CNR-IGG

Platanares and Azacualpa geothermal sites of Honduras are located in an inner part of the Caribbean Plate far from the active volcanic front of Central America. Here geology indicates that there are not the conditions for the occurrence of shallow magmatic heat sources for high-enthalpy geothermal resources. Geothermal perspectives are related to the possibility of a deep circulation of meteoric water along faults and the storage of the heated fluid in fractured permeable reservoirs. Geochemical geothermometers indicate a temperature for the deeper part of the geothermal reservoir close to 200 °C for Platanares and of 150–170 °C for Azacualpa. Calcite scaling, with subordinate silica deposition has to be expected in both sites. CO2 soil flux investigations have been carried out in both areas and reveal the presence of positive anomalies likely corresponding to the presence at depth of fractured degassing geothermal reservoirs. Compared with the geothermal areas of Central Italy whose reservoirs are hosted in carbonate rocks, e.g. Latera (Chiodini et al., 2007), the CO2 soil flux measured in Honduras is significantly lower (mean of 17 g/m2day at Platanares and of 163 g/m2day at Azacualpa) probably because of the dominant silicate nature of the deep reservoirs.

Along the Stura di Lanzo River, 20 km north of Turin, several large stumps in growth position crop out, thus providing a well-preserved example of fossil forest. This is formed by conifers which bear the Glyptostrobus europaeus type of cone-foliage and the Glyptostroboxylon rudolphii wood-type. Stratigraphic and plant taphonomic analyses of the outcropping succession clearly indicate that the palaeoenvironment was a densely-vegetated swamp, laying nearby one or more active fluvial/deltaic channels, in which coarse cross-bedded sands were deposited. The fossils are embedded in fine-grained continental sediments referred to the «Villafranchiano» unit, a term used in the Piedmont region (north-western Italy) to designate coastal to continental deposits which conformably overlay Pliocene marine successions. In this paper we present new data which better characterize the chronostratigraphy of the Stura di Lanzo Fossil Forest (FF) succession and similar deposits studied at the Front site. The integrated magnetobiostratigraphic approach, applied to both outcropping sections and subsurface deposits, permits to attribute the FF to the Kaena subchron. On the basis of these new magnetobiostratigraphic data, a strongly supported correlation between the FF and the Villafranchian “type-section” of Villafranca d’Asti is proposed. Furthermore, the well-constrained FF chronostratigraphy adds new data to the Middle Pliocene vegetation history, since an adequate palaeofloral documentation for the Kaena time interval was still lacking in Italy.