In the Guadalquivir Depression, the foreland basin of the Betic Cordillera, there are large masses of Triassic lutites with evaporites that were emplaced, as an olistostrome, in the old Miocene sea. These materials, which from the hydrogeological point of view behave as an aquitard, contain brine groundwaters that upwell in numerous springs and seepages, usually of very low discharge. These waters have traditionally been used for the production of salt in small artisanal salt pans.
Measurements carried out in situ and chemical analysis of waters show that total dissolved solids values in water are between 100 and 300 g/L. The predominant ions are Cl- (up to 182 g/L) and Na+ (up to 116 g/L) and significant contents of SO42- (up to 11 g/L) and Ca2+ (up to 1.9 g/L) are also observed. These values are, respectively, close to saturation in halite and gypsum. Contents in Mg2+ (up to 1.3 g/L) and K+ (up to 0.9 g/L) are considerably lower and close to or lower than those of seawater.
The observed hydrochemical variability can be related to different mixing percentages of an ancient brine, possibly originated from marine waters, and meteoric waters of recent infiltration. Seawaters could come from the Miocene basin in which the olistostroma was emplaced and they would have dissolved gypsum and halite from the Triassic evaporites until saturation. After the emersion of the basin, the progressive erosive dismantling of the lutites with evaporitres and the limited infiltration of meteoric waters would favor the release of the brine and its mixture with less saline waters.