The Natural Context of the Archaeological Record: Landscapes, Sediments, and Soils

Modern landscapes consist of a surface which is shaped by many different types of landforms. Landscapes overlie the Earth’s bedrock. Between the landscape surface and bedrock, is a complex sequence of sediments which were deposited and eroded by various processes. Typically, soils form on these sediments when exposed at the surface and before they are buried. The nature and characteristics of sediments and soils are rarely static. Sediments are affected by various physical and chemical processes and other types of disturbance whether caused by humans, animals, plants, or soil formation. Sediments and soils preserve buried or partially buried archaeological sites contained within these units. If sediments have undergone transformations, it is likely that the archaeological material buried within has been affected to some extent as well.

Stratigraphy studies these layers and determines the chronological sequence of sediments and soils over time. Through field observation, stratigraphic studies place these layers in a relative chronological sequence (i. e., the deepest layers are generally older than overlying layers which are sequentially younger towards the surface). If datable material is found in these layers, then this material can be dated to provide a more absolute chronology for the sequence of layers. Each layer is considered a stratigraphic unit of sediment which was deposited at or over a period of time depending on the rate of deposition. Stratigraphic units are characterized by features such as texture (i. e., percentage of sand, silt, and clay), structure (i. e., which may indicate how the unit was deposited), and mineralogy (i. e., types of minerals present in the sediment). If a stratigraphic unit indicates that it has undergone soil formation, then the unit is further subdivided into soil horizons which are classified by their pedogenic features. Soils are very important to archaeology because soil formation indicates that the surface of a particular stratigraphic unit was once a stable surface. Therefore, the surface was potentially occupied by humans. In addition, soils can be widespread and sometimes they can be correlated with soils in other regions.