- Stage (stratigraphy)
chronostratigraphy, a stage is a succession of rock strata laid down in an 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 convention have the same name, and the same boundaries.
Rock series are divided into stages, just as geological epochs are divided into ages. Stages can be divided into smaller stratigraphic units called
chronozones. (See chart at right for full terminology hierarchy.)
The term faunal stage is sometimes used, referring to the fact that the same
fauna(animals) are found throughout the layer (by definition).
Stages are primarily defined by a consistent set of fossils (
biostratigraphy) or a consistent magnetic polarity (see paleomagnetism) in the rock. Usually one or more index fossils that are common, found worldwide, easily recognized, and limited to a single, or at most a few, stages are used to define the stage's bottom.
Thus, for example, in the (still used) local North American subdivision paleontologist finding fragments of the
trilobite"Olenellus" would identify the beds as being from the Waucoban Stagewhereas fragments of a later trilobite such as "Elrathia" would identify the stage as Albertan.
Stages were very important in the 19th and early 20th century as they were the major tool available for dating rock beds until the development of
seismologyand radioactive datingin the second half of the 20th Century. Microscopic analysis of the rock ( petrology) is also sometimes useful in confirming that a given segment of rock is from a particular age.
Originally, faunal stages were only defined regionally; however as additional stratigraphic tools, and especially geochonological ones, were developed, stages were defined over broader and broader areas. More recently, the adjective "faunal" has been dropped as regional and global correlations of rock sequences have become relatively certain and there is less need for faunal labels to define the age of formations. A tendency developed to use European and, to a lesser extent, Asian, stage names for the same time period world wide, even though the faunas in other regions often had little in common with the stage as originally defined.
Boundaries and names are established by the
International Commission on Stratigraphy(ICS) of the International Union of Geological Sciences. As of 2008, the ICS is nearly finished a task begun in 1974, subdividing the Phanerozoic eonotheminto internationally accepted stages using two types of benchmark. For younger stages, a Global Boundary Stratotype Section and Point(GSSP), a physical outcropclearly demonstrates the boundary. For for older stages, a Global Standard Stratigraphic Age(GSSA) is an absolute date. The benchmarks will give a much greater certainty that results can be compared with confidence in the date determinations, and such results will have farther scope than any evaluation based solely on local knowledge and conditions.
In many regions around the world local subdivisions and classification criteria are still used along with the newer internationally coordinated uniform system, but once the research establishes a more complete international system, it is expected that local systems will be abandoned.
tages and lithostratigraphy
Stages can include many lithostratigraphic units (for example formations, beds, members, etc.) of differing rock types that were being laid down in different environments at the same time. In the same way, a lithostratigraphic unit can include a number of stages or parts of them.
European Mammal Neogene
Geologic time scale
North American Land Mammal Age
Type locality (geology)
List of GSSAs
List of GSSPs
Notes and references
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
date = March 2001
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]
* [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)
Wikimedia Foundation. 2010.
Look at other dictionaries:
Illinoian Stage — The Illinoian Stage is the name used by Quaternary geologists in North America to designate middle Pleistocene glacial and interglacial deposits. It precedes the Wisconsin Stage and follows the Pre Illinoian Stage in North America. The Illinoian… … Wikipedia
Pre-Illinoian Stage — The Pre Illinoian Stage is the name currently used for early and middle Pleistocene glacial and interglacial deposits within North America. As the oldest stage in the North American nomenclature, it precedes the Illinoian Stage.Hallberg, G.R.,… … Wikipedia
Hoxnian Stage — The Hoxnian Stage is a middle Pleistocene stage of the geological history of the British Isles. It precedes the Wolstonian Stage and follows the Anglian Stage. The Hoxnian Stage corresponds to the Holstein Interglacial (or Stage ) in northern… … Wikipedia
Anglian Stage — The Anglian Satge is the name for a middle Pleistocene stage used in the British Isles. It precedes the Hoxnian Stage and follows the Cromerian Stage in the British Isles. The Anglian Stage is equivalent to the Elsterian Stage of Europe and… … Wikipedia
Wolstonian Stage — The Wolstonian interglacial is the former name for a middle Pleistocene stage that is now known as the Wolstonian Stage in the British Isles. It precedes the Ipswichian Stage (Eemian Stage in Europe) and follows the Hoxnian Stage in the British… … Wikipedia
Cromerian Stage — The Cromerian Stage is the name for a middle Pleistocene stage used in the in the British Isles that is known as the Cromerian Complex in Europe. It precedes the Anglian Stage and follows the Beestonian Stage in the British Iles. The Cromerian… … Wikipedia
Anglian (stage) — The Anglian Stage is the name for a middle Pleistocene stage used in the British Isles. It precedes the Hoxnian Stage and follows the Cromerian Stage in the British Isles. The Anglian Stage is equivalent to the Elsterian Stage of northern… … Wikipedia
Pre-Pastonian Stage — The Pre Pastonian Stage or Baventian Stage, is the name for an early Pleistocene stage used in the British Isles. It precedes the Pastonian Stage and follows the Bramertonian Stage. This stage ended 1.806 Ma (million years ago) at the end of… … Wikipedia
Pastonian Stage — The Pastonian interglacial, now called the Pastonian Stage, is the name for an early Pleistocene stage used in the British Isles. It precedes the Beestonian Stage and follows the Pre Pastonian Stage. This stage started 1.816 Ma (million years… … Wikipedia
Bramertonian Stage — The Bramertonian Stage is the name for an early Pleistocene stage used in the British Isles. It precedes the Pre Pastonian Stage (Baventian Stage). It derives its name from Bramerton Pits in Norfolk, where the deposits can be found on the surface … Wikipedia