International Commission on Stratigraphy

The International Commission on Stratigraphy (ICS), sometimes referred to by the unofficial name "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 scale.

It is a subordinate body of the International Union of Geological Sciences—of which it is the largest body within the organisation—and of which it is essentially a permanent working subcommittee that meets far more regularly than the quadrennial meetings scheduled by the IUGS, when it meets as a congress or membership of the whole.

International Commission on Stratigraphy
AbbreviationICS
Formation1974
TypeINGO
Region served
Worldwide
Official language
English, French
Parent organization
International Union of Geological Sciences (IUGS)
WebsiteICS Official website

Aims

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 34 defined, tens of millions of years
Stage Age 99 defined, millions of years
Chronozone Chron subdivision of an age, not used by the ICS timescale

One of its main aims, a project begun in 1974, is to establish a multidisciplinary standard and global geologic time scale that will ease paleontological and geobiological comparisons region to region by benchmarks with stringent and rigorous strata criteria called Global Boundary Stratotype Section and Points (GSSPs) within the fossil record. (i.e. section of the rock record as of a core sample section or accessible exposed strata, which when a core sample are usually "trayed" in long pieces, also called "sections" about a meter in length.)

Methodology

Additionally the ICS defines an alternative type of benchmark and criteria called Global Standard Stratigraphic Ages (GSSAs) where the characteristics and dating criteria set solely by physical sciences methods (such as magnetic alignment sequences, radiological criteria, etcetera.) as well as encouraging an international and open debate amongst Earth scientists in the paleontology, geology, geobiology and chronostratigraphy fields, among others.

The International Commission on Stratigraphy has spawned numerous subcommittee level organizations organized and mobilized on a local country-wide or regional basis that are the true working committees of the IUGS, and these do the field work, basis comparisons in conference or co-ordination research committee meetings of local or wide-scale scope.

Publications

The ICS publishes various reports and findings as well as revised references periodically, summarized in the International Stratigraphic Chart, a combined working proposal and guideline-to-date released after the last ICS deliberations prior to the upcoming (next) meeting of the IUGS. Until the IUGS accepts the recommendations, they are unofficial since the IUGS parent approves or dismisses the individual deliberation reports of the ICS, which are presented as recommendations, and span dating and strata selection criteria, and related issues including nomenclatures. In de facto everyday matters, the deliberative results reported out of any meetings of the ICS are widely accepted and immediately enter everyday use, except in the rare cases where they result in a strong body of dissenting opinion, which matters are resolved before the full IUGS.

One such controversy arose in 2009 when the ICS deliberated and decided that the Pliocene Series of the current but unofficially named Quaternary Period should be shifted into the Neogene System and Neogene Period.[2] The term Quaternary has yet to be officially adopted by the IUGS, but has widespread support as acceptable nomenclature for the current geologic period beginning at the GSSP accepted at 5,332,000 years ago at the transition between the Messinian Age to the Zanclean Age (3.6 mya). The ICS voted, perhaps because the time units span human paleo-archaeological strata, to begin the Quaternary at the end GSSP of the Piacenzian Age (2.588 mya) or possibly the end of the Gelasian (1.806 mya), any of which are in a different epoch.

The logo of International Commission on Stratigraphy was designed after the Chinese character of "mountain".

References

  1. ^ Cohen, K.M.; Finney, S.; Gibbard, P.L. (2015), International Chronostratigraphic Chart (PDF), International Commission on Stratigraphy.
  2. ^ Riccardi, A.C. (30 June 2009). "Ratification of the definition of the base of Quaternary System/Period (and top of the Neogene System/Period), and redefinition of the base of the Pleistocene Series/Epoch (and top of the Pliocene Series/Epoch)" (PDF). International Union of Geological Sciences. Retrieved 30 December 2011.

External links

Biozone

Biostratigraphic unit or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa.

A biostratigraphic unit may be defined on the basis of a single taxon or combinations of taxa, on relative abundances of taxa, or variations in features related to the distribution of fossils. The same strata may be zoned differently depending on the diagnostic criteria or fossil group chosen, so there may be several, sometimes overlapping, biostratigraphic units in the same interval.

The length of time represented by a biostratigraphic zone is called a biochron. The International Commission on Stratigraphy defines the following types of Biozones:

Range zones, subdivided into taxon-range zones and concurrent-range zones

Interval zones

Lineage zones

Assemblage Zones

Abundance zones

Cambrian Series 2

Cambrian Series 2 is the unnamed 2nd series of the Cambrian. It lies above the Terreneuvian series and below the Miaolingian. Series 2 has not been formally defined by the International Commission on Stratigraphy, lacking a precise lower boundary and subdivision into stages. The proposed lower boundary is the first appearance of trilobites which is estimated to be around 521 million years ago.

Cambrian Stage 4

Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission on Stratigraphy. One proposal is the first appearance of two trilobite genera, Olenellus or Redlichia. Another proposal is the first appearance of the trilobite species Arthricocephalus chauveaui. Both proposals will set the lower boundary close to 514 million years ago. The upper boundary corresponds to the beginning of the Wuliuan.

Chronozone

Chronozone or chron is a term used for a time interval 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.Identification and acceptance of chronozones as useful markers or benchmarks of time in the rock record, are 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.

An 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.

The ICS has superseded this usage.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.

Geologic time scale

The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. The table of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).

Geological period

A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place.

These periods form elements of a hierarchy of divisions into which geologists have split the Earth's history.

Eons and eras are larger subdivisions than periods while periods themselves may be divided into epochs and ages.

The rocks formed during a period belong to a stratigraphic unit called a system.

Global Boundary Stratotype Section and Point

A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. The effort to define GSSPs is conducted by the International Commission on Stratigraphy, a part of the International Union of Geological Sciences. Most, but not all, GSSPs are based on paleontological changes. Hence GSSPs are usually described in terms of transitions between different faunal stages, though far more faunal stages have been described than GSSPs. The GSSP definition effort commenced in 1977. As of 2012, 64 of the 101 stages that need a GSSP have been formally defined.

Global Standard Stratigraphic Age

In the stratigraphy sub-discipline of geology, a Global Standard Stratigraphic Age, abbreviated GSSA, is a chronological reference point and criterion in the geologic record used to define the boundaries (an internationally sanctioned benchmark point) between different geological periods, epochs or ages on the overall geologic time scale in a chronostratigraphically useful rock layer. A worldwide multidisciplinary effort has been ongoing since 1974 to define such important metrics. The points and strata need be widespread and contain an identifiable sequence of layers or other unambiguous marker (identifiable or quantifiable) attributes.

GSSAs, and the generally more recent and preferred benchmark GSSPs are defined by the International Commission on Stratigraphy (ICS) under the auspices of their parent organization, the International Union of Geological Sciences (IUGS), and are used primarily for time dating of rock layers older than 630 million years ago, lacking a good fossil record. The ICS first attempts to meet the standards of the GSSPs (see below) and if those fail, usually have enough information to make a preliminary selection of several competing GSSA prospects or proposals.

The geologic record becomes spotty prior to about 542 million years ago. This is because the Earth's crust in geological time scales is constantly being recycled by tectonic and weathering forces, and older rocks and especially readily accessible exposed strata that can act as a time calibration are rare.

For more recent periods, a Global Boundary Stratotype Section and Point (GSSP), largely based on paleontology and improved methods of fossil dating, is used to define such boundaries. In contrast to GSSAs, GSSPs are based on important events and transitions within a particular stratigraphic section. In older sections, there is insufficient fossil record or well preserved sections to identify the key events necessary for a GSSP, so GSSAs are defined based on fixed dates and selected criteria.

Greenlandian

In the geologic time scale, the Greenlandian is the earliest age or lowest stage of the Holocene epoch or series, part of the Quaternary. It is one of three subdivisions of the Holocene. The lower boundary of the Greenlandian Age is the GSSP sample from the North Greenland Ice Core Project in central Greenland (75.1000°N 42.3200°W). The Greenlandian GSSP has been correlated with the end of Younger Dryas (from near-glacial to interglacial) and a “shift in deuterium excess values”.The age began 11,700 years prior to the year 2000 (300 HE).The age was officially ratified by the International Commission on Stratigraphy in July 2018 along with the Meghalayan and the Northgrippian.

Holocene

The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years before present, after the last glacial period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene together form the Quaternary period. The Holocene has been identified with the current warm period, known as MIS 1. It is considered by some to be an interglacial period within the Pleistocene Epoch.The Holocene has seen the growth and impacts of the human species worldwide, including all its written history, development of major civilizations, and overall significant transition toward urban living in the present. Human impacts on modern-era Earth and its ecosystems may be considered of global significance for future evolution of living species, including approximately synchronous lithospheric evidence, or more recently hydrospheric and atmospheric evidence of human impacts. In July 2018, the International Union of Geological Sciences split the Holocene epoch into three distinct subsections, Greenlandian (11,700 years ago to 8,326 years ago), Northgrippian (8,326 years ago to 4,200 years ago) and Meghalayan (4,200 years ago to the present), as proposed by International Commission on Stratigraphy. The boundary stratotype of Meghalayan is a speleothem in Mawmluh cave in India, and the global auxiliary stratotype is an ice core from Mount Logan in Canada.The name Holocene comes from the Ancient Greek words ὅλος (holos, whole or entire) and καινός (kainos, new), meaning "entirely recent".

Lethaia

Lethaia is a quarterly peer-reviewed scientific journal of Earth science, covering research on palaeontology and stratigraphy. Now published by Wiley-Blackwell, it was originally published by the International Commission on Stratigraphy. It is an official publication of the International Palaeontological Association and the International Commission on Stratigraphy. The journal had a 2012 impact factor of 2.488, ranking it 7th out of 48 journals in the category "Paleontology", though its IF has since declined.

Lopingian

The Lopingian is the uppermost series/last epoch of the Permian. It is the last epoch of the Paleozoic. The Lopingian was preceded by the Guadalupian and followed by the Early Triassic.

The name was introduced by Amadeus William Grabau in 1931 and derives from Leping, Jiangxi in the then Republic of China. It consists of two stages/ages. The earlier is the Wuchiapingian and the later is the Changhsingian.The International Chronostratigraphic Chart (v2018/07) provides a numerical age of 259.1 ±0.5 Ma. If a Global Boundary Stratotype Section and Point (GSSP) has been approved, the lower boundary of the earliest stage determines numerical age of an epoch. The GSSP for the Wuchiapingian has a numerical age of 259.8 ± 0.4 Ma.The Lopingian ended with the Permian–Triassic extinction event.

Meghalayan

In the geologic time scale, the Meghalayan is the latest age or uppermost stage of the Quaternary. It is also the upper, or latest, of three subdivisions of the Holocene epoch or series. Its Global Boundary Stratotype Section and Point (GSSP) is a Mawmluh cave formation in Meghalaya, northeast India. Mawmluh cave is one of the longest and deepest caves in India, and conditions here were suitable for preserving chemical signs of the transition in ages. The global auxiliary stratotype is an ice core from Mount Logan in Canada.The Meghalayan begins 4,200 years BP, i.e., before 1950 (c. 2250 BCE or 7750 HE), leaving open room for the possible creation of the Anthropocene from 1950 forward. The age began with a 200-year drought that impacted human civilizations in Egypt, Greece, Syria, Canaan, Mesopotamia, the Indus Valley and the Yangtze River Valley. "The fact that the beginning of this age coincides with a cultural shift caused by a global climate event makes it unique," according to Stanley Finney, Secretary General of the International Union of Geological Sciences.The age was officially ratified by the International Commission on Stratigraphy in July 2018 along with the Greenlandian and the Northgrippian.

Middle Pleistocene

The Middle Pleistocene is a subdivision of the Pleistocene Epoch, from 781,000 to 126,000 years ago (781–126 ka). It is preceded by the Calabrian stage, beginning with the Brunhes–Matuyama reversal, and succeeded by the Tarantian stage (equivalent ot the Late or Upper Pleistocene), taken as beginning with the last interglacial (MIS 5).

The tripartite subdivision of the Pleistocene into Lower (Early), Middle and Upper (Late) has been in use since the 1930s.

It is in use as a provisional or "quasi-formal" designation by the International Union of Geological Sciences (IUGS) as of 2018,

pending the ratification of the 2017 proposal by the International Commission on Stratigraphy (Subcommission on Quaternary Stratigraphy, ICSSQS) of a Chibanian stage.The Middle Pleistocene contains the transition from the Lower to Middle Paleolithic in palaeoanthropology, i.e. the emergence transition from Homo erectus to Homo sapiens. The oldest known human's DNA dates to the Middle Pleistocene.

Northgrippian

In the geologic time scale, the Northgrippian is the middle of the three ages of the Holocene epoch which lies in the Quaternary period. It was officially ratified by the International Commission on Stratigraphy in July 2018 along with the Greenlandian and the Meghalayan.The age began 8,236 years prior to the year 2000 (6236 BCE or 3764 HE), and goes up to the start of the Meghalayan, which began 4,200 years prior to the year 1950 (2250 BCE or 7750 HE).

Preboreal

The Preboreal is a stage of the Holocene epoch. It is preceded by the Tarantian and succeeded by the Boreal. It lasted from 10,300 to 9,000 BP in radiocarbon years or 8350 BC to 7050 BC in Gregorian calendar years (8th millennium BC). It is the first stage of the Holocene epoch.

The Holocene has not been formally divided by the IUGS. As a result the Preboreal is only a proposal, and as stratigraphy and dating techniques have improved since this 1972 proposal the dates would be different if proposed today. Instead others have begun to use the terms Early, Middle and Late, which strictly should be Lower, Middle and Upper for the Holocene. If this terminology were to be used the preboreal would be replaced by Lower Holocene which would be dated 11.7 - 8.2 ka B2K.In July 2018 the International Commission on Stratigraphy ratified Greenlandian as the globally recognised first age of the Holocene, much overlapping with the North European regional term Preboreal.

Quaternary

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 2.588 ± 0.005 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.588 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today). The informal term "Late Quaternary" refers to the past 0.5–1.0 million years.The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets associated with Milankovitch cycles and the associated climate and environmental changes that occurred.

Terreneuvian

The Terreneuvian is the lowermost and oldest series of the Cambrian geological system. Its base is defined by the first appearance datum of the trace fossil Treptichnus pedum around 541 million years ago. Its top is defined as the first appearance of trilobites in the stratigraphic record around 521 million years ago. This series was formally ratified by the International Commission on Stratigraphy in 2012.The Fortunian stage and presently unnamed Cambrian Stage 2 are the stages within this series. The Terreneuvian corresponds to the pre-trilobitic Cambrian.The name Terreneuvian is derived from Terre Neuve, a French name for the island of Newfoundland, Canada, where many rocks of this age are found, including the type section.

Tertiary

Tertiary is a widely used term for the geologic period from 66 million to 2.6 million years ago, a timespan that occurs between the Mesozoic Era and the Quaternary, although no longer recognized as a formal unit by the International Commission on Stratigraphy. The span of the Tertiary is subdivided into the Paleocene Epoch (56 – 66 million years BP), the Eocene Epoch (33.9 – 56 million years BP), the Oligocene Epoch (23 – 33.9 million years BP), the Miocene Epoch (5.3 – 23 million years BP) and the Pliocene Epoch (2.6 – 5.3 million years BP), extending to the first stage of the Pleistocene Epoch, the Gelasian stage.The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start of the Cenozoic Era, and extended to the beginning of the Quaternary glaciation at the end of the Pliocene Epoch.

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