chronozone

{{Short description|Unit in chronostratigraphy}}

{{see|Biostratigraphy#Concept of zone|Magnetostratigraphy|Geochronology}}

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.

{{Cite book|editor-last=Salvador |editor-first=Amos |year=1994 |chapter=Chapter 8. Magnetostratigraphic polarity units |title=Stratigraphic Guide |edition=Second (abridged) |publisher=International Commission on Stratigraphy |url=https://stratigraphy.org/guide/magn |archive-url=https://web.archive.org/web/20200612075300/https://stratigraphy.org/guide/magn |archive-date=12 June 2020 |url-status=live }}

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. 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 Press, Cambridge The ICS superseded these earlier usages in 1994.{{Cite magazine|last=Poulson |first=Niels |title=Book Announcement: The Jurassic rocks of Denmark and East Greenland |magazine=International Subcommission on Jurassic Stratigraphy Newsletter |issue=31 |date=August 2004 |pages=27–30, page 29 |url=https://jurassic.stratigraphy.org/files/isjs-newsletter-no-31.pdf |archive-url=https://web.archive.org/web/20210624144918/https://jurassic.stratigraphy.org/files/isjs-newsletter-no-31.pdf |archive-date=24 June 2021 |url-status=live }}

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, and the chronozone Pleistocene is a subset of the chronozone Quaternary.

{{Geology to Paleobiology}}

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