Construction of a Soil Chronosequence Using the Thickness of Pedogenic Carbonate Coatings

A soil chronosequence is a quantitative description of how the properties of soils in a given area change with time. Chronosequences are important for several reasons, including their use as a tool for dating Quaternary landforms such as stream terraces, and should be included in earth-science education. An excellent index of soil age is the thickness of pedogenic calcium-carbonate coatings on the bottoms of pebbles in gravelly soils. Coating thickness is a simple and quantitative soil property and thus is particularly useful for educational purposes. We develop the general subject by constructing a soil chronosequence for the Lost River Valley of Idaho using this index. Reproducibility analysis indicates that the mean of thickness measurements of coatings from the carbonate soil horizon should be accurate to within 10 or 20%. The coatings have thickened through the Holocene and latest Pleistocene, but short-term-thickening rates have varied between 1.1 and ≈0.4 mm/10 ky. Long term rates are 6 ± 1 ×10−5 mm/y.