Carbonate aquifers in foreland tectonic settings can host important thermal springs although located in areas commonly not characterized by regional high heat flow values. In these cases, when thermal springs are located close or along the coastlines the subaerial and/or submarine thermal springs constitute the outflow of marine groundwater, flowing through localized fractures and karsitic rock-volumes. This is the case of springs occurring along the south-easternmost portion of the Apulia region (Southern Italy) where few sulphurous and warm waters (22–33 °C) outflow in partially submerged caves located along the shoreline, thus supplying the historical spas of Santa Cesarea Terme. Here, with the aim to define the origin of the thermal fluids and their deep path, we carried out the geo-structural survey of the area and detailed hydrogeological and geochemical analyses of the thermal spring fluids. In particular, the isotopes δ18O, δD, 13C in DIC, 34Ssulphate, 34Ssulphide, 3He/4He ratio and 13C in CO2 were used to define the origin of the thermal water and the recharge mechanism of the geothermal system while the isotopes 3H and 14C were determined for estimating the age of the thermal waters, resulting in older than roughly twenty thousands years BP. The results indicate that the thermal springs are fed by marine water, having reached Santa Cesarea Terme through a localized fracture network. This affects the evaporitic and carbonatic rocks that characterize the substratum of the Adriatic Sea in the offshore.
The present activity has been performed in the frame of the VIGOR Project, aimed at assessing the geothermal potential and exploring geothermal resources of four regions in southern Italy. VIGOR is part of the activities of the Interregional Programme “Renewable Energies and Energy Savings FESR 2007–2013–Axes I Activity line 1.4 ‘Experimental Actions in Geothermal Energy’. The authors acknowledge the management of VIGOR Project, and in particular: Dr. Piezzo of MiSE-DGENRE (Directorate General for Nuclear Energy, Renewable Energy and Energy Efficiency of the Ministry for Economic Development); Dr. Brugnoli, Director of CNR-DTA (National Research Council of Italy, Department of Sciences of the Earth System and Environmental Technologies); the coordinator, Drs. Manzella from CNR-IGG. Thanks are also due to the whole staff of the Santa Cesarea Terme spa for the availability displayed during the research activities performed for the pilot site of the study.
We are deeply indebted with Ingrid Stober, an anonymous referee and with the Editor, David Bruhn: their comments and suggestions helped us to largely improve the original manuscript.
- Carbonate reservoir
- Thermal springs