Organización espacial de los sedimentos en conos aluviales del Pirineo Central Español

Abstract

The alluvial fans of the Ribera de Biescas, Upper Gállego Valley, Central Spanish Pyrenees, have been studied in order to identify the spatial organization of the sediment and to assess the most important features of their development. In the three alluvial fans studied the proximal area is dominated by debris flows, which are downwards substituted by transitional and fluvial deposits. The relative importance of each type of sedimentary facies is closely related with the size and gradient of the alluvial fan, as well as with the gradient in the final stretch of the ravine. In general, the size of the sediment decreases from the proximal to the distal area, while the roundness increases. Nevertheless, there are noticeable irregularities in the trend both in longitudinal and in transversal sense mainly due to the effect of debris flows advancing towards the inner part of each alluvial fan during the most intense peak-flows.