Principal Kinds of Chronosequences and Their Significance in Soil History

Summary There are four principal kinds of chronosequences of soils that differ in age. These sequences have different combinations of isochrony and/or time‐transgression of incipience and cessation of development of their encompassed soil members. A further criterion is the presence or absence of partial overlap in the history of these members. Post‐incisive sequences have been commonly used for inferences on pathways and rates of development of individual soils, but their usual interpretation relies on the assumption that all soils involved developed the same way even while some of them may be polygenetic. Theoretically, pre‐incisive sequences are to be preferred because they should provide time‐lapse information on soil development. But, since they necessarily involve buried soils, problems of post‐burial change may complicate their interpretation. The usefulness of fully time‐transgressive sequences with partially overlapping soil tory depends on their predominant pre‐incisive or post‐incisive character. Fully time‐transgressive chronosequences without overlap of soil history may provide insight into regimes of soil development throughout geologic time, but not into rates of change of individual soils. Functional soil‐landscape units, such as catenas and valley basins may have internal soil age differentiation. This imposes restrictions on the systematic investigation of their evolution.