FROM Dr. Cesare Rizzetto – http://www.archeosub.it/articoli/geotec/caranto.htm

Every time a project of any kind appears on the city horizon that will affect the lagoon area, concern immediately spreads over the fate of the "caranto", almost as if the survival of the city and its lagoon were exclusively linked to this subsoil level, which is, overall, still quite unknown.

Far be it from me to lecture, my desire is to summarise for the reader what official science has elaborated over the last decades regarding the nature, origin, age and depositional environment of the "caranto".

I think it is useful to remember how, particularly the lagoon environment, is characterised by continuous change whose speed, relatively notable in geological terms, varies according to many parameters.

The lagoon we know is about 6000 years old; before, up to 11000 years ago, it was much smaller because the sea water level was considerably lower than today and vast areas now submerged, were, instead, emerged. The soils of the emerged areas, mainly made up of sandy clays and silty clays, were exposed for long periods to the action of an arid and freezing climate that determined their overconsolidation consisting in the drying and hardening of the constituents themselves: so that the "caranto", as this lithological level is called locally, appears as a silty or sandy clay, very compact, light grey in colour on which ochre streaks stand out.

Often, calcareous nodules are included in its mass: they are the result of the leaching process determined by rainwater on the carbonates present in the materials constituting the superficial part of this paleosol.

In the time interval between 11,000 and 6,000 years ago the climate progressively softened (end of the Wurmian glaciation), the average temperature progressively increased as did the sea level, so that the lagoon advanced until it reached its current boundaries.

The "caranto" disappears under the sediments that are deposited in an environment that has become lagoonal and that constitute the current muddy seabed.

Like its genesis, the morphology of the "caranto" is also strictly linked to the long period of emergence; in fact, since it is a paleosoil that slopes gently towards the coast, it has been subjected to the action of exogenous agents for millennia, first of all the erosion of surface waters that have dug more or less deep furrows in the material, sometimes removing it completely to redeposit it in different sites.

The theory of the spatial continuity of the "caranto", forming almost a plastron of fairly homogeneous thickness, is not sustainable. It must be disproved not only for the aforementioned erosive action but also for the fact that the overconsolidation was exercised only on the silty or sandy clays, and it is not certain that this composition is uniform over the entire depositional area.

If we then take into account that, starting from the lagoon boundary, proceeding towards the Lido, the absolute depth at which the "caranto" is found goes from approximately -2.0 m to approximately -7.0 m and that the depth of many lagoon canals (Vittorio Emanuele, Malamocco - Marghera, Giudecca - Porto di Lido, etc.) is maintained at levels above 10.0 m, we have further confirmation of the unsustainability of this theory.

That said, it is necessary to clear the field of another widespread belief, namely that the palisades on which many ancient Venetian buildings rest are supported by the "caranto".

It is pure coincidence that this level was reached by the piles which, I recall, are made of wood, have a diameter at the head of about 20 cm, a length of about 3.0 m and were driven in with a manual pile driver.

Their function was not to transfer the load of the buildings onto the load-bearing level of the "caranto", but rather to thicken the mud that overlies the "caranto", improving their mechanical characteristics and thereby increasing their load-bearing capacity.

It can be said that this is the great geotechnical intuition of the ancient Venetian builders.

The "caranto", therefore, must be considered as any level of the subsoil that reacts, in relation to its physical-mechanical characteristics, to the interactions that occur with the built environment, whether it is above or inside the level itself.