Thermo-mineral waters from the Cerna Valley Basin (Romania)

Abstract

In the south-west of the Southern Carpathians, upstream from the confluence of Cerna with Belareca, an aquifer complex has developed, strongly influenced by hydrogeothermal phenomena, acting within two major geological structures, the Cerna Syncline and the Cerna Graben. The complex consists mainly in Jurassic and Cretaceous carbonate rocks, as well as in the upper part of the Cerna Granite, highly fractured, tectonically sunken into the graben. As a result of the tectonic processes which occurred after the end of the Jurassic-Cretaceous sedimentation cycle, limestones may be encountered at 1100 m altitude in the Mehedinţi Mountains, at 150 ¬¬600 m in the Cerna Syncline or sunken into the Cerna Graben down to depths of 1075 m. In certain sections along Cerna, graben limestones outcrop in an intricate relationship with those of the slopes, facilitating the existence of very large scale uni- or bidirectional hydrodynamic links. The geothermal investigations have shown the existence of some areas with values of the geothermal gradient falling into the 110-200°C/km interval, and temperatures of 13.8-16°C at the depth of 30 m (VELICIU, 1978). The zone with the maximal flux intensity is situated between the Băile Herculane railway station and the Crucea Ghizelei Well, an area where 24 sources (10 wells and 14 springs) are known. The geothermal anomaly is also extended to the south (Topleţ), north (Mehadia) and north-east (Piatra Puşcată), a fact which is stressed by the existence of hypothermal springs with low mineralization. The physical-chemical parameters of the sources show a strong, north-south, variability. At the entire thermo-mineral reservoir scale, the temperature of the water sources, the total mineralization and the H2S quantity are increasing from the north to the south, and the pH and natural radioactivity are diminishing with the same trend.