REDEFINING THE TARAPACA PEDIPLAIN; ANALYSIS OF RELICT SOILS IN THE NORTHERN ATACAMA DESERT, CHILE

The Atacama Desert in northern Chile preserves relict landscapes that are important for understanding the relationship between climate change and uplift of the Central Andes. The relict landscapes are also significant in understanding the antiquity of this hyper arid region. The northern Atacama Desert surface, the Tarapacá Pediplain, is capped by a well-developed gypsic soil in some locations, as expected for a surface thought to have been stable since ~10 Ma. However, field observations indicate that this well-developed gypsic soil is only present in some locations, and that it is actually a relict soil reflective of climatic and environmental conditions during the Middle and Late Miocene. In many localities the relict gypsic soil is buried by younger geomorphic surfaces and landforms. These data indicate that a wide variety of geomorphic activites are still active on the Tarapacá Pediplain, and that the actual Middle Miocene relict landscape encompasses a much smaller area than previously described. Field, geochemical, and microscopic (LM and SEM) analysis of buried, relict, and modern soils indicate a more detailed geomorphic and climatic story for this area. U-Pb dating of detrital zircon from the top of the underlaying El Diablo Formation, the relict soil, and covering sediment help to constrain the initiation and developoment of the Tarapacá Pediplain.