GSSP

A **GSSP**, more fully a **Global Boundary Stratotype Section and Point**,  is an internationally agreed point which defines the start of a stage on the geologic time scale.

The work is done by the International Commission on Stratigraphy, a part of the International Union of Geological Sciences. As of 2012, 64 of the 101 stages that need a GSSP have been decided.

## Rules for GSSP

A geologic section has to follow the rules to be adapted as a GSSP by the ICS. The list below are the rules:

- A GSSP has to decide the lower boundary (start of a geological period) of a geologic stage.
- The lower boundary (start of a geological period) has to be decided using a primary (main) marker (usually first appearance datum of a fossil specie).
    - There should also be secondary markers (other fossils, chemical, geomagnetic reversal).
    - The horizon in which the marker appears should have minerals that can be radiometrically dated.
    - The marker has to have regional and global correlation in outcrops of the same age
    - The marker should be independent of facies.
- The outcrop has to have an acceptable thickness
- Sedimentation has to be constant without any changes in facies
- The outcrop should not be affected by tectonic and sedimentary movements, and metamorphism
- The outcrop has to be accessible to research and free to access.
    - This includes that the outcrop has to be located where it can be visited quickly (International airport and good roads), has to be kept in good condition (Ideally a national reserve), in accessible terrain, extensive enough to allow repeated sampling and open to researchers of all nationalities.

## List

This list shows some of the GSSPs.

|style="width:75px;"|Period|style="width:75px;"|Epoch|style="width:55px;"|Age (mya)|width="15px;"|Status|style="width:200px;"|GSSP location|width=""|Defining markers|width=""|Geographic Coordinates|width=""|References|
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|colspan="8"|Phanerozoic|||||||||||||||
|colspan="8"|Cainozoic|||||||||||||||
|rowspan="3"|Quaternary|||||||||||||||
|Holocene|0.117||NGRIP2 ice core, Greenland|* End of the Younger Dryas stadial (cold stage)||||||||||||
|Pleistocene|2.588||Monte San Nicola Section, Sicily, Italy|* Base of magnetic polarity chronozone C2r (Matuyama). * Extinction of _Discoaster pentaradiatus_ and _Discoaster surculus_ (Calcareous nannofossil).||||||||||||
|rowspan="3"|Neogene|||||||||||||||
|Pliocene|5.333||Heraclea Minoa section Heraclea Minoa, Sicily, Italy|* Top of magnetic polarity chronozone C3r. * First appearance of _Ceratolithus acutus_ and near extinction of _Triquetrorhabdulus rugosus_ (Calcareous nannofossil).||||||||||||
|Miocene|23.03||Lemme-Carrosio Section, Carrosio, Italy|* Base of magnetic polarity chronozone C6Cn.2n. * Near first appearance of _Paragloborotalia kugleri_ (Planktonic foraminifera).||||||||||||
|rowspan="4"|Palaeogene|||||||||||||||
|Oligocene|33.9||Massignano Section, Massignano, Ancona, Italy|* Extinction of _Hantkenina_ and _Cribrohantkenina_ (Planktonic foraminifera).||||||||||||
|Eocene|56||Dababiya section, Luxor, Egypt|* Base of negative Carbon Isotope Excursion (CIE).||||||||||||
|Palaeocene|66||El Kef Section, El Kef, Tunisia|* Iridium enriched layer associated with a major meteorite impact and subsequent extinction event.||||||||||||
|colspan="8"|Mesozoic|||||||||||||||
|rowspan="3"|Cretaceous|||||||||||||||
|Upper Cretaceous|100.5||Mont Risoux, Hautes-Alpes, France|* First appearance of _Rotalipora globotruncanoides_ (Planktonic foraminifera)||||||||||||
|Lower Cretaceous|145|||Candidates: *Magnetic—base of Chron M18r *Base of Calpionellid zone B||||||||||||
|rowspan="4"|Jurassic|||||||||||||||
|Upper Jurassic|163.5||Candidate sections: * Redcliff Point, Dorset, England * Savouron, Provence, France|* Horizon of _Cardioceras redcliffense_ (Ammonite).||||||||||||
|Middle Jurassic|174.1||Fuentelsaz, Spain|* First appearance of _Leioceras opalinum_ and _Leioceras lineatum_ * Biologic: First appearance of genus _Leioceras_ (Ammonite).||||||||||||
|Lower Jurassic|201.3||Kuhjoch section, Karwendel mountains, Northern Calcareous Alps, Austria|* Near first appearance of smooth _Psiloceras spela_ group (Ammonite).||||||||||||
|rowspan="4"|Triassic|||||||||||||||
|Upper Triassic|235||Prati di Stuores, Dolomites, Italy|* First appearance of _Daxatina canadensis_ (Ammonite). * Near first appearance of _Metapolygnathus polygnathiformis_ (Conodont). * Above magnetic zone S2n.||||||||||||
|Middle Triassic|247.2||Candidate sections: * Desli Caira, Dobrogea, Romania * Guandao, Guizhou, China|* First appearance of _Chiosella timorensis_ (Conodont). * Magnetic: Base of magnetic zone MT1n.||||||||||||
|Lower Triassic|252.2||Meishan, Zhejiang, China|* First appearance of _Hindeodus parvus_ (Conodont).||||||||||||
|colspan="8"|Palaeozoic|||||||||||||||
|colspan="2"|Permian|298.9||Aidaralash, Ural Mountains, Kazakhstan|* First appearance of _Streptognathodus isolatus_ within the morphotype _Streptognathodus wabaunsensis_ chronocline (Conodont).|||||||||||
|rowspan="3"|Carboniferous|||||||||||||||
|Pennsylvanian|323.2||Arrow Canyon, Nevada, USA|* First appearance of _Declinognathodus nodiliferus_ (Conodont).||||||||||||
|Mississippian|358.9||La Serre, Montagne Noire, France|* First appearance of _Siphonodella sulcata_ (Conodont). * In 2006 it was discovered that this GSSP has biostratigraphic problems.||||||||||||
|colspan="2"|Devonian|419.2||Klonk, Prague, Czech Republic|* First appearance of _Monograptus uniformis_ (graptolite).|||||||||||
|colspan="2"|Silurian|443.4||Dob's Linn, Moffat, U.K.|* First appearance of _Akidograptus ascensus_ and _Parakidograptus acuminatus_ (Graptolite). * 1.6 m above the base of the Birkhill Shale Formation.|||||||||||
|colspan="2"|Ordovician|485.4||Greenpoint section Green Point, Newfoundland, Canada|* First appearance of _Iapetognathus fluctivagus_ (Conodont). * Planktonic graptolites occur 4.8 m above boundary. * Coincides with a peak in carbon isotopes.|||||||||||
|colspan="2"|Cambrian|541||Fortune head section, Newfoundland, Canada|* First appearance of _Treptichnus pedum_ (trace fossil).|||||||||||
|colspan="6"|Precambrian|||||||||||||||
|colspan="8"|Proterozoic|||||||||||||||
|rowspan="4"|Neoproterozoic|||||||||||||||
|Ediacaran|635||Enorama Creek section Flinders Ranges, South Australia|* Worldwide distinct cap carbonates. * Beginning of a distinctive pattern of secular changes in carbon isotopes.||||||||||||
|Cryogenian|850||Defined chronometrically now. GSSP is in progress.|||||||||||||
|Tonian|1000||Defined chronometrically|||||||||||||
|rowspan="4"|Mesoproterozoic|||||||||||||||
|Stenian|1200||Defined chronometrically|||||||||||||
|Ectasian|1400||Defined chronometrically|||||||||||||
|Calymmian|1600||Defined chronometrically|||||||||||||
|rowspan="5"|Palaeoproterozoic|||||||||||||||
|Statherian|1800||Defined chronometrically|||||||||||||
|Orosirian|2050||Defined chronometrically|||||||||||||
|Rhyacian|2300||Defined chronometrically|||||||||||||
|Siderian|2500||Defined chronometrically|||||||||||||
|colspan="8"|Archaean & Hadean|||||||||||||||
|colspan="2"|Neoarchaean|2800||||||||||||||
|colspan="2"|Mesoarchaean|3200||||||||||||||
|colspan="2"|Palaeoarchaean|3600||||||||||||||
|colspan="2"|Eoarchaean|4000||||||||||||||
|colspan="2"|Hadean|4567||||||||||||||

## Global Standard Stratigraphic Age (GSSAs)

Because defining a GSSP depends on finding well-preserved geologic sections and identifying key events, this task becomes more harder as one goes farther back in time.  Before 640 million years ago, boundaries on the geologic timescale are defined simply by reference to fixed dates, known as "Global Standard Stratigraphic Ages". The oldest GSSP is the one that marks the start of the Ediacaran at 635 million years ago.