Quaternary telescopic alluvial fans. Argentine Andean Ranges

摘要

The largest rivers that drain the Argentine Andean Ranges are characterised by incised valleys in highmountains and by a variety of Quaternary terraces. Their convex-up morphology suggests that these terracesare related to a series of alluvial fans developed where the tributaries join the main river. The succession ofalluvial aggradation and degradation is controlled by local base level variation conditioned by temporarylake development in the main river valley. All these factors give rise to the segmented morphology of thefan surface, yielding a telescopic relationship. The variation in the morphology and number of terracessuggests that they are not controlled by a general base level. Neither tectonic activity nor significant climaticchanges account for the alluvial fans at the confluence of the tributaries and the main river. Significantvariations in rainfall or thunderstorms induced by the El Niño Southern Oscillation (ENSO) could explainthe genesis of these telescopic alluvial fans