Giant seabed polygons and underlying polygonal faults in the Caribbean Sea as markers of the sedimentary cover extension in the Grenada Basin
|Acceptance Date||2021 IN PRESS|
|Author(s)||Gay Aurelien1, Padron Mora Crelia2, 3, Meyer Solene1, 4, Beaufort Daniel5, Oliot Emilien1, Lallemand Serge E1, Marcaillou Boris4, Philippon Mélody1, Cornée Jean-Jacques1, Audemard Franck A6, Lebrun Jean-Frédéric1, Klingelhoefer Frauke3, Mercier De Lepinay Bernard4, Munch Philippe1, Garrocq Clément1, Boucart Milton1, 4, Laigle Mireille4, Schenini Laure4, The Garanti Cruise Team|
|Affiliation(s)||1 : Géosciences Montpellier, CNRS, Université de Montpellier, Université des Antilles, Place Eugène 1Bataillon, 34095 Montpellier, France
2 : Departamento de Ciencias de la Tierra, Universidad Simón Bolívar (USB), Caracas, Venezuela.
3 : Géosciences Marines, Ifremer, ZI de la Pointe du Diable, CS 10070, 29280 Plouzané, France
4 : Géoazur, Université Côte d’Azur, CNRS, IRD, Observatoire de la Côte d’Azur, Géoazur, 250 Avenue Albert Einstein, 06560 Valbonne, France
5 : Université de Poitiers, IC2MP - UMR 7285 - CNRS, Rue Michel Brunet, F-86073 Poitiers cedex 9, France
6 : Universidad Nacional de San Luis, San Luis, Argentina
|Source||Earth and Space Science Open Archive (Wiley) In Press|
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.