Caracterización geoquímica de la ruptura sedimentaria entre los yesos de la unidad salina e intermedia de la cuenca de Madrid

Abstract

Two sedimentary Unities of gypsum deposits are defined in the Tertiary of the Madrid Basin, Spain. 80th Unities are formed by gypsum materials with different features although the separation between the lower and the upper Unities can be very difficult in some outcrops. It is due to strong processes of gypsification which transform the primary textures in a secondary texture formed by macrocrystalline mosaics of gypsum. The objective of this work is related to the aplication of trace element geochemistry to discriminate between lower and upper Unities. So, Sr, Mg, and Fe can be a useful elements to separate lower Unity from Upper one. A factor analysis was also carried out with the geochemical results. The values of the factors obtained let us to define the position of the sedimentary rupture between the two Unities. This position is c1early differentiated by a simultaneous change in both factors from negative to positive values. The results obtained show that terrigenous gypsum (Upper Unily) are formed by erosion of anhidrites from Lower Unity. These anhidrites, previously, have been transformed to gypsum in a environment of high salinity.