Università “Roma Tre”, Dipartimento di Scienze, Largo San Leonardo Murialdo 1, 00146 Roma
Speleothems (stalactites and stalagmites) in natural and artificial caves can be used as historical archives to reconstruct palaeoclimatic and palaeoenvironmental conditions in the past. This can be obtained through chemical investigation of the oxygen and carbon contained in the carbonate deposits, whose growth is related to the CO2 dissolved in the dripping water. This gas can originate from the organic activity in the soil or, in areas affected by volcanic or hydrothermal activity, can be of deep provenance. Specific investigation on chemical and physical properties of speleothems, coupled to Uranium-series dating, allow to distinguish between the two origins. In case of CO2 derived from the soil, the chemical record can give paleoclimatic and paleoenvironmental information (on temperature and precipitation), whereas deep origin CO2 may be employed to reconstruct the seismic and volcanic evolution of a given area.
The described activities developed from a pilot study focused on an old stone mine (Centroni cave) located in the south-eastern end of Roma, where abundant speleothems have been depositing since 2,000 years ago, with evident periodic hiatuses in the precipitation process. Cyclic interruptions in the speleothems growth, along with an increase in deep CO2 proportions, are correlated with the opening of fractures preceding earthquakes, historically documented in the city of Rome and surroundings.
Further studies have been carried out on the Ancient Roman age artificial outlet of Gabii Lake that occupied the crater of Castiglione, not far from Tivoli town. A first exploration of the outlet revealed the presence of speleothems. They appeared to have only few growth unconformities. The chemical records do not indicate significant changes or trends that can be interpreted in terms of variation in the proportion of deep CO2. The chemical signature can be explained more simply as due to small fluctuations related to the climatic and environmental conditions.