Phillips,J.D. and Lorz,C.(2008): Origins and implications of soil layering. Earth-Science Reviews, 89, 144-155.


 Layering is common in soils, due to a variety of pedologic and geologic processes, and had important consequences for the interpretation of soils and landscapes. Layering can derive from original sedimentary layering; depositional upbuilding; episodic surface erosion, deposition, and stability; soil production by weathering; vertical or lateral translocation; bioturbation; and various combinations of these. Complex and polygenetic models incorporate both genetic and pedogenic processes, and allow for physical and biological processes, as well as both vertical and horizontal movements. We review these conceptual frameworks and synthesize them into a vertical contrast model (VCM) for interpreting layered surficial materials. The VCM incorporates a variety of geologic and pedologic processes which may create, destroy, enhance, or obscure vertical contrasts. The model is illustrated via application to sites in the Ouachita Mountains, USA, and northwest Saxonian Lowlands, Germany. The examples illustrate the importance of a comprehensive pedogeomorphic interpretation of layering, since neither standard stratigraphic or top-down pedogenic principles necessarily apply. The examples also show that the same process can, sometimes contemporaneously, both create and destroy vertical contrasts.

Keywords: layering; horizonation; soils; regolith; pedogenesis; surficial deposits; geoarchaeology 』

1. Introduction
 1.1. Soil layering
 1.2. Definitions
2. Origins of layering
 2.1. Simple conceptual models
 2.2. Complex and polygenetic models
 2.3. Vertical contrast model
3. Ouachita Mountains, Arkansas, USA
 3.1. Geomorphological interpretation of layering
 3.2. Effects of tree uprooting on layering
 3.3. Rate of layering
 3.4. Archaeological materials
4. Northwest Saxonian Lowlands, Germany
 4.1. Geomorphic setting
 4.2. Layering and vertical texture contrasts
5. Discussion and conclusions