System (stratigraphy)

A system in 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 and stages.

System is in theory equivalent to a geological period- the interval of time itself, but unlike the system of time units, a system in many locations may be interrupted and incomplete. Geologic forces may 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.

Systems in the geological timescale

The systems of the Phanerozoic Eonothem were defined during the 19th century, beginning with the Cretaceous (by Belgian geologist Jean d'Omalius d'Halloy in the Paris Basin) and the Carboniferous (by British geologists William Conybeare and William Phillips) in 1822. The Paleozoic and Mesozoic erathems were divided into the currently used systems before the second half of the 19th century, except for a minor revision when the Ordovician system was added in 1879.

The Cenozoic Era has seen more recent revisions by the International Commission on Stratigraphy. It has been divided into three systems with the Paleogene and Neogene replacing the former Tertiary System though the succeeding Quaternary remains. The one-time system names of Paleocene, Eocene, Oligocene, Miocene and Pliocene are now series within the Paleogene and Neogene.

Another recent development is the official division of the Proterozoic Eonothem into systems, which was decided in 2004.

See also

Multidiscipline comparison

e  h
Units in geochronology and stratigraphy[1]
Segments of rock (strata) in chronostratigraphy Time spans in geochronology Notes to
geochronological units
Eonothem
Eon
4 total, half a billion years or more
Erathem
Era
10 defined, several hundred million years
System
Period
22 defined, tens to ~one hundred million years
Series
Epoch
 tens of millions of years
Stage
Age
 millions of years
Chronozone
Chron
 subdivision of an age, not used by the ICS timescale

External links

Notes

  1. ↑ Cohen, K.M.; Finney, S.; Gibbard, P.L. (2013), International Chronostratigraphic Chart (PDF), International Commission on Stratigraphy.

References