The soil-evolution model as a framework for evaluating pedoturbation in archaeological site formation

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Abstract
Soil and near-surface material affected by pedogenesis is the principal medium in which field archaeologists dig. Soil encases the cultural resources from which prehistoric human behavior is inferred. In fact, the various soil properties, factors, and conditions often determine the extent to which perishable materials are preserved, modified, moved, or destroyed by post-burial processes. The soil is not, however, the same material that was originally present when the artifacts were deposited. The dynamic nature of the soil system is such that changes in its morphology, thickness, and biophysicochemistry occur over time, and the sum of the changes is different from one site to another. Changes may include evolution of new properties, features, and horizons, such as illuvial cutans of clay, humus, iron and manganese, argillic horizons, and concretions, among others. Such endogenous or intrinsically evolved properties and features are termed "pedogenic accessions." Once formed, such accessions may persist, undergo further change, or be obliterated, as when clay cutans are broken up in Bt horizons via shrink-swell action, or when carbonate nodules dissolve following an increase in soil acidity. Further, some accessions may cause feedback processes that redirect pedogenic pathways in progressive or regressive directions. For example, certain subsoil horizons may gradually increase in density until threshold development is reached (fragipans, clay pans) after which they become barriers to downward water percolation and function as aquitards or aquicludes. Feedbacks such as perched water tables and attendant profile gleying, mottling, and cessation of profile deepening may be triggered. Then there are the