Formation of the Aude, Orb and Herault prodeltas and their characterisation using physicochemical and sedimentological parameters

The formation of Mediterranean prodeltas depends on microtidal estuarine dynamics. The study of the Aude estuary and others shows the usual presence of a salt wedge which induces the formation of two turbidity maxima created by two different processes [Pauc, H. 1997. Fluvio–marine interface in a microtidal mediterranean estuarine environment. The nepheloïd layer supply problem. Journ. Rech. Océanogr. 22 (3), 83–90]. The first process is a loss of charge due to the annulment of the current momentum, driving sedimentation of the silt-size material. The second process is flocculation, which results in deposition of fine sediment. The end results of the combination of these two processes is a sedimentary sequence with two distinct sediment units: silt below and clay minerals above. ometrical and mineralogical analysis of the sediment body enables the zone of sedimentation of each type of material to be determined, and hence the style of sedimentation to be inferred. Illite, quartz and dolomite are of detrital origin and accumulate close to the river mouths; while smectite is deposited by both dynamical and flocculation processes, and accumulating over the surface of the prodelta and also seaward by some 30–40 m depth. Calcite is of biogenic origin, and is found further offshore, associated with muddy sediments only.