Global Boundary Stratotype Section and Point


Global Boundary Stratotype Section and Point

A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon stratigraphic section which serves as the reference section for a particular boundary 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 2004, 45 of the 96 GSSPs required have been approved.

;An ideal GSSP would
*be accessible to research
*be extensive enough to ensure future access
*be easily related to other exposures worldwide
*contain a radiometrically datable bed at the boundary, and
*include well defined markers at the stage boundary that can be applied worldwide. No GSSP is ideal.

Agreed-upon GSSPs

The Precambrian-Cambrian boundary GSSP at Fortune Head, Newfoundland is a typical GSSP. It is accessible by paved road and is set aside as a nature preserve. A continuous section is available from beds that are clearly Precambrian into beds that are clearly Cambrian. The boundary is set at the first appearance of a complex trace fossil "Trichophycus pedum" that is found worldwide. The Fortune Head GSSP is unlikely to be washed away or built over. Nonetheless, "Trichophycus pedum" is less than ideal as a marker fossil as it is not found in every Cambrian sequence, and it is not assured that it is found at the same level in every exposure. In fact, further eroding its value as a boundary marker, it has since been identified in strata 4m "below" the GSSP! [1] However, no other fossil is known that would be preferable. There is no radiometrically datable bed at the boundary at Fortune Head, but there is one slightly above the boundary in similar beds nearby.These factors have lead some geologists to suggest that this GSSP is in need of re-assigning.

Once a GSSP boundary has been agreed upon, a "golden spike" is driven into the geologic section to mark the precise boundary for future geologists (though in practice the "spike" need neither be golden nor an actual spike). The first stratigraphic boundary was defined in 1977 by identifying the Silurian-Devonian boundary with a bronze plaque at a locality called Klonk, northeast of the village of Suchomastyin in the Czech Republic. GSSPs are also sometimes referred to as Golden Spikes.

GSSAs

Because defining a GSSP depends on finding well-preserved geologic sections and identifying key events, this task becomes more difficult as one goes farther back in time. Before 630 million years ago, boundaries on the geologic timescale are defined simply by reference to fixed dates, known as "Global Standard Stratigraphic Ages".

ee also

Multidiscipline comparison

Related other topics

*Body form
*European Mammal Neogene
*Geologic time scale
**New Zealand geologic time scale
*North American Land Mammal Age
*Fauna (animals)
*Type locality
*List of GSSPs

External links

* [http://www.stratigraphy.org/over.htm The Global Boundary Stratotype Section and Point (GSSP)] : overview
* [http://www.stratigraphy.org/gssp.htm Chart of The Global Boundary Stratotype Sections and Points (GSSP)] : chart

*plainlinks| http://www.rocksandminerals.com/geotime/geotime.htm Geotime chart displaying geologic time periods compared to the fossil record. - Deals with chronology and classifications for laymen (not GSSPs)

Notes and references

References

*Cite journal
last = Gehling
first = James
last2 = Jensen
first2 = Sören
last3 = Droser
first3 = Mary
last4 = Myrow
first4 = Paul
last5 = Narbonne
first5 = Guy
title = Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland
journal = Geological Magazine
volume = 138
issue = 2
pages = 213–218
month = March
year = 2001
url = http://www.journals.cambridge.org/action/displayAbstract?fromPage=online&aid=74669
doi = 10.1017/S001675680100509X
id = 1

* Hedberg, H.D., (editor), "International stratigraphic guide: A guide to stratigraphic classification, terminology, and procedure", New York, John Wiley and Sons, 1976
* [http://www.stratigraphy.org/cheu.pdf International Stratigraphic Chart] from the International Commission on Stratigraphy
* [http://www2.nature.nps.gov/geology/usgsnps/gtime/gtime1.html USA National Park Service]
* [http://astro.wsu.edu/worthey/earth/html/md08.html Washington State University]
* [http://www.ucmp.berkeley.edu/help/timeform.html Web Geological Time Machine]
* [http://www.pballew.net/arithm16.html#aeon Eon or Aeon] , [http://www.pballew.net/etyindex.html Math Words - An alphabetical index]


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