Pedostratigraphy

Abstract

Pedostratigraphy is the study of the stratigraphical and spatial relationships and implications of surface and buried soils. These soils/paleosols occur on landscapes comprising diverse landforms, parent materials, and geomorphic surfaces of different ages formed by erosional and depositional events. A paleosol is a soil, or soil horizon, formed on a landscape of the past (non-buried paleosols are formed in an environment of the past) and they form pedostratigraphic units to be used alongside lithostratigraphic units involving soil parent materials (i.e., geological deposits) and chronostratigraphic units involving time. Pedogenic features that form at the soil surface have different preservation potential when buried. However, recognizable pedogenic features remain which may also imply environment of soil formation including paleoclimate and age. Concepts and application of pedostratigraphy have evolved over time in the scientific literature with some disagreement over nomenclature. However, an important realization in recent years has been that soil formation (i.e., pedogenesis) via top-down processes can continue, even weakly, as geological materials (new parent material) are added incrementally to a stable/metastable land surface. Such pedogenesis is referred to as developmental upbuilding. Many soils on loess or on thin, accumulative (usually distal) tephra-fall deposits, or thin alluvial deposits, for example, are formed this way. Soil formation may be punctuated and re-set, however, by the sudden deposition of a relatively thick geological material that buries the underlying soil, turning the pedogenic clock back to time zero because the buried soil is isolated from surface processes. In this case, pedogenesis via top-down processes begins afresh on the new parent material at the land surface and is referred to as retardant upbuilding. The dynamic-rate model of soil formation takes into account changes in soil environments through time that reflect the interplay of geological and pedological processes, including through upbuilding pedogenesis, to form polygenetic soils (also called compound or multi-layered soils) characterized by stratigraphic (i.e., geological) layering, lithological discontinuities, and buried soil horizons or soils (paleosols).