Multi-process generated sediment waves on the Landes Plateau (Bay of Biscay, North Atlantic)

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. (C) 2002 Elsevier Science B.V. All rights reserved.