Traces of ancient glaciations in karst environment - a case study in the Venetian Prealps

To reconstruct the ancient glaciations of a mountainous area, it is necessary to consider together, in their topographic contexts, the forms of erosion and those of accumulation, aiming to model the relative glacial systems, which can be understood on the basis of the interrelationships between the various forms. In the karst areas, the forms of glacial erosion are often easily recognizable, given that the geomorphological dynamic favours their conservation. The very ancient deposition forms, on the other hand, are hardly detectable or absent given that chemical erosion contributes to the decrease in volume of the moraines until their total disappearance. As an exemplary case, the relict forms of the ancient local glacial system of Valon del Malera, developed in jurassic limestone and Main Dolomite (Dolomia Principale), partly preserved in the Lessini Mountains (Prealpi Venete, NE Italy) and partly in the nearby Carega massif (Piccole Dolomiti), are illustrated. The forms of erosion document the dismantling of a segment of a glacial valley due to accelerated erosion phenomena attributable to active tectonics along an important fault system. Other segments of the trough-shaped glacial valley are very well preserved. On the other hand, forms resulting from the “over-imprinting” of some ancient morainic ridges are detectable, due to the fact that in favourable cases the morainic cover has reduced the rate of lowering at the cover-rock interface of the underlying limestone, in comparison with the surrounding rocky surfaces not covered by till deposits, causing the formation of rocky ridges. However, the temporary aquifer hanging within the moraine has favoured the development of grike type covered Karren in the limestone, with isolated spikes or pillars of rock. Ridges mainly or totally formed by rock in place are described, which, according to all evidence, seem to be the result of the “over-imprinting” by ancient moraine ridges partly or totally eroded.