At the southern edge of the Lessini Mountains (Venetian Prealps, Italy), a well-developed palaeokarst network is found in the hills surrounding Verona, called Torricelle. Palaeokarst cavities are fossilized by palaeosols of mostly limonitic composition (“yellow ochres”), which were mined for centuries for pigments. In the current interpretation, the age of the palaeokarst features is set between the Oligocene and the early Miocene, when a regression took place in the central Lessini Mountains which partially emerged. In the Torricelle area, ochres are believed to be the insoluble residuals of subaerial weathering of upper-Priabonian marly limestones.
The exploration of paleokarst cavities and of the surrounding area has led to the discovery of terrigenous-calcarenitic layers embedded in the palaeosol fillings, containing foraminifera assemblages whose age ranges from the upper Eocene to the upper Oligocenelower Miocene. In particular, one of the caves is developed in the Marne di Priabona Formation (lower Priabonian), and its ochre filling contains fossiliferous layers with Priabonian Foraminifera assemblages. The presence of fossils whose age is comparable to that of the host rock is a testimony of upper-Eocene eogenetic karst. Furthermore, the presence of ochre fragments embedded in nearby Ypresian and Bartonian limestones provides evidence of emerged land and pedogenesis in early and middle Eocene, partly disproving the current interpretation of ochres’ formation.
These findings provide evidence that ochre formation, karst development and its fossilisation started earlier than Miocene, as previously thought. Phenomena began in early Eocene and ended in Miocene, over a time span of at least 30 million years.