- A surface parallel to the surface of deposition, which may or may not have a physical expression. In shales, for example, the rock splits along planes which are bedding planes, whereas in some sandstones bedding planes are marked by changes of colour, grain size, etc. but no plane of preferred splitting occurs. The original attitude of a bedding plane should not be assumed to have been horizontal. (See also Cross-bedding; Sedimentary structures; Stratigraphic nomenclature.)
- Zone of mechanical weakness that forms in sediment because of slight compositional or textural differences at the interface between adjacent beds.