Quaternary development of migrating sediment waves in the Var deep-sea fan: distribution, growth pattern, and implication for levee evolution

A field of sediment waves built by turbidity currents on the Var deep-sea f an has been studied using a large amount of seismic-reflection data and cor es. To understand the spatial organisation and evolution of the sediment wa ves, maps of both surficial and an older subsurface wave field were prepare d. Three different sediment wave geometries (symmetrical to asymmetrical cr oss-section) were recognised and can be linked to particular styles of evol ution through time (from simple vertical aggradation to upslope and upcurre nt progradation). Each geometry appears to be linked with: (i) a particular location on the Var Sedimentary Ridge; (ii) the type of turbidite deposits ; (iii) the local gradient slope; and (iv) the height of the Ridge. Several factors control the nature and distribution of sediment waves and these fa ctors do not change significantly through time, as suggested by the common geometries, evolution and distribution of the sediment waves between the pr esent and fossil fields. Supercritical flow conditions and high sediment su pply allow the development of well-developed and prograding sediment waves, while subcritical flow conditions and low sediment supply allow the format ion of smaller and aggrading sediment waves. The impact of these two factor s is also influenced by the morphology of the fan valley, the height of the Ridge, and the type of transported sediment. The evolution of sediment wav e amplitude is also strongly influenced by the distance of sediment waves f rom the Ridge crest, while wavelength evolution is more influenced by slope gradient. The building of the Var Sedimentary Ridge and particularly the a symmetry and the overall morphology of the levee are directly controlled by the growth pattern of the sediment waves. (C) 2000 Elsevier Science B.V. A ll rights reserved.