Nuevas aportaciones al estudio del «siderolítico» (Fm. Areniscas de Salamanca). Borde Oeste de la cuenca del Duero (Zamora)

Abstract

The Areniscas de Salamanca Formation, located in the western border of the Duero basin, has been studied by means of the polarized light microscope and the SEM. The study has brought out some interesting remarks: 1) important processes of redistribution of matter within the sediments displaying many bioturbation features (collapses, tubules, cutans, etc) all of them being previous to lithification; 2) presence of spicules of sponges (megascleras) appearing in the intermediate member of this Formation; 3) progressive enrichment in silica upwards with an increase in the contrasts of hues of the sediment due to Fe oxyhydroxides segregations. Although the dominant forms of silica are lepispheres, cavities filled up by idiomorphic crystals of tridimite, fibrous forms, microquartzs and isotropic opal are frequents. The presence of sponge spicules, both isolated or grouped, open the possibility (¿?) that this Formation had been related in some way to a seashore sedimentary environment in someone period of its geological history