Late Quaternary morphodynamics in the Quebrada de Purmamarca, NW Argentina

This study aims to document the geomorphic, sedimentary and paleopedogenic archives in the Quebrada de Purmamarca. The paleoenvironmental interpretation of these archives and the reconstruction of landscape evolution are mainly based on field observations and geomorphological mapping (May 2008). A series of aggradational terraces mostly consisting of coarse debris-flow deposits are the main focus of this investigation. While the associated cut-and-fill processes are probably the result of an interplay between climatic and tectonic controls, the deposition of the youngest terrace level (> 150 m thickness) may likely be attributed to a drop of the periglacial belt of more than 1000 meters below its modern elevation. For the time after terrace accumulation has ceased, the interpretation of alluvial fans, aeolian sand and a well-developed paleosol points to Late Quaternary humidity changes as an important control on landscape evolution. The major phase of downcutting and incision significantly postdates the end of terrace deposition and may have been triggered by markedly increased amounts of monsoonal precipitation. Finally, minor humidity changes of possible Holocene age are indicated by paleopedogenic and geomorphic observations on terrace surfaces and along valley slopes.