Soil Stratigraphy

Soils have been employed in archaeological stratigraphy since at least the 1930s, including topical discussions of the significance of soils in stratified deposits (e.g., Leighton, 1936, 1937; Bryan and Albritton, 1943). This apparently was for several reasons. The unique physical and chemical properties that distinguish soils from sediments make soils quite useful for stratigraphic subdivision and correlation. In particular, pedologic features, most notably soil horizons, are often the most visually prominent features in stratified deposits. Furthermore, much of the early archaeological pedology was done by individuals trained in Quaternary geology (e.g., Leighton, 1937; Bryan, 1941a; Bryan and Albritton, 1943; Movius, 1944, pp. 49–62), in which soils have been recognized as stratigraphically important since the late 19th century (Bowen, 1978, pp. 10–56; Finkl, 1980; Tandarich, 1998a). The recognition of soils and the differentiation of soils from sediments in archaeological contexts is one of the most fundamentally significant aspects of geoarchaeological stratigraphy. This initial step in stratigraphic interpretation is crucial to most of the applications of pedology and soil geomorphology discussed in subsequent chapters. Because soils indicate periods of stability or hiatuses in deposition, the identification of soils or the lack thereof in a stratigraphic sequence provides information on the number of depositional episodes and intervals of stability. The identification of specific soil horizons also provides clues to the degree and duration of soil development, the nature of the soil-forming environment, and the kinds of soil-forming processes that may affect the archaeological record. Further, tracing of soils from exposure to exposure is a key aspect of correlating strata and interpreting the evolution of archaeological landscapes. This chapter presents a discussion of some principals of soil stratigraphy, and the following chapter focuses on the archaeological significance of soils as stratigraphic units. This chapter begins with a discussion of basic stratigraphy, which is one of the fundamental components of field-based geoscience. That section is followed by a closer look at soil stratigraphy, including a summary of both formal and informal soil stratigraphic nomenclature as well as a discussion of the unique characteristics of soils when used as stratigraphic markers and their archaeological implications.