Geomorphologic evidence for the late Pliocene onset of hyperaridity in the Atacama Desert

Research Article| July 01, 2012 Geomorphologic evidence for the late Pliocene onset of hyperaridity in the Atacama Desert Ronald Amundson; Ronald Amundson † 1Department of Environmental Science, Policy and Management, University of California, 130 Mulford Hall, Berkeley, California 94720, USA †E-mail: earthy@berkeley.edu Search for other works by this author on: GSW Google Scholar William Dietrich; William Dietrich 2Department of Earth and Planetary Science, University of California, McCone Hall, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Dino Bellugi; Dino Bellugi 2Department of Earth and Planetary Science, University of California, McCone Hall, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Stephanie Ewing; Stephanie Ewing 3Department of Land Resources Kunihiko Nishiizumi 4Space Sciences Laboratory, University of California, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Guillermo Chong; Guillermo Chong 5Departamento de Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile Search for other works by this author on: GSW Google Scholar Justine Owen; Justine Owen 1Department of Environmental Science, Policy and Management, University of California, 130 Mulford Hall, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Robert Finkel; Robert Finkel 2Department of Earth and Planetary Science, University of California, McCone Hall, Berkeley, California 94720, USA6Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94550, USA Search for other works by this author on: GSW Google Scholar Arjun Heimsath; Arjun Heimsath 7School of Earth and Space Exploration, Arizona State University, 548 Physical Sciences F-wing, Tempe, Arizona 85287, USA Search for other works by this author on: GSW Google Scholar Brian Stewart; Brian Stewart 8Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA Search for other works by this author on: GSW Google Scholar Marc Caffee Marc Caffee 9Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Ronald Amundson † 1Department of Environmental Science, Policy and Management, University of California, 130 Mulford Hall, Berkeley, California 94720, USA William Dietrich 2Department of Earth and Planetary Science, University of California, McCone Hall, Berkeley, California 94720, USA Dino Bellugi 2Department of Earth and Planetary Science, University of California, McCone Hall, Berkeley, California 94720, USA Stephanie Ewing 3Department of Land Resources Geomorphologic evidence for the late Pliocene onset of hyperaridity in the Atacama Desert. GSA Bulletin 2012;; 124 (7-8): 1048–1070. doi: https://doi.org/10.1130/B30445.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract 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 <3 mm yr−1). Embedded in the long post-Pliocene era of salt accumulation, there are a variety of features suggesting overland flow on hillslopes (rills, striped gravel deposits, piping, and water spouts) and large, infrequent storms that infiltrated gentle alluvial fans (due to the depth of salt-rich horizons). Despite evidence for episodes that punctuate the hyperaridity, the magnitude and duration of these pluvial events have been insufficient to remove the regional accumulations of sulfate, chloride, and nitrate. The late Pliocene cessation of many fluvial features is coincident with recent research on the tropical Pacific, which shows that the Pacific was in a permanent El Niño state until ca. 2.2 Ma, at which time sea-surface temperatures offshore of South America declined greatly relative to those of the western Pacific, in turn setting up the present El Niño–Southern Oscillation (ENSO) climate system. These observations indicate that the latest period of aridity has been prolonged and largely continuous, and it appears to have occurred in step with the onset of the ENSO climate system, beginning ∼2 m.y. ago. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.