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The strength of the Earth’s magnetic field and the Cretaceous Normal Superchron: New data from Costa Rica
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  • Anita Di Chiara,
  • Lisa Tauxe,
  • Fabio Florindo,
  • Staudigel Hubert,
  • Marino Protti,
  • Yongjae Yu,
  • Jo-Anne Wartho,
  • Paul Paul van den Bogaard,
  • Kaj Hoernle
Anita Di Chiara
Istituto Nazionale di Geofisica e Vulcanologia

Corresponding Author:[email protected]

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Lisa Tauxe
University of California, San Diego
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Fabio Florindo
Istituto Nazionale di Geofisica e Vulcanologia
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Staudigel Hubert
Scripps Institution of Oceanography
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Marino Protti
Observatorio Vulcanológico y Sismológico de Costa Rica
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Yongjae Yu
Chungnam National University
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Jo-Anne Wartho
GEOMAR Helmholtz Centre for Ocean Research Kiel
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Paul Paul van den Bogaard
GEOMAR Helmholtz Centre for Ocean Research Kiel
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Kaj Hoernle
GEOMAR Helmholtz Center for Ocean Research Kiel
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Abstract

Constraining the long-term variability and average of the Earth’s magnetic field strength is fundamental to understanding the characteristics and behavior of the geomagnetic field. Questions remain about the strength of the average field, and the rela-tionship between strength and reversal frequency. The dispersion of data from key timeintervals reflects the complexity in obtaining absolute paleointensity values. Here, we focus on the Cretaceous Normal Superchron (CNS; 121-84 Ma), during which there were no reversals. We present new results from 42 submarine basaltic glass (SBG) sites collected on the Nicoya Peninsula and Murcielago Islands, Costa Rica and new and revised 40Ar/39Ar ages along with biostratigraphic age constraints from previous studies that indicate ages from 141 to 112 Ma. One site with a 40Ar/39Ar age of 135+\-1.5Ma (2σ) gave a reliable intensity result of 34+\-μT (equivalent to a paleomagnetic dipole moment, PDM, value of 88+\-20 ZAm2), while three sites between 121 and 112 vary from 21+\- to 34+\-4 μT (53+\-3 to 87+\-10 ZAm2) spanning the onset of the CNS. These results from the CNS are all higher than the long-term average of ~42 ZAm2 and similar to data from Suhongtu (46-53 ZAm2) and the Troodos Ophiolite (81 ZAm2, reinterpreted, using the same criteria of this study). Together with the reinterpreted data, the new Costa Rica results suggest thatthe strength of the geomagnetic field was about the same before and after the onset ofthe CNS. Therefore, the data do not support a strict correlation between polarity interval length and the strength of the magnetic field.
Apr 2021Published in Geochemistry, Geophysics, Geosystems volume 22 issue 4. 10.1029/2020GC009605