The Cretaceous Normal Superchron: A Mini-Review of Its Discovery, Short Reversal Events, Paleointensity, Paleosecular Variations, Paleoenvironment, Volcanism, and Mechanism

Yoshimura, Y

doi:10.3389/feart.2022.834024

Cited by 7 publications

(3 citation statements)

References 99 publications

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“…Geomagnetic polarity during the CNS was oriented in normal direction (Ogg, 2020), even though short reversal events may have existed (Yoshimura, 2022). Hence, the presence of remanent magnetization in our study area would amplify the magnetic signal in the same direction.…”

Section: High Magnetization In the Lower Crustmentioning

confidence: 85%

Increased metamorphic conditions in the lower crust during oceanic transform fault evolution

Haas,

Thomas,

Heine

et al. 2024

Preprint

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Abstract. Oceanic transform faults connect the segments of active spreading ridges that slide past each other. In a classical view, transform faults are considered as conservative, where no material is added or destroyed. Recent studies, however, suggest that the crust in the transform fault region is deformed during different episodes. We combine high resolution 3D broadband seismic data with shipborne potential field data to study ancient fault zones in Albian-Aptian aged oceanic crust in the eastern Gulf of Guinea offshore São Tomé and Príncipe. The crust in this region is characterized by a thin, high-reflective upper crust, which is underlain by a thick, almost seismically transparent unit that comprises localized dipping reflectors, previously interpreted as extrusive lava flows. This layer defines the target area for inversion and forward modelling of the potential field data. The picked seismic horizons are used as geometrical boundaries of the crustal model. First, we perform a lateral parameter inversion for the lower crust, which provides vertical columns of density and magnetic susceptibility. Second, we sort the estimated values using a clustering approach and identify five groups with common parameter relationships. Third, we use the clustered lower crustal domains to define a consistent 3D model of the study area that aligns with the seismic structure and geological concepts, preferred to the simple inversion of the first step. The final model shows anomalous low susceptibility and medium to high density close to the buried fracture zones, which reflects increasing pressure and temperature conditions accompanied by a change of metamorphic facies. Our model indicates enhanced tectonic activity with an extensional component during the formation of oceanic crust that culminates in the transform region. These results are in line with recent studies and strengthen the impressions of a non-conservative character of ridge-transform intersections.

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Section: High Magnetization In the Lower Crustmentioning

confidence: 85%

Increased metamorphic conditions in the lower crust during oceanic transform fault evolution

Haas,

Thomas,

Heine

et al. 2024

Preprint

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“…The long CNS lasted ~37 Myr, ending at about 83 Myr (He et al 2012). Some brief reversed polarity intervals may exist at the end of the CNS but have yet to be confirmed worldwide (Yoshimura 2022).…”

Section: Discussionmentioning

confidence: 99%

The Late Cretaceous alkaline magmatism in the SE Brazilian coast: new paleomagnetic data and age constraints

Ernesto

Raposo²

2023

Braz. J. Geol.

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Alkaline dikes from the Santos-Rio de Janeiro coast, SE Brazil, mainly from São Sebastião and Búzios islands, yielded a Late Cretaceous paleomagnetic pole (SR) located at 319.7°E 81.2°S (N = 44, A 95 = 3.0°, k = 44). This pole includes some sites of alkaline stocks from São Sebastião Island of the same age and supersedes the previous pole for this island. To match the available radiometric ages and the prevailing normal polarity remanence of the rocks with the geomagnetic polarity time scale, the SR pole is placed at 84 Myr. Another group of alkaline rocks, dikes located mainly in Rio de Janeiro, was assigned an age of less than 70 Myr. The ages of the Poços de Caldas, Itatiaia, and Passa Quatro paleomagnetic poles are also discussed based on available radiometric data. Assuming a rigid plate, the SR pole indicates the southward movement of about 7° with virtually no rotation between 100 and 84 Myr. From approximately 84 to 70 Myr, a clockwise rotation of 8° is postulated, with slight variation in latitude.

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“…Since different geomagnetic field behaviors entail different geodynamo processes, the nature of the geodynamo during superchrons remain elusive as well. The Cretaceous Normal Superchron (CNS, ∼121 Ma to ∼84 Ma), which exhibits an almost uniform normal polarity for nearly 40 Myrs, offers a prime example to unravel the enigma of the geodynamo during a superchron (e.g., Yoshimura, 2022). Also, during the CNS, extensive formation of large igneous provinces (LIPs), widespread ocean anoxia, multiple biotic turnovers and large global carbon perturbations occurred (Jenkyns, 2010; Larson, 1991; Leckie et al., 2002), indicating an interval of upheaval of the entire Earth system from its interior (geodynamo) to surficial processes (marine environmental changes).…”

Section: Introductionmentioning

confidence: 99%

Salient Changes of Earth's Magnetic Field Toward the End of Cretaceous Normal Superchron (CNS)

Liu,

Li,

Richter

2024

JGR Solid Earth

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Changes in Earth's magnetic field during the Cretaceous Normal Superchron (CNS) spanning ∼121 Ma to ∼84 Ma hold important clues about the geodynamo evolution. Canonical models predict a persistently strong geomagnetic field with low variability during CNS, which, however, has not been observed in the available absolute paleointensity data and seafloor marine magnetic anomaly (MMA) records. The lack of relative paleointensity (RPI) data across CNS further impedes tests of model predictions. Here, we present a ∼9‐Myr (∼94–∼85 Ma) RPI record from a Turonian to Santonian hemipelagic succession from IODP Site U1512 offshore southern Australia. Detailed paleomagnetic and rock magnetic analyses demonstrate that the ratio of natural remanent magnetization (NRM) demagnetized at 20 mT over magnetic susceptibility (MS), that is, NRM20mT/MS, as a reliable proxy for the RPI of the Upper Cretaceous succession. The new RPI record shows marked changes in both intensity and variability at ∼90.8 Ma. Also, the 6 Myr‐long (∼94–∼88 Ma), near‐continuous, ∼1.2 kyr‐resolution RPI record exhibits a strong positive correlation between field intensity and variability. Assuming this correlation holds for the entire CNS, an extrapolated RPI curve for the entire CNS is obtained by integrating the positive correlation with field variability estimates from the MMA data. The extrapolated RPI curve shows a strong and highly variable field in the middle CNS but a weak and stable field at its beginning and ending. These features imply a much more dynamic geodynamo than previously thought, and provide crucial benchmarks for unraveling the geodynamo evolution during CNS.

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The Cretaceous Normal Superchron: A Mini-Review of Its Discovery, Short Reversal Events, Paleointensity, Paleosecular Variations, Paleoenvironment, Volcanism, and Mechanism

Cited by 7 publications

References 99 publications

Increased metamorphic conditions in the lower crust during oceanic transform fault evolution

Increased metamorphic conditions in the lower crust during oceanic transform fault evolution

The Late Cretaceous alkaline magmatism in the SE Brazilian coast: new paleomagnetic data and age constraints

Salient Changes of Earth's Magnetic Field Toward the End of Cretaceous Normal Superchron (CNS)

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