Papel de la porosidad en el proceso de silicificación del borde occidental de la cuenca terciaria del Duero. Nuevas aportaciones e implicaciones morfológicas

Abstract

Silicified sedimentary deposits covering the hercynian basement in the western border of the Duero Tertiary Basin (Zamora province) are studied by means of micromorphological, mineralogical and geochemical criteria. Three profiles were investigated. One of them (arroyo Perdigón profile) was selected as the most representative and complete. Chemical analysis, optical microscopy, XRD, SEM and EXRDA microprobe were the used techniques. The samples studied shown that, previously to sedimentation, the materials had a residual and inherited mineralogy from previous weathering processes. During sedimentation, they underwent important bioturbations under more or less hydromorphic conditions leading to the re-arrangement of matter and oxy-hydroxide segregations. At the end of sedimentation, a silicification process affecting both, sediments and weathered basement, took place. It represents a new weathering process leading to dissolution of clays, new residual minerals and CT opal concentration. This last process is related to an old surface whose remnants appear uneven by the alpine tectonic phases affecting to this region during the Tertiary.