed to normal, with a number of transitional directions clustered in the southern low latitudes.…”

Section: Discussionmentioning

confidence: 99%

“… Virtual geomagnetic pole (VGP) latitudes through time of all reported field sites that record the M‐B reversal (Coe et al, ; Singer et al, ) with their corresponding probability density functions (PDF). The PDF curves incorporate only samples with latitudinal VGPs between −45° and 90°, which we interpret as indicating instability during the Matuyama chron.…”

Section: Discussionmentioning

confidence: 99%

“…(top) All lava flow records from this time interval (circles) compared against PISO‐1500 VADM stack (brown line). The black line represents the cumulative PDF curve for all lava flow data (Coe et al, ; Singer et al, ). (bottom) Astrochronologically tuned sediment cores ODP site 984 (Channell et al, ), with average sedimentation rate 11.5 cm kyr −1 ; IODP site U1308 (Channell et al, ), with average sedimentation rate 7.3 cm kyr −1 ); and MD90–961 (Channell et al, ), with average sedimentation rate 4.7 cm kyr −1 .…”

Section: Discussionmentioning

confidence: 99%

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Millennial‐Scale Instability in the Geomagnetic Field Prior to the Matuyama‐Brunhes Reversal

Balbas

Koppers

Clark

et al. 2018

Geochem Geophys Geosyst

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Changes in the Earth's magnetic field have global significance that reach from the outer core extending out to the uppermost atmosphere. Paleomagnetic records derived from sedimentary and volcanic sequences provide important insights into the geodynamo processes that govern the largest geomagnetic changes (polarity reversals), but dating uncertainties have hindered progress in this understanding. Here, we report a paleomagnetic record from multiple lava flows on Tahiti that bracket the Matuyama‐Brunhes (M‐B) polarity reversal ∼771,000 years ago. Our high‐precision 40Ar/39Ar ages constrain several rapid and short‐lived changes in field orientation up to 33,000 years prior to the M‐B reversal. These changes are similar to ones identified in other less well‐dated lava flows in Maui, Chile, and La Palma that occurred during an extended period of reduced field strength recorded in sediments. We use a simple stochastic model to show that these rapid polarity changes are highly attenuated in sediment records with low sedimentation rates. This prolonged 33,000 year period of reduced field strength and increased geomagnetic instability supports models that show frequent centennial‐to‐millennial‐scale polarity changes in the presence of a strongly weakened dipole field.

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“…This type of observation made on sedimentary sequences has been viewed with scepticism by some authors (Barton & McFadden 1995;Quidelleur et al 1995), who claim that the phenomenon is an artefact of the magnetization process in those rocks. However, some volcanic rocks also show geographical VGP confinement, as pointed out by Love (1998), Valet & Herrero-Bervera (2003), Coe & Glen (2004), and others.…”

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Characteristic wavelengths in VGP trajectories from magnetostratigraphic data of the Early Cretaceous Serra Geral lava piles, southern Brazil

Caminha-Maciel

Ernesto

2013

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The virtual geomagnetic pole (VGP) trajectories during some geomagnetic polarity reversals of different ages are marked by anisotropic behaviour. This recurrent phenomenon may be reflected in the paleomagnetic data, even if the transitional field was not completely recorded. As the long-scale geomagnetic variations have a confined oscillatory character, the VGP paths from stratigraphically controlled sequences may be described on the basis of sine and cosine functions, even if time is not the independent variable. Here we considered longitude (or space) as the independent variable which had to be 'unrolled' to overcome the 3608 repetitions as the VGPs moved around the geographic pole.Sixteen VGP series from the Early Cretaceous Serra Geral lava flows of southern Brazil were analysed using a modified version of the periodogram for uneven data series, and a combination of information approach. The combination of all the spectra, as in a stacking procedure, reduces noise and results in a smooth curve highlighting features of interest. We found a set of highest correlation wavelengths of approximately 167, 190, 209, 257, 277 and 3688. Phase analyses using two different methods revealed strikingly good coherence for some of these wavelengths, indicating that they are not only artefacts of the spectral analysis. Similar analysis of magnetostratigraphic data from the Icelandic Magmatic Province indicated that the two datasets may have wavelengths of approximately 165 and 2708 in common. These results suggest quasi-periodic behaviour, possibly with sub-harmonic instabilities owing to the modulating effect of inner Earth's anisotropies influencing the pole trajectory.

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The Complexity of Reversals

Abstract: Plate 1. Space-time variation of VGP latitude through the reversal from the same geodynamo simulation as in Figure 7. Time steps along the abscissa are 95 yr (38 kyr total). See text for discussion.

Cited by 13 publications

References 46 publications

GEOMAGIA50.v3: 2. A new paleomagnetic database for lake and marine sediments

GEOMAGIA50.v3: 2. A new paleomagnetic database for lake and marine sediments

Millennial‐Scale Instability in the Geomagnetic Field Prior to the Matuyama‐Brunhes Reversal

Characteristic wavelengths in VGP trajectories from magnetostratigraphic data of the Early Cretaceous Serra Geral lava piles, southern Brazil

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