chronostratigraphy
Chronostratigraphy is the branch of stratigraphy that studies the ages of rock strata in relation to time.
The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geologic ...
, defined by events such as
geomagnetic reversal
A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south). The Earth's field has alternated ...
s (magnetozones), or based on the presence of specific fossils (biozone or biochronozone).
According to the
International Commission on Stratigraphy
The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...
, 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
The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata. That is, deposits laid down by volcanism or by deposition of sediment derived from weathering detritus (clays, sand ...
. 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
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 convent ...
defined in
biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of B ...
.
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.
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
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Neogene, and the chronozone
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
European Mammal Neogene
European, or Europeans, or Europeneans, may refer to:
In general
* ''European'', an adjective referring to something of, from, or related to Europe
** Ethnic groups in Europe
** Demographics of Europe
** European cuisine, the cuisines of Europe a ...
*
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 geochr ...
*
North American Land Mammal Age
The North American land mammal ages (NALMA) establishes a geologic timescale for North American fauna beginning during the Late Cretaceous and continuing through to the present. These periods are referred to as ages or intervals (or stages when re ...
*
Type locality (geology)
Type locality, also called type area, is the locality where a particular rock type, stratigraphic unit or mineral species is first identified. If the stratigraphic unit in a locality is layered, it is called a stratotype, whereas the standard ...
*
List of GSSPs
This is a list of Global Boundary Stratotype Sections and Points. Since 1977, Global Boundary Stratotype Sections and Points (abbreviated GSSPs) are internationally agreed upon reference points on stratigraphic sections of rock which define the ...
References
*
* Hedberg, H.D., (editor), ''International stratigraphic guide: A guide to stratigraphic classification, terminology, and procedure'', New York, John Wiley and Sons, 1976
International Commission on Stratigraphy
The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...