Geomorfología tectónica y evolución del relieve en un sector del piedemonte occidental de la sierra Chica de Zonda, Precordillera Oriental, Argentina

Abstract

In the western flank of the northern sector of sierra Chica de Zonda, Eastern Precordillera, San Juan province, Argentina, a geomorphological study was conducted to reconstruct the relief evolution during Quaternary time. Morphometric and morphodynamic information of drainage areas and accumulation piedmont areas was analyzed, and the causes for the formation of sieve lobes in the presently active channels of the alluvial fans were also investigated. The geomorphological study, based on photo interpretation, analysis of Google Earth satellite images, and field work, allowed to recognize various geomorphologic units like slope fans, alluvial fans, sieve lobes, terraces, among others, developed from 960 m to 750 m a.s.l. Two models of alluvial fan deposits were identified; the most ancient corresponds to segmented or telescopic alluvial fans, and the most recent to sieve lobes in active channels that discharge their sediment load over ancient alluvial fans, resulting in superimposed fan deposits. Besides, the fan area does not change with time, but the fan volume constantly increases, whereas the drainage basin area grows where erosion and active processes of capture take place. In this arid and tectonically active piedmont, the change of fan models may be associated to the combined effect of climatic oscillations and the regional compressive tectonics associated to the Villicum-Zonda reverse fault system. Some characteristics and processes contribute to sieve lobes formation, such as the stratification of limestones with carbonatic breccias, folded and homoclinal reliefs that facilitate dissolution, hollows, block fall, and detrital production, the existence of dip streams and strike streams, and finally the stream currents controlled by the homoclinal structure.