Sedimentological analysis of sandy - gravel accumulations, Serra da Estrela plateaux (Portugal)

Sandy-gravel accumulations are frequent features on the plateaux of the Serra da Estrela II and other granitic mountains in Portugal. Their genesis has been attributed to both eolian and water processes and a detailed sedimentological study is needed to better understand the mechanisms involved. The present paper provides results obtained from the heavy mineral analysis and optical and scanning electron microscope study of samples from two sandy-gravel accumulations from the Serra da Estrela. The results indicate that the finer fractions of the original sediment have been illuviated. A well-sorted surface layer and poorly sorted subsurface of the accumulation have resulted from this process. A very short duration of eolian processes is evident from the analysis. Although wind seems to have been the responsible for the morphology of the accumulation, its action was not enough to produce significant abrasion in the surface of quartz grains