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Magnetic Mineralogy and Paleomagnetic Record of the Nama Group, Namibia: Implications for Large-Scale Remagnetization of West Gondwanaland and Ediacaran Geomagnetic Instability
  • +3
  • Thales Pescarini,
  • Ricardo IF Trindade,
  • David A.D. Evans,
  • Joseph L. Kirschvink,
  • James Pierce,
  • Henrique Albuquerque Fernandes
Thales Pescarini
University of Sao Paulo

Corresponding Author:[email protected]

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Ricardo IF Trindade
Universidade de Sao Paulo
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David A.D. Evans
Yale University
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Joseph L. Kirschvink
California Institute of Technology
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James Pierce
Yale University
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Henrique Albuquerque Fernandes
University of São Paulo
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Abstract

The late Ediacaran to early Cambrian was marked by significant biological and geochemical transformations, including the diversification of animal life, and an enigmatic paleomagnetic record. This study focuses on the Nama Group, a key geological unit for understanding the Ediacaran-Cambrian transition, yet hampered by limited paleogeographic constraints. Previous paleomagnetic studies identified complex remagnetization patterns but lacked a detailed examination of remanence carriers. To address this, we conducted field stability tests and employed advanced rock magnetic techniques on unweathered borehole core samples to complement paleomagnetic data. Thermal demagnetization identified three magnetic components. C1 is a present-day field viscous remanent magnetization (VRM) and was used for borehole core orientation. C2, carried by single domain (SD) pyrrhotite and SD magnetite, aligns with early Paleozoic remagnetization poles from West Gondwanaland and was likely acquired through a thermoviscous magnetization (TVRM) in magnetite and a thermoremanent magnetization (TRM) in pyrrhotite, suggesting regional uplift and cooling between 500-480 Ma. This quasi-synchronous remagnetization is supported by highly clustered paleomagnetic poles and thermochronological data. C3 is an anomalous component with significant inclination variation within the stratigraphy, carried by large pseudo-single domain (PSD) magnetites, possibly of primary, detrital origin. The pattern resembles findings from other cratons, suggesting an unstable geomagnetic field that could have persisted until ca. 540 Ma. This may represent one of the youngest occurrences of such extreme geomagnetic instability in the Ediacaran and provides the first evidence of this behavior in the Kalahari Craton, adding new support for a largely unstable geomagnetic field during this period.
29 Oct 2024Submitted to ESS Open Archive
30 Oct 2024Published in ESS Open Archive