Preliminary hydrogeological characterization of an evaporite karst area (province of Cordoba, South Spain)

Abstract

The northern sector of the Subbetic Domain in the Betic Cordillera is formed by an olistostrome unit known as the Chaotic Subbetic Complex (CSC). This megabreccia is basically made of Triassic (Keuper) clays and evaporites (gypsum, anhidrite and halite) as well as blocks of other lithologies (limestones, dolostones, sandstones, etc). Despite that low permeability has been traditionally assumed for these materials, water flow and storage through them is likely derived of their aquitard behavior, but also because of the highly permeable conduits generated by dissolution/karstification processes within the evaporite rocks. The geological complexity of the CSC materials determines their hydrogeological heterogeneity, with groundwater flow systems of different length and various scales from recharge areas to discharge zones. Three springs draining the CSC outcrops have been identified around an evaporitic karst plateau located between the Anzur River (to the North) and the Genil River (to the South), in the province of Cordoba (Spain). Data logger devices have been installed in two of them, located at the Anzur River (left margin), providing an hourly record of discharge, electrical conductivity and water temperature. Water samples have been collected fortnightly for subsequent chemical analysis. After two years of record, the results obtained show that the response of the springs to rainfall events is completely different between them. One has a clearly karstic behavior, with a rapid response to recharge whereas the other one is more inertial, and variations in its waters occur in a yearly scale. This is an evidence of the aforementioned hydrogeological heterogeneity of the CSC.