Structure of the Demerara passive-transform margin and associated sedimentary processes. Initial results from the IGUANES cruise

L. Loncke 1 A. Maillard 2 C. Basile 3 R. Roest 4 G. Bayon 4 V. Gaullier 5 F. Pattier 1 M. Mercier de Lépinay 1 C. Grall 1 L. Droz 6 T. Marsset 4 P. Giresse 1 C. Caprais 4 C. Cathalot 4 D. Graindorge 6 A. Heuret 7 F. Lebrun 7 S. Bermell 4 B. Marcaillou 7 C. Sotin 1 B. Hebert 1 M. Patriat 4 M. Bassetti 1 C. Tallobre 1 R. Buscail 8 X. Durrieu de Madron 1 F. Bourrin 8
1 CEFREM - Centre de Formation et de Recherche sur les Environnements Méditérranéens
2 GET - Géosciences Environnement Toulouse
3 ISTerre - Institut des Sciences de la Terre
4 IFREMER - Institut Français de Recherche pour l'Exploitation de la Mer - Brest
5 Géosystèmes - CNRS UMR8217
6 LDO - Domaines Océaniques
7 LARGE - Laboratoire de Recherche en Géosciences et Energies
8 CEFREM - Centre de formation et de recherche sur l'environnement marin
Abstract : he IGUANES cruise took place in May 2013 on the R/V L'Atalante along the Demerara passive transform margin off French Guiana and Surinam. Seismic, multibeam and chirp acquisitions were made. Piston cores were collected for pore geochemistry and sedimentology. A mooring was deployed on the sea-bottom for 10 months (temperature, salinity, turbidity and current measurements). This new dataset highlights the lateral variability of the 350 km-long Guiana–Surinam transform margin due to the presence of a releasing bend between two transform segments. The adjacent Demerara Plateau is affected by a 350 km-long giant slide complex. This complex initiated in Cretaceous times and was regularly reactivated until recent times. Since the Miocene, contourite processes seem to be active due to the onset of the North Atlantic Deep Water (NADW) bottom current. A main NADW water vein flows towards SE, eroding slide headscarps and allowing the deposition of contourite drifts. Numerous depressions looking like comet tails or comet scours record this flow. Some of those were interpreted before the cruise as active pockmarks. Pore geochemistry and core analysis do not show any evidence of present-day gas seepage.
Keywords : demerara marginal Iguanes cruise sedimentology geochemistry
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Journal articles
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L. Loncke, A. Maillard, C. Basile, R. Roest, G. Bayon, et al.. Structure of the Demerara passive-transform margin and associated sedimentary processes. Initial results from the IGUANES cruise. The Geological Society, London, Special Publications, Geological Society of London, 2016, 431 (1), pp.179 - 197. ⟨10.1144/SP431.7⟩. ⟨hal-01741165⟩

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