Mathematics – Logic
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p71a0443s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P71A-0443
Mathematics
Logic
1045 Low-Temperature Geochemistry, 3665 Mineral Occurrences And Deposits, 5415 Erosion And Weathering, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
The Atacama Desert of northern Chile is the driest desert in the world, having experienced its present hyper-arid climate since the Miocene. While Mars is vastly more dry and cold than the Atacama, the Atacama environment may be one of the best terrestrial Mars analog environments accessible to researchers. Because of the long-term hyperaridity, the soils retain atmospherically-derived elements, which accumulate to economically valuable quantities. The objective of this work was to examine physical and chemical evolution of the soils of the hyper-arid Atacama Desert to provide insight as to what soil properties may be found on Mars. Three soils were excavated and examined on widely representative landforms along a south to north transect (Copiapo > Altimira > Yungay) that coincides with decreasing moisture levels (~15mm to ~2 mm yr-1, south to north). Total chemical analyses were used to calculate strain (i.e. volume change) and elemental gains or losses (\tau). Relative to parent material values, the Yungay and Altimira soils have expanded over 400% in certain horizons, while the Copiapo soil has collapsed by as much as 48%. The expansions are driven by elemental gains; the collapse by weathering losses. Calculations of \tau indicate a 380 000% enrichment in Cl (halite) in the lower horizons, and S enrichments (anhydrite, gypsum) as high as 50 000% in the upper horizons, of the Yungay soil. The Altimira soil had a 110 000% enrichment of S (gypsum) and a 16,000% enrichment of carbonate, reflecting the higher precipitation and the relative solubility of salts. The southern, higher rainfall Copiapo soil had small \tau values for S (283%) and Cl (63%) in the middle horizons, but significant gains of CaCO3 (\tau values as high as 4 000% in certain horizons). In general, the type and depth of Cl, S, and CaCO3 enrichment in the soils varied predictably with rainfall. The results of this work, which document enormous atmospherically-derived elemental gains and volumetric expansion, differ from trends in soil evolution in humid conditions which show pervasive weathering losses and collapse. From the precipitation gradient, it appears there is a critical water balance for soil formation below which the long-term accumulation of atmospherically-derived elements (e.g., S, Cl) exceeds weathering losses and landscapes undergo continual expansion (e.g., Yungay soil) as opposed to collapse (e.g, Copiapo soil). This critical crossover point appears to be quite arid, possibly between 2 and 15 mm of annual precipitation. Elevated levels of S and Cl found at the Viking and Pathfinder sites are consistent with our expectations of soil formation during long periods of growing aridity and pervasive planetary aerosol transport. Finally, the Atacama Desert soils provide insights into the type and concentrations of near surface mineralogical resources available to any future manned mission.
Amundson Ron
Ewing Stephanie
McKay Chris
Rhodes K. W.
Sutter Brad
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