Dolomite of Sciliar and Buchenstein Group.
About 234 million years ago, at the end of the Anisian stage, in the area
of Mount Cernera, to the south of the Ampezzo basin, there was an atoll
surrounded by a sea that became increasingly deeper in the direction of Cortina.
Various types of fossils have been found in these rocks that point to
different environments: the ammonites, animals that lived in the deep sea
around the atoll and the organisms that created the atoll itself
(algae, brachiopods, large and small bivalves, gastropods and sea anemones).
The discovery of ammonites is of great scientific interest: because these are animals that evolve in different and unique forms, it has in fact been possible to precisely reconstruct a geological time scale for that period.
So far as the organisms that created the atoll are concerned, their presence and subsequent disappearance would seem to point to the atoll, after an initial growth stage, having slowly and gradually sunk.