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Giant seabed polygons and underlying polygonal faults in the Caribbean Sea as markers of the sedimentary cover extension in the Grenada Basin
  • +15
  • Aurelien Gay,
  • Crelia Padron,
  • Solene Meyer,
  • Daniel Beaufort,
  • Émilien Oliot,
  • Serge E. Lallemand,
  • Boris Marcaillou,
  • Mélody Philippon,
  • Jean-Jacques Cornée,
  • Franck A. Audemard,
  • Jean-Frédéric Lebrun,
  • Frauke Klingelhoefer,
  • Bernard Mercier de Lepinay,
  • Philippe Munch,
  • Clément Garrocq,
  • Milton Boucart,
  • Mireille Laigle,
  • Laure Schenini
Aurelien Gay
Université de Montpellier, Université des Antilles

Corresponding Author:aurelien.gay@umontpellier.fr

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Crelia Padron
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Solene Meyer
University of Montpellier
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Daniel Beaufort
Université de Poitiers
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Émilien Oliot
UMR 5243 Géosciences Montpellier, CNRS, Université de Montpellier, 34095, Montpellier Cedex 05, France
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Serge E. Lallemand
CNRS, Universite Montpellier
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Boris Marcaillou
Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, IRD, Geoazur
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Mélody Philippon
Géosciences Montpellier
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Jean-Jacques Cornée
University of Montpellier, France
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Franck A. Audemard
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Jean-Frédéric Lebrun
Université des Antilles
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Frauke Klingelhoefer
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Bernard Mercier de Lepinay
CNRS Université Côte d'Azur
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Philippe Munch
Geosciences Montpellier
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Clément Garrocq
Géosciences Montpellier
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Milton Boucart
Université Côte d'Azur
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Mireille Laigle
Université Nice Sophia Antipolis
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Laure Schenini
Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, IRD, Géoazur, v
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Based on an extensive seismic and multibeam dataset, 1-5 km wide giant polygons were identified at the bottom of the Grenada basin, covering a total area of ~55000 km². They represent the top part of an active underlying polygonal fault system due to the volumetric contraction of clay- and smectite-rich sediments during burial. To date, this is the widest area of outcropping polygonal faults ever found on Earth. The seabed polygons are bounded by rectilinear ~1000-1500 m wide and ~10-60 m deep furrows, depending on the location in the basin. They are relatively regular in the north Grenada Basin, whereas they are getting longer and more elongated in the south Grenada Basin. The polygonal faults consist in a set of discrete normal faults affecting a 700 to 1200 m thick interval, initiated in the shallow sub-surface at the transition between Early to Middle Pliocene and then having propagated both upward and downward during sedimentation. The centre-to-centre method has been applied to determine the local ellipse of strains, providing a major orientation for extension needed for polygons to initiate. In the north, the minor axes are oriented N40°, indicating a general NE-SW extension of the upper part of the sedimentary cover consistent with the forearc/backarc regional extension. In the south Grenada Basin, minor axes are progressively turning towards the south, pointing out the actual maximum subsidence point. This implies that seabed polygonal faults could thus be indicative of the present-day (or recent) strain state within the upper sedimentary column.