scholarly journals Investigation of a marine magnetic polarity reversal boundary in cross section at the northern boundary of the Kane Megamullion, Mid-Atlantic Ridge, 23°40′N

2016 ◽  
Vol 121 (5) ◽  
pp. 3161-3176 ◽  
Author(s):  
Min Xu ◽  
M. A. Tivey
Keyword(s):  
Cross Section ◽  
Magnetic Polarity ◽  
Polarity Reversal ◽  
Northern Boundary ◽  
Mid Atlantic Ridge ◽  
Magnetic Polarity Reversal

Davis Creek silt, an Early Pleistocene or Late Pliocene deposit in the Cypress Hills of Saskatchewan

1989 ◽  
Vol 26 (1) ◽  
pp. 192-198 ◽  
Author(s):  
W. J. Vreeken ◽  
R. W. Klassen ◽  
R. W. Barendregt
Keyword(s):  
Volcanic Ash ◽  
Magnetic Polarity ◽  
Polarity Reversal ◽  
Early Pleistocene ◽  
The South ◽  
Glacial Deposits ◽  
Late Pliocene ◽  
Late Wisconsinan ◽  
Weathering Zone ◽  
Magnetic Polarity Reversal

Davis Creek silt is the informal name for a previously unreported loess and its reworked detritus encountered at several locations to the south of the east and centre blocks of the Cypress Hills. This unit intervenes between a pediment with an estimated age of 10 Ma and Late Wisconsinan glacial deposits. Because the unit has reversed magnetization, it is older than 788 ka, the astronomical age of the Matuyama–Brunhes magnetic polarity reversal. The unit also contains an undated volcanic ash from the Pearlette ash family that could represent the Mesa Falls (1.27 Ma) or the Huckleberry Ridge (2.02 Ma) ash bed. Davis Creek silt overlies an oxidized weathering zone and contains large secondary carbonate nodules near its truncated top that were, in places, reworked into a lag deposit or stone line before accumulation of the glacial overburden. At one location Davis Creek silt is separated from this overburden by a unit of cryoturbated gravelly loam with remnants of a reddish-yellow paleosolic B horizon.

scholarly journals Magnetic cycles of the planet-hosting star τ Bootis - II. A second magnetic polarity reversal

2009 ◽  
Vol 398 (3) ◽  
pp. 1383-1391 ◽  
Author(s):  
R. Fares ◽  
J.-F. Donati ◽  
C. Moutou ◽  
D. Bohlender ◽  
C. Catala ◽  
...  
Keyword(s):  
Magnetic Polarity ◽  
Polarity Reversal ◽  
Magnetic Cycles ◽  
Magnetic Polarity Reversal

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.

Timing of the Brunhes-Matuyama magnetic polarity reversal in Chinese loess using 10Be

Geology ◽  
2014 ◽  
Vol 42 (6) ◽  
pp. 467-470 ◽  
Author(s):  
Weijian Zhou ◽  
J. Warren Beck ◽  
Xianghui Kong ◽  
Zhisheng An ◽  
Xiaoke Qiang ◽  
...  
Keyword(s):  
Magnetic Polarity ◽  
Polarity Reversal ◽  
Chinese Loess ◽  
Magnetic Polarity Reversal

scholarly journals Synchronizing volcanic, sedimentary, and ice core records of Earth’s last magnetic polarity reversal

2019 ◽  
Vol 5 (8) ◽  
pp. eaaw4621 ◽  
Author(s):  
Brad S. Singer ◽  
Brian R. Jicha ◽  
Nobutatsu Mochizuki ◽  
Robert S. Coe
Keyword(s):  
Magnetic Field ◽  
Short Duration ◽  
Ice Core ◽  
Magnetic Polarity ◽  
Lava Flows ◽  
Polarity Reversal ◽  
Field Polarity ◽  
Reversal Process ◽  
Complex Process ◽  
Magnetic Polarity Reversal

Reversal of Earth’s magnetic field polarity every 105 to 106 years is among the most far-reaching, yet enigmatic, geophysical phenomena. The short duration of reversals make precise temporal records of past magnetic field behavior paramount to understanding the processes that produce them. We correlate new 40Ar/39Ar dates from transitionally magnetized lava flows to astronomically dated sediment and ice records to map the evolution of Earth’s last reversal. The final 180° polarity reversal at ~773 ka culminates a complex process beginning at ~795 ka with weakening of the field, succeeded by increased field intensity manifested in sediments and ice, and then by an excursion and weakening of intensity at ~784 ka that heralds a >10 ka period wherein sediments record highly variable directions. The 22 ka evolution of this reversal suggested by our findings is mirrored by a numerical geodynamo simulation that may capture much of the naturally observed reversal process.

Energy Transmission by Barotropic Rossby Waves Revisited

2005 ◽  
Vol 35 (11) ◽  
pp. 2228-2236 ◽  
Author(s):  
R. P. Matano ◽  
E. D. Palma
Keyword(s):  
Cross Section ◽  
Rossby Waves ◽  
Bottom Topography ◽  
Low Frequency ◽  
Energy Transmission ◽  
Low Pass ◽  
Mid Atlantic Ridge ◽  
High Frequency Waves ◽  
The Individual ◽  
Matching Techniques

Abstract This article presents a semianalytic method to investigate the properties of energy transmission across bottom topography by barotropic Rossby waves. The method is first used to revisit the analytical estimates derived from wave-matching techniques and Wentzel–Kramers–Brillouin (WKB) approximations. The comparison between the semianalytic method and WKB indicates that the results of the latter are valid for waves with periods longer than a month and ridges taller than ∼1000 m and wider than ∼500 km. For these parameter values both methods predict the passage of low-frequency waves and the reflection of high-frequency waves. The semianalytic method is then used to discuss the energy transmission properties of a cross section of the Mid-Atlantic Ridge. It is shown that the filtering characteristics of realistic bottom topographies depend not only on the spatial scale set by the cross-section envelope, but also on the scales of the individual peaks. This dependence is related to the fact that topographies narrower than ∼400 km (e.g., peaks) are high-pass filters of incoming waves, while topographies wider than that (e.g., cross-section envelopes) are low-pass filters. In the particular case of the Mid-Atlantic Ridge the neglect of the contribution of individual peaks leads to an erroneous estimate of the filtering properties of the massif.

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