Lithostratigraphic Unit

Lithostratigraphic units are bodies of rocks in three-dimensional space that are defined based on their observable consistent lithographic properties (or lithologic composition), by the extent of metamorphism or structural characteristics, and by their stratigraphic relationships with the adjacent rock strata. A lithostratigraphic unit may consist of one or more types of sedimentary rocks, extrusive rocks or related metamorphic rocks. The requirement for identifying a unit is the consistency of the rock characteristics. In defining a lithostratigraphic unit, factors such as time, origin, climate, environment or events are not critical factors, but the units themselves are the physical basis for inferring these factors. Lithostratigraphic units are the basic units of geologic mapping, especially in large-scale mapping. They are also primary aspects of regional lithostratigraphy. The customary lithostratigraphic units applicable to a certain geographical area are as follows: (1) Group –...