Slope instabilities from echo-character mapping along the French Guiana transform margin and Demerara abyssal plain

Type Article
Date 2009-05
Language English
Author(s) Loncke L.1, Droz Laurence2, Gaullier V.1, Basile C.3, Patriat MartinORCID4, Roest WalterORCID4
Affiliation(s) 1 : Univ Perpignan, Lab IMAGES, F-66860 Perpignan, France.
2 : Inst Univ Europeen Mer, CNRS, UMR 6538, F-29280 Plouzane, France.
3 : Univ Grenoble 1, CNRS, UMR 5025,Observ Sci Univers Grenoble, Lab Geodynam Chaines Alpines, F-38400 St Martin Dheres, France.
4 : IFREMER, DRO GM Geosci Marines, F-29280 Plouzane, France.
Source Marine and Petroleum Geology (0264-8172) (Elsevier), 2009-05 , Vol. 26 , N. 5 , P. 711-723
DOI 10.1016/j.marpetgeo.2008.02.010
WOS© Times Cited 30
Keyword(s) Structural heritage, Fluids, Creeping, Transform margin, Slope instabilities
Abstract The French Guiana transform margin and Demerara abyssal plain have been recently surveyed in the framework of the EXTRAPLAC French Program of extension of the continental shelf (Guyaplac survey, Ifremer-IFP-SHOM-IPEV). Based on the interpretation of some of the data collected during the Guyaplac survey (Simrad-EM12 multibeam bathymetric data, backscatter imagery, and 3.5 kHz profiles), the area can be divided into three morphostructural domains. (1) The western Guiana margin, including a part of the Demerara plateau, an important bathymetric relief prolonging the continental platform off Guiana and Surinam. This domain is bounded by (1a) the NWSE trending northern border of the Demerara plateau which appears quite steep and corresponds to a transform segment of the margin, (1b) the N-S eastern border of the Demerara plateau which corresponds to a divergent segment of the margin. The Demerara plateau shows a segmented morphology, low slope gradients, and a very rough surface (ripples perpendicular to the slope direction). NNW-SSE structural steps seem to correspond to collapses of 100 km long blocs towards the east. Slumps initiate along these directions. The observed rough bathymetry seems to be related to creeping processes. At a greater scale (seismic data), this part of the margin has been totally destabilized (numerous imbricate transparent masses rooted at about 0.5 s.t.w.t.t. below seafloor). The NW-SE trending northern border of the Demerara plateau corresponds to a cliff-like continental slope, probably slightly smoother than other transform margins (Ghana/cote d'Ivoire margin). The N-S eastern border of Demerara plateau is characterized by numerous small-scale imbricate slumps. Some of these failures seem to be emplaced in the prolongation of the NNW-SSE structural steps identified on the Demerara plateau. (2) The eastern Guiana margin corresponds to a NW-SE oriented gullied transform margin segment. The associated continental slope is very steep and characterized by numerous imbricate slumps and related debris flows. Some undulated masses, probably corresponding to creeping sediments or to older mass-wasting events are still imprinted on bathymetry. This transform margin segment is nearly entirely destabilized and eroded. (3) The Demerara abyssal plain. This domain is characterized eastwards by channels belonging to the Amazon turbidite system and westwards, at the foot of Demerara continental slope, by sediment waves probably created by contour currents. To conclude, it seems that there is a strong relationship between the structure (transform and divergent segments) and the emplacement of recurrent slope instabilities. These are probably related to the steepness of the slopes but also to subsidence histories generating in some cases huge deep-seated collapses of the whole margin. Fluid ascents are common everywhere in the area, probably enhancing slope instability. Their origin is not constrained but the black shales or Cretaceous organic-rich layers could be good candidates.
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