Sedimentología e hidrogeoquímica de las Lagunas de El Cristo y de La Cervera(Salamanca)

Abstract

The El Cristo and La Cervera ponds lie on the Neogene clastic deposits of the Ciudad Rodrigo basin. Their origin matches a hydroeolic model and the ponds were probably developed during the recent Quaternary. The neotectonic framework, the substrate lithology, the flat geomorphology and the semiarid regime with winds along the NE-SW trend favoured their genesis. The composition of water is of HCO3 --Cl--Ca2+ type, with 124 to 164 mg/L for TDS (total dissolved solids), and an average pH 9.61 for the El Cristo pond and 7.6 for the La Cervera pond. The high values of d34S in the dissolved sulphate suggest the importance of the bacterial sulphate reduction in the pond floor. The low d13CDIC values indicate the predominance of respiration processes and organic matter oxidation related to plants with C3 metabolism. The XRD data of whole rock from the pond sediments indicate that quartz is the main component with lesser proportion of K-feldspar and clays. The sediment fraction < 2 ìm is mainly represented by kaolinite, some illite and, in the exposed marginal sediments, smectite. The hydrological features, the geological framework, the water composition, and the mineralogy of the pond deposits indicate an open lacustrine system where the recharge and discharge were mainly underground.