Estudio geoquímico de los yesos miocenos de la zona este de la cuenca de Madrid

Abstract

Some different types of gypsum deposits may be recognized within the Evaporite Facies of the Madrid Basin (Brea de Tajo-Drieves-Almoguera region). Trace elements analysis of these gypsum deposits allow to conclude that fractionation processes took place during their diagenetic evolution. From the set of trace elements that were analyzed, strontium and magnesium are the best to discriminate among diagenetic stages of formation of the evaporite facies, taking in mind these elements show distribution coefficients lesser than the unit (D<1). Thus, the different types of primary gypsum that we have observed possess Sr and Mg mean values of about 3270 p.p.m. and 1100 p.p.m., respectively, whereas secondary gypsum deposits display Sr mean values of 760 p.p.m. and Mg mean values of 410 p.p.m. The remainder elements do not show a so clear tendency, owing to either distribution coefficients near to the unit (K, Li, Fe, Na) or to extremely low contents (Mn, Ba).
From the results of the present study, geochemical behavior of some trace elements, mainly strontium and magnesium, must be considered a good criterion to indicate the diagenetic stage of formation of the gypsum deposits. Probably, ít may be applied to other comparative studies in definite geological settings.