The formation of caliche in soils of the Mojave Desert,California |
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| Authors: | William H Schlesinger |
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| Institution: | Department of Botany, Duke University, Durham, N.C. 27706 USA |
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| Abstract: | Radiocarbon and 230Th-234U dates of calcic horizons from calciorthid soil profiles in the Mojave Desert were used to calculate the rate of deposition of pedogenic CaCO3. A major period of CaCO3 deposition appears to have occurred about 20000 yBP forming calcic horizons below 100-cm depth during a climatic regime with greater effective rainfall than in the present. The overall rate of deposition has been 1.0 to 3.5 g CaCO3/m2/yr during soil formation. This rate is consistent with present-day rates, assuming that the atmospheric deposition of Ca limits the process. Stable isotope ratios in calcic horizons indicate that CaCO3 precipitated from a soil environment with CO2 of ? 15.5%. (vs. PDB) and H2O of + 2.0%. (vs. SMOW). These values suggest that CaCO3 precipitates when seasonal drought simultaneously lowers soil pore pCO2 and enriches soil water 18O by evaporation. The role of soil calcic horizons in the global geochemical cycle of carbon is discussed. |
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