Relict Soils: The Other Kind of Paleosol
At the arid/hyperarid boundary in Chile, biota are essentially absent, chemical weathering nearly ceases, and soil formation is dominated by the retention of atmospheric solutes and dust. Relict Miocene soils now at this boundary commonly display complex geochemical signals - early stage weathering and mass losses coupled with later gains of atmospheric solutes - patterns consistent with predictions from independent climate proxies. In the semi-arid Wind River basin of Wyoming, gravelly soils on Pleistocene surfaces accumulated dense, laminated pedogenic carbonate clast-coatings that, if dated by U-series and analyzed by SIMS, provide long (<105 yr) oxygen isotopic time-series for soil pore waters that reflect past changes in moisture sources, evaporation, and atmospheric temperature.
Interpreting the geochemical signature of relict soils in hyperarid regions on Earth has direct relevance to Mars, which is mantled by soils that contain, in certain locations, an apparently chemically depleted silicate matrix overlain with soluble salts. In summary, ancient soils on terrestrial planetary surfaces are rich, albeit complex, archives of past climate change that are beginning to be deciphered by numerous researchers.