Geomorphology of the piedmont of the Serranías Occidentales: Influence of a folding morphostructure in the Sierras Pampeanas Australes, San Luis, Argentina

Abstract

The geomorphology of the western piedmont of the Serranías Occidentales, within the southern Sierras Pampeanas, is presented. The hierarchical analysis of the relief allowed us to distinguish 4 Geomorphological Regions, 2 Geomorphological Associations and 11 Geomorphological Units. Within the Geomorphological Association of the Piedemonte Occidental de las Serranías Occidentales, we recognize erosional and aggradational geoforms. The latter are grouped into 4 main types: A) large sandy-muddy alluvial fans, B) sandy-muddy terminal fans, C) small gravelly-sandy alluvial fans, and D) piedmont with channelled flows. The characteristics of alluvial fans are closely related to their watersheds; the relationship between the fan area shows a positive trend for all cases; similarly, the textural characteristics of the deposits are directly related to the source zone. However, the sandy-muddy fans present sizes and slopes that differentiate them from the alluvial deposits defined for other Pampean piedmont of the southern sector; their dimensions greatly exceed the frequent sizes, while the slope values are lower. The deposits that make up the fans are linked to sedimentary sequences with Pleistocene to upper Holocene ages and the current wedging of its main channel is interpreted to be associated with a climate variation and changes in their local base levels, which could be linked to the decrease in the flow of the Desaguadero River and neotectonic activity.