Multi-process generated sediment waves on the Landes Plateau (Bay of Biscay, North Atlantic) Jean-Claude Fauge 'res a ;  , Eliane Gonthier a , Thierry Mulder a , Neil Kenyon b , Pierre Cirac a , Roger Griboulard a , Serge Berne ¤ c , Raymond Lesuave ¤ c a De ¤partement de Ge ¤ologie et Oce ¤anographie, UMR CNRS 5805-EPOC, 33405 Talence cedex, France b Southampton Oceanography Centre, Southampton SO14 3ZH, UK c DRO/GM, IFREMER, B.P. 70, 29280 Plouzane ¤, France Received 1 February 2001; accepted 31 July 2001 Abstract Detailed analyses of recently collected bathymetric and sparker seismic data, support a new interpretation of the Landes Plateau field of sediment waves located on the Aquitaine upper continental slope (Bay of Biscay). The wave geometry, previously described as the result of a major sediment failure, is interpreted as a structure with a complex origin including the interaction of depositional and gravity deformation processes. Depositional processes are mainly recorded by the upslope migrating pattern of the waves resulting from oblique or sigmoid downlap reflections on the upslope flank of the waves and by toplapping and truncated reflections on the downslope flank. Hemipelagic and turbiditic sedimentation may be involved in the wave building as well as contouritic processes that could be related to the existing northward polar current and internal waves. Gravity deformations are syndepositional, discontinuous and of low amplitude, affecting thick layers which alternate with undeformed layers. They seem to correspond to gentle sediment creeping or stretching associated with minor listric or compaction-like faults, and possible limited back rotation of sediment blocks. These multi-process generated sediment waves could be rather common on the continental margins as they could have been mistaken with either depositional or deformational structures. ß 2002 Elsevier Science B.V. All rights reserved. Keywords: continental slope; Bay of Biscay; Landes Plateau; sediment wave; process interaction; sediment deformation; contour current; seismic data 1. Introduction Sediment waves are usually giant bedforms commonly observed on the sea£oor from the shelf break to the abyssal domains of the deep ocean. They form mainly in ¢ne-grained sediment (clays and silts) and occur regularly over large areas. Their dimensions range from tens to about one hundred metres in amplitude and hundreds of metres to kilometres in wavelength. Three di¡er- ent types of processes are usually evoked as re- sponsible for the settling of such sediment waves (Fauge 'res et al., 1999): turbidity-current process, 0025-3227/02/$ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII:S0025-3227(01)00242-0 * Corresponding author. Tel.: +33-5684-8853; Fax: +33-5684-0848. E-mail address: faugeres@geocean.u-bordeaux.fr (J.-C. Fauge 'res). Marine Geology 182 (2002) 279^302 www.elsevier.com/locate/margeo