Descripción y estudio preliminar del origen de la Depresión de Valdespartera (Zaragoza)

Abstract

The central Ebro Basin was filled by evaporite (gypsum, principally) and carbonate deposits of a Neogene age. During the Quaternary age the fluvial activity caused the development of structural platforms and several nested levels of terraces and pediments. It is very frequent to find small depressions that, originally, had no connection with the drainage system. We study one of these, the Valdespartera depression, which is developed following the boundary between two different aterials, the gypsum Tertiary layers in the south and the terrace and pediment Quaternary deposits in the north. From the study of the morphological charactenstics, several factors which cooperate in its genesis can be pointed out: Structural factors (mainly he presence of fractures), the preferential erosion along the boundary between the Tertiary and Quaternary sediments, the dissolution of gypsum layers and piping processes. Wind could be an important transport agent of fine sediments, eventhough no proofs of its importance were found. The main process which generated this depression is gypsum dissolution as, the presence of alluvial dolines in the region, of small basins in the infilled valleys and a surface with an intermediate slope between the Tertiary and the bottom of the depression, indicate. Piping produces dragging of detrital materials in the conduits. These processes are favoured by fractures and the weakness of the contact between Tertiary and Quaternary materials.