Published online by Cambridge University Press: 09 July 2018
Fine-grained sediments are a major parent material in Ebro Valley soils. During the 1960s, the area was transformed by irrigation and soils underwent serious degradation processes. The sediments have a fine texture, high CaCO3 contents and high salinity-sodicity levels, and contain illite as the most important phyllosilicate in the fine fractions. Two groups of finely laminated organization have been recognized in terms of layer thickness and grain-size distribution. Based on texture, the microstructure of the silty and clayey layers is different, irrespective of their mode of formation; porosity characteristics also differ between layers, leading exclusively to a capillary evaporation flow that results in salinization of the plough horizons. The sediments are formed by two different mechanisms, each layer resulting from uninterrupted sedimentation of a suspension or from deposition of suspended particles by water discharge.