CREO, Allée des Tamaris, 17000 La Rochelle, France.
Internal structure of subtidal sandwaves revealed by high-resolution seismic reflection
Version of Record online: 14 JUN 2006
Volume 35, Issue 1, pages 5–20, February 1988
How to Cite
BERNÉ, S., AUFFRET, J.-P. and WALKER, P. (1988), Internal structure of subtidal sandwaves revealed by high-resolution seismic reflection. Sedimentology, 35: 5–20. doi: 10.1111/j.1365-3091.1988.tb00902.x
- Issue online: 14 JUN 2006
- Version of Record online: 14 JUN 2006
- 10 February 1987 revision 4 June 1987
Bedforms of the Surtainville area, off the Cherbourg peninsula, include subtidal sandwaves, which are a good example of mega-structures associated with the strong tidal currents prevailing in the English Channel. A fine-scale study using a high-accuracy echo-sounder and side-scan sonar shows that some of these sandwaves have a crescentic shape and a strong asymmetry indicating a sand movement toward the north. The sandwaves range in height from about 3.5 m to 7.5 m, in width from 100 m to 500 m and in length from 70 m to 200 m; their internal structure, revealed by the simultaneous use of a high-resolution seismic source, is characterized by large ‘foreset’ beds dipping in the same direction as the lee sides of the sandwaves. Groups of foresets are limited by reactivation surfaces which we interpret as erosional surfaces created by subordinate tides. The presence of horizontal erosional reflectors inside the sandwaves and the truncation of the present-day profiles may reflect the effects of storms. The asymmetry of the tide in the area studied, shown by long-term current measurements, indicates that these sandwaves belong to classes III or IV of Allen's (1980a) classification; the observed structures correspond very well to the prediction of Allen's conceptual model, but we suggest that long term phenomena like equinox cyclicity, associated with storms, may be responsible for their origin rather than the neap-spring-neap tidal cycles responsible for the internal structure of intertidal bedforms.