System (stratigraphy)

System (stratigraphy)

A system in the natural sciences and stratigraphy is an idealized composite unit of the geologic record made up of a succession of rock layers that were laid down together within the corresponding geological period. The system is thus a unit of the geologic record or rock column, pieced together using the Law of Superposition and mapped to its corresponding period— the associated continuous chronostratigraphical time unit, a relative metric that science committees have determined solid dating for as organized on the geologic time scale. A system is therefore a unit of chronostratigraphy, unrelated to lithostratigraphy, which subdivides rock layers on their lithology. Systems are subdivisions of erathems and are themselves divided into series, epochs and stages.

System is a term defining a unit of rocklayers formed in a certain time interval; it is in theory equivalent to the term period defining the interval of time itself, but unlike the system of time units, a system in many locations may be interrupted and incomplete as geologic forces alternately uplift or depress a region, bend the landscape and so expose a terrain feature once accumulating rock to weathering and vice versa. The overall rock record has been piecewise constructed throughout each physical system, series, et al. using superposition, and is treated in practice as one large continuous rock column, the whole matching the corresponding period. For this reason, the two words are sometimes confused in informal literature.