Chronozone
Encyclopedia
A chronozone or chron is a slice of time that begins at a given identifiable event and ends at another. In the fossil record such tracer events are usually keyed to disappearance (extinction) of a widely distributed and rapidly changing species or the appearance of such a species in the geological record. Chronozones or chrons are used especially in the various disciplines related to geology
, notably in stratigraphy
where relative dating is employed.
There are also events susceptible to identification and analysis by the physical sciences, such as Earth's magnetic field reversals
or the location of a combination of chemical evidence in a layer corresponding to the meteor
strike believed to have caused the extinction
of the dinosaur
s. Hence chronozones, and the international identification and acceptance of a widespread chronozone as an official useful marker or benchmark of time in the rock record, is non-hierarchical in that chronozones do not need to correspond across geographic or geologic boundaries, nor be equal in length (despite an early constraint that one be defined as smaller than a geological stage). A chronozone is usually defined in geologic
terms for a geographical area by fossil names (biozone or biochronozone) or in worldwide terms by geomagnetic reversal
identifiers (polarity chronozone).
According to the International Commission on Stratigraphy
, chronozone is the term used to refer to the rocks formed during the period of time in question, while the word chron refers to that time period. The key factor in designating an internationally acceptable chronozone is whether the overall fossil column is clear, unambiguous, and widespread. Hence, some accepted chronozones contain others, and certain larger chronozones have been designated which span whole define geological time units, both large and small.
For example, the chronozone known as the Reign of Tiberius
(14 to 37 AD) is a subset of the chronozone Imperial Rome
. Similarly the chronozone Pleistocene
is a subset of the chronozone Neogene
.
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, notably in stratigraphy
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
where relative dating is employed.
There are also events susceptible to identification and analysis by the physical sciences, such as Earth's magnetic field reversals
Geomagnetic reversal
A geomagnetic reversal is a change in the Earth's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse...
or the location of a combination of chemical evidence in a layer corresponding to the meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...
strike believed to have caused the extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
of the dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s. Hence chronozones, and the international identification and acceptance of a widespread chronozone as an official useful marker or benchmark of time in the rock record, is non-hierarchical in that chronozones do not need to correspond across geographic or geologic boundaries, nor be equal in length (despite an early constraint that one be defined as smaller than a geological stage). A chronozone is usually defined in geologic
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
terms for a geographical area by fossil names (biozone or biochronozone) or in worldwide terms by geomagnetic reversal
Geomagnetic reversal
A geomagnetic reversal is a change in the Earth's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse...
identifiers (polarity chronozone).
According to the International Commission on Stratigraphy
International Commission on Stratigraphy
The International Commission on Stratigraphy , sometimes referred to by the unofficial "International Stratigraphic Commission" is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigraphy, geological, and geochronological matters on a global...
, chronozone is the term used to refer to the rocks formed during the period of time in question, while the word chron refers to that time period. The key factor in designating an internationally acceptable chronozone is whether the overall fossil column is clear, unambiguous, and widespread. Hence, some accepted chronozones contain others, and certain larger chronozones have been designated which span whole define geological time units, both large and small.
For example, the chronozone known as the Reign of Tiberius
Tiberius
Tiberius , was Roman Emperor from 14 AD to 37 AD. Tiberius was by birth a Claudian, son of Tiberius Claudius Nero and Livia Drusilla. His mother divorced Nero and married Augustus in 39 BC, making him a step-son of Octavian...
(14 to 37 AD) is a subset of the chronozone Imperial Rome
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....
. Similarly the chronozone Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
is a subset of the chronozone Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
.
See also
- Body form
- European Mammal Neogene
- Geologic time scaleGeologic time scaleThe geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
- North American Land Mammal Age
- Fauna (animals)
- Type localityType locality (geology)Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
- List of GSSAa
- List of GSSPs