A chronozone or chron is a unit in
chronostratigraphy, defined by events such as
geomagnetic reversals (magnetozones), or based on the presence of specific fossils (biozone or biochronozone).
According to the
International Commission on Stratigraphy, the term "chronozone" refers to the rocks formed during a particular time period, while "chron" refers to that time period.
Although non-hierarchical, chronozones have been recognized as useful markers or benchmarks of time in the
rock record. Chronozones are non-hierarchical in that chronozones do not need to correspond across geographic or geologic boundaries, nor be equal in length. Although a former, early constraint required that a chronozone be defined as smaller than a
geological stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by conventi ...
. Another early use ''was'' hierarchical in that Harland ''et al.'' (1989) used "chronozone" for the slice of time smaller than a
faunal stage defined in
biostratigraphy.
[An early use in Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E., Smith, A.G., and Smith, D.G. (1989) ''A Geologic Time Scale'' Cambridge Univ. Press, Cambridge ] The
ICS
ICS may refer to:
Computing
* Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy
* Industrial control system, computer systems and networks used to control industrial plants and infrastructu ...
superseded these earlier usages in 1994.
The key factor in designating an internationally acceptable chronozone is whether the overall fossil column is clear, unambiguous, and widespread. Some accepted chronozones contain others, and certain larger chronozones have been designated which span whole defined geological time units, both large and small.
For example, the chronozone
Pliocene is a subset of the chronozone
Neogene
The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...
, and the chronozone
Pleistocene is a subset of the chronozone
Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
.
See also
*
Body form
A body plan, ( ), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many.
This term, usually applied to animals, envisages a "blueprin ...
*
Chronology (geology)
Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is p ...
*
European Mammal Neogene
*
Geologic time scale
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochrono ...
*
North American Land Mammal Age
*
Type locality (geology)
*
List of GSSPs
References
*
* Hedberg, H.D., (editor), ''International stratigraphic guide: A guide to stratigraphic classification, terminology, and procedure'', New York, John Wiley and Sons, 1976
External links
International Stratigraphic Chartfrom the
International Commission on Stratigraphy
USA National Park Service
overview
chart
{{Chronology
Chronostratigraphy
Geochronology
Geologic time scales
Geology terminology
Geological units
Historical geology
Paleogeography
Paleobiology
Stratigraphy
Units of time