Episodic eolian deposition in the past ca. 50,000years in the Alto Ilo dune field, southern Peru

摘要

The Alto Ilo dune field in the coastal desert of southern Peru is located at the edge of the Atacama Desert and is one of the driest landscapes on Earth. A stratigraphic sequence of eolian sands, paleosols and debris flow deposits are identified in this dune field spanning the past 55. ka. We infer that eolian deposition is preceded by an increase in sediment supply from local alluvial fans that are upwind of the Alto Ilo dune field and thus, reflects periods of relative hydrologic excess. Eolian sediment supply may increase also with the concomitant fall in sea level providing an additional foreland source area for eolian particles. The presence of paleosols indicate millennial-scale periods of locally wetter conditions, possibly associated with spread of "lomas" vegetation fed from coastal fog sources. Debris flows reflect significant rainfall events possibly associated with ENSO variability. The chronology is provided by optically stimulated luminescence using multiple aliquot regeneration protocols, which reveal four major eolian depositional episodes at ca. 55 to 45. ka, 38 to 27. ka, 22 to 16. ka, and 12. ka. Eolian deposition in the late Pleistocene dominates the record and is generally coincident with metrics of hydrologic excess from the Peruvian Andes and the Altiplano, which appears to translate into enhanced sediment availability on the coast. A significant period of soil development between 18 and 13. ka is consistent with timing of Central Andean Pluvial Event and indicates widespread wet conditions. The Holocene record of eolian deposition is sparse reflecting limited alluvial fan sources and decreasing particle availability upwind with the rise in postglacial sea level.