scholarly journals Steady increase in geomagnetic reversal frequency after the Cretaceous Normal Superchron

2022 ◽  
Author(s):  
Yutaka Yoshimura ◽  
Osamu Ishizuka ◽  
Toshitsugu Yamazaki ◽  
Yuhji Yamamoto ◽  
Hyeon-Seon Ahn ◽  
...  
Keyword(s):  
Heat Flux ◽  
Mantle Convection ◽  
Steady Increase ◽  
Geomagnetic Reversal ◽  
Core Mantle Boundary ◽  
The Core ◽  
Marine Magnetic Anomalies ◽  
Reversal Frequency ◽  
Geomagnetic Polarity ◽  
Geomagnetic Polarity Time Scale

Abstract The Earth's core is constantly and efficiently cooled by mantle convection. The heat flux transferred from the core to the mantle through the core-mantle boundary (CMB) is critical for understanding the dynamics of solid Earth. Although it is difficult to estimate the CMB heat flux, its history could be reconstructed from geomagnetic reversal frequency. However, overlooked short geomagnetic reversals may exist in the geomagnetic polarity time scale (GPTS), which affects the estimation of the heat flux history. Here, we report four new high-precision 40Ar/39Ar ages of the Oligocene Ethiopian traps. The traps may contain undiscovered reversals in marine magnetic anomaly. Based on the ages, we identified new reversals in Chron C12n, which was not found in marine magnetic anomalies. Our non-parametric analysis of GPTS suggests four potential periods of missing geomagnetic reversals, which correspond to long polarity intervals in GPTS. We found that C12n correspond to one of the periods. This indicates that several undetected reversals may exist within or near the edge of long polarity intervals after the Cretaceous Normal Superchron (prolonged stable polarity period). Considering the undetected reversals, we conclude that the CMB heat flux increased more slowly and monotonically after the Superchron than that ever estimated.

Devonian magnetostratigraphy: new data and old problems

2021 ◽  
Author(s):  
Annique van der Boon ◽  
Andy Biggin ◽  
Daniele Thallner ◽  
Mark Hounslow ◽  
Jerzy Nawrocki ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Time Scale ◽  
Age Determination ◽  
Paleomagnetic Data ◽  
Show Evidence ◽  
Reversal Frequency ◽  
Geomagnetic Polarity ◽  
Geomagnetic Polarity Time Scale

<p>The global polarity time scale (GPTS) is relatively unconstrained for the Paleozoic, particularly the Devonian. Constraining the GPTS and reversal frequency for the Devonian is crucial for the understanding of the behaviour of Earth’s magnetic field. Furthermore, construction of a GPTS for the Paleozoic could provide a valuable tool for age determination in other studies. However, most paleomagnetic data from the Devonian is problematic. The data are difficult to interpret and don’t have a single easy to resolve (partial or full) overprint. Paleointensity studies suggest that the field was much weaker than the field of today, which could have been accompanied by many reversals (a hyperreversing field). In order to improve the geomagnetic polarity time scale in the Devonian, and quantify the number of reversals in this time, we sampled three Devonian sections in Germany, Poland and Canada. These sections show evidence that the rocks were not significantly heated, and they show little evidence for remineralisation. This minimises the chance the rocks were remagnetised after the Devonian. Our data show that even when rocks are well qualified to have reliably recorded the Devonian field, the interpretation is not straightforward. We also discuss problems with the Devonian GPTS as presented in the geologic timescale.</p>

scholarly journals Mantle convection behavior with segregation in the core-mantle boundary

1996 ◽  
Vol 23 (16) ◽  
pp. 2061-2064 ◽  
Author(s):  
Günter Nauheimer ◽  
Anatoly S. Fradkov ◽  
Horst J. Neugebauer
Keyword(s):  
Mantle Convection ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core

scholarly journals A coupled core-mantle evolution: review and future prospects

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Takashi Nakagawa
Keyword(s):  
Inner Core ◽  
Future Prospects ◽  
Core Mantle Boundary ◽  
Mantle Evolution ◽  
The Core ◽  
Secular Variations ◽  
Onset Timing ◽  
Polarity Reversals ◽  
Geomagnetic Polarity

Abstract In this review, I provide the current status and future prospects for the coupled core-mantle evolution and specifically summarize the constraints arising from geomagnetism and paleomagnetism on the long-term secular variations of the geomagnetic field. The heat flow across the core-mantle boundary (CMB) is essential for determining the best-fit scenario that explains the observational data of geomagnetic secular variations (e.g., onset timing of the inner core growth, geomagnetic polarity reversals, and westward drift) and should include the various origins of the heterogeneous structures in the deep mantle that have affected the heat transfer across the core-mantle boundary for billions of years. The coupled core-mantle evolution model can potentially explain the onset timing of the inner core and its influence on the long-term geomagnetic secular variations, but it is still controversial among modeling approaches on the core energetics because the paleomagnetic data contains various uncertainties. Additionally, with the coupled core-mantle evolution model in geodynamo simulations, the frequency of the geomagnetic polarity reversals can be explained with the time variations of the heat flow across the CMB. Additionally, the effects of the stable region in the outermost outer core to the magnetic evolution are also crucial but there would be still uncertain for their feasibility. However, despite this progress in understanding the observational data for geomagnetic secular variations, there are several unresolved issues that should be addressed in future investigations: (1) initial conditions—starting with the solidification of the global magma ocean with the onset timing of plate tectonics and geodynamo actions and (2) planetary habitability—how the dynamics of the Earth’s deep interior affects the long-term surface environment change that has been maintained in the Earth’s multisphere coupled system.

A revised magnetic polarity timescale for the Cretaceous and Cainozoic

1982 ◽  
Vol 306 (1492) ◽  
pp. 129-136 ◽  
Keyword(s):  
Magnetic Polarity ◽  
Geomagnetic Reversal ◽  
Sea Floor ◽  
Marine Magnetic Anomalies ◽  
Increasing Trend ◽  
Reversal Frequency ◽  
Spreading Rates ◽  
Sea Floor Spreading ◽  
Central Atlantic ◽  
Stage Boundaries

Magnetostratigraphic correlations of biostratigraphic stage boundaries have established calibration points for dating the polarity reversal sequence derived from marine magnetic anomalies. Interpolation between the best-estimate ages for these tie points gives a revised magnetic polarity timescale for the Cainozoic and Cretaceous. Recomputed sea-floor spreading rates for this time prove to be high during the Cretaceous quiet interval at several plate margins, but remained remarkably constant in the central Atlantic. The geomagnetic reversal frequency, when averaged over intervals of several megayears duration, has exhibited a steadily increasing trend since the late Cretaceous.

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