Pleistocene-Holocene geomorphologic interactions between mountain catchment and foreland in the Argentinean Andes, 33°S.

PEPIN, E.; CARRETIER, S.; HERAIL, G.; CHARRIER, R.; FARIAS, M.; REGARD, V.; GARCIA, V.; GIAMBIAGI, L.

Londres, Reino Unido

Simposio; William Smith Meeting 2010 - Landscapes Into Rock.; 2010

Geological Society of London

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --> Interactions between erosional and depositional landscapes are an interesting issue in Geomorphology. For instance the relationships between an erosional mountainous catchment providing sediment and the alluvial fan which control the mountain base level are still not well known. These sub-systems are interdependent and are continuously changing because of climate, tectonics or boundary conditions variations. Thus, understanding the geomorphic signature of climate or tectonic changes in a mountain requires studying the whole catchment-fan system. The catchment-fan system of las Tunas, Argentina is located southern of Mendoza city, between latitude 33°S and 34°S a tectonically active area where the deformation is propagating into the foreland. This natural example illustrates how strong catchment and foreland sedimentation dynamics are linked. Indeed the alluvial fan of las Tunas has been strongly entrenched and three main levels of terraces are clearly visible. These terraces are connected to fill and strath terrace along the main stream of the mountain catchment and until more than 10 km upstream the fan apex. The goal of this study is two folds: 1- to determine the origin of entrenchment and sedimentation cycle in the whole catchment-fan system, 2- to propose, an evolutional model in order to explain the current landscape. GPS topographical profiles of each terrace have been measured in the foreland section. A detailed study of the topography has been made using SRTM and GDEM data. Three depth versus 10Be concentration profiles allow the abandonment age of the three main terraces to be determined. In addition, six 10Be additional surface samples and Ar/Ar dating of two ash samples give additional ages of depositions. These data indicate that sedimentation and entrenchment in the mountain and in the foreland are intimately linked and evolve synchronously. The last main entrenchment occurred at 19ka, just after the last glacial maximum. Finally, this study suggests that despite its active tectonic context, the catchment-fan sedimentary dynamics (entrenchment and sediment deposition) is mainly controlled by quaternary climate variations, consistently with another study in Tien Shan, and numerical model results.