Results of late-wurmian to present-day climatic-geological evolution on to spatial variability of pedologic-geological characters of the AOC Gaillac terroirs (Tarn, Midi-Pyrénées)

The AOC Gaillac area is divided into three main terroirs : « The left bank terraces », « The right bank coteaux » and « The plateau Cordais ». This division is valid at a regional scale, but it suffers of a number of local-scale exceptions. This spatial variability of the pedologic-geologic characteristics at the plot scale has been derived mainly from the main late-Würmian solifluxion phase occurring at the transition between the peri-glacial climate and the Holocene temperate conditions (13,000-10,000 yrs BP). This soil movement processing has generated tongue-shaped features composed of a mixed molassic-fluviatil material mostly on north-oriented slopes, concealing the in-situ molassic bedrock. This spatial variability has to be taken into account in any viticultural zoning strategy using extraction of morphometric data from a Digital Elevation Model (DEM) as slope gradient and slope orientation maps.