Publication Date:
2012-07-01
Description:
The Atacama Desert has experienced a long and protracted period of hyperaridity that has resulted in what may be the most unusual biome on Earth, but the duration of this aridity is poorly constrained. We reconstructed aspects of the fluvial and geochemical history of this region using integrated landscape features (alluvial fans, hillslope soils, soil chemistry, river profiles) in the southern portion of the present desert. Topographic reconstructions of a large watershed (11,000 km2) show deep incision and sediment removal between the late Miocene and the end of the Pliocene, and modest to negligible incision in post-Pliocene times. These changes in incision suggest an ∼50–280× reduction in river discharge, which should reflect corresponding changes in precipitation. Changes in the nature of hillslope soils in the Atacama Desert indicate that in the Pliocene or earlier, hillslopes were mantled with silicate-derived soil. This mantle was stripped off and locally deposited as alluvial fans (late Pliocene to early Pleistocene) that now block or otherwise cause a rearrangement of Pliocene and earlier river channels. Finally, the hillslopes have largely accreted a soil mantle of dust and salt since the apparent late Pliocene stripping, suggesting a decline in annual precipitation of at least 125 mm yr−1 or more (mean annual precipitation [MAP] is now
Print ISSN:
0016-7606
Electronic ISSN:
1943-2674
Topics:
Geosciences
