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Genesis of Hyperarid Soils of the Atacama Desert, Chile

Michael Howell
University of Nevada Las Vegas
Department of Geoscience Las Vegas, NV [email protected]

Soils in the Atacama Desert, Chile are dominated by salt mineral assemblages that are found nowhere else on Earth. These salts are derived from atmospheric, eolian, and groundwater origins. However, little is known about the pedogenic processes that control their distribution within Atacama soil. Three sites northeast of Antofagosta, Chile were visited and sampled to better understand the evolution of these rare and exotic salic-petrosalic soils. Preliminary X-ray Diffraction and Scanning Electron Microscopy results indicate that calcium-sulfates such as gypsum, bassanite, and anhydrite are restricted to upper unconsolidated horizons unless vertical fissures provide a conduit into indurated horizons. Indurated horizons are composed of primarily halite and nitratine. However, glauberite is found in trace amounts in both unconsolidated and indurated horizons. Two of the study sites contain an almost pure unconsolidated thenardite horizon and have patterned ground visible at the surface. The third site is lacking both the thenardite horizon and a well-developed patterned ground. I propose that the presence of soluble salts directly influences the observed surface features (polygonal patterns and desert pavement) and subsurface features (vertical fissures, horizonation, cementation). Ultimately, this data will be utilized along with the results of ongoing analyses to construct a theoretical pedogenesis model for hyperarid soils. Some key implications of this study include determination or reinterpretation of past climate and/or depositional environments preserved in paleosols / rock record, and the potential for water or hydrocarbon movement / containment / acquisition / recovery / remediation in these and other hyperarid soils.


AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid