Genesis and evolution of 'pseudocarniole': Preliminary observations from the Susa Valley (Western Alps)

In the Alpine geological literature some particular carbonate rocks having a vuggy appearance, associated with evaporite rocks, have a controversial origin and diversified, uneven, nomenclature. In this paper they are provisionally called 'pseudocarniole'. An excellent exposure along the Susa Valley (Italian Western Alps) permitted a relatively full analysis of a group of such vuggy rocks in situ. Five main lithologies have been identified with respect to their nature, shape, dimensions and organization of the clasts, also according to the matrix and the composition of the cements. Utilizing the interpretation of geological and geomorphological field data that cover these deposits, detailed stratigraphical descriptions and laboratory microanalyses (optical microscope and cathode-luminescence), a genetic interpretative model is proposed. The main formational process is dissolution, starting from solution of gypsum and anhydrite; then the processes affecting carbonate 'parental residual rocks' are considered. Thereafter a general instability of the rock masses is introduced with a consequent gravitational collapse. Other general processes are usually associated: tectonics, gravity and Plio-Quaternary karst phenomena. Finally, a particularly young age for the formation of the pseudocarniole deposits is noted, based on palynological data, Plio-Quaternary. © The Geological Society of London 2007.