Chronostratigraphy

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Corresponding units
in chronostratigraphy and
geochronology
Chronostratigraphy geochronology
Aeonothem aeon
Arathem era
system period
series epoch
step Age

The Chronostratigraphy or -grafie ( Greek. Χρόνος chronOS "time") is a sub-discipline of geological stratigraphy . It divides rock bodies according to the age of their formation.

The “basic unit” in the hierarchical system of chronostratigraphy is the level (see box). It is the smallest unit that can be used on a global scale.

definition

In contrast to geochronology , which is an abstract time division, chronostratigraphy is tied to physical rock. For every geochronological unit there is a corresponding chronostratigraphic unit.

The position of chronostratigraphic units within a hierarchy level is always expressed as a top / bottom relationship according to the stratification of the rock. The carbon system is divided into the two series lower carbon and upper carbon. Other systems tend to use adjectives, e.g. B. Lower Jura, Middle Jura, Upper Jura.

Historical development

Characteristic fossils ( key fossils ) enable rocks to be assigned to chronostratigraphic units.

Local - the lithostratigraphy

Within stratigraphy, chronostratigraphy in its pure form is a comparatively young discipline. The oldest form of a stratigraphic structure was introduced in 1669 with the discovery of the stratigraphic principle by Nicolaus Steno . Here, the classification criterion on the basis of which the rock bodies were vertically delimited was the nature of the rock itself. This lithostratigraphic approach to the parallelization of rock bodies proved to be sterile wherever in regionally distant areas the sequence of layers recorded as a reference at one location differed over several rock units.

Supraregional - the biostratigraphy

At the beginning of the 19th century, William Smith discovered the stability of the horizon and the constant vertical sequence of fossils or their socialization and used them stratigraphically to parallel remote, lithologically differently pronounced rocks. This way of working, now called biostratigraphy , took hold during the first half of the 19th century and in many cases led to a supra-regional definition of the formerly local stratigraphic units.

Problems with the global structure

There were further refinements until the middle of the 20th century. So much local data was now available that a global view of the states was possible. The evaluations were difficult, however, because a globally uniform, homogeneous breakdown based on the relative time of the sedimentation of rocks was not available. In addition, the concepts differed; the boundaries were defined partly lithostratigraphically and partly biostratigraphically.

The unease about this situation was articulated, for example, in 1948 during the 18th International Geological Congress in London using the Pliocene / Pleistocene boundary. In 1960 the 21st International Geological Congress in Copenhagen recommended the selection of a profile for this boundary. Another consequence was the establishment of the International Union of Geological Sciences (IUGS) in Paris in 1961 . The IUGS was commissioned to define the concepts and terminology of the stratigraphic disciplines more precisely and to create an internationally standardized classification of the rocks and geological history.

The "new stratigraphy" of the IUGS

The IUGS established the Silurian / Devonian boundary as the first chronostratigraphic boundary . At the same time, the principle was introduced to define chronostratigraphic boundaries by means of a reference profile and a reference point ( GSSP method). The experience gained from this determination was documented in a first edition of the International Stratigraphic Guide in 1976 .

Compared to a description of certain properties, the new method was more objective because it refers to unchangeable and non-interpretable conditions: reference profile and reference point. The transfer to occurrences outside the reference profile then remains subjective. Such a parallelization is only possible with the help of other disciplines (e.g. biostratigraphy or event stratigraphy ).

Advances in science and the development of new processes make it possible today to identify the limits in other outcrops more and more precisely. In the meantime, a considerable proportion of the rocks of the Phanerozoic Era have been structured according to the principles of the “new stratigraphy”.

Chronozone

A chronozone is a body of rock that is defined by another stratigraphic unit outside of chronostratigraphy. For example, a biozone introduced in biostratigraphy defines a biochronozone with the same proper name. This Chronozone includes all rocks that have sedimented in the maximum time span of the Biozone. The same applies to lithostratigraphic, magnetostratigraphic etc. units. The chronozone is a unit that is independent of the chronostratigraphic hierarchy (aeon-theme, ae-theme, system, series and level) and has the unit “chron” as its geochronological equivalent.

Chronostratigraphy versus geochronology

The strict distinction between chronostratigraphy and geochronology is often difficult even for specialist scientists. When is carbon a system , when is it a period? When is the Mesozoic Era , when is it an era theme ? It makes sense to use the same terms when naming rock units and the corresponding periods. The structure projected in a continuous timeline is a simple concept that is also used intuitively by laypeople when dealing with geological layers - the older rocks or layers are below, the younger ones above.

Individual evidence

  1. ↑ FF Steininger & WE Piller: Recommendations (guidelines) for handling the stratigraphic nomenclature. Courier Forschungsinstitut Senckenberg, 209: 1-19, Frankfurt am Main 1999 ZDB-ID 530500-7 .; Page 4.
  2. ^ GB Vai (2001): GSSP, IUGS and IGC: an endless story toward a common language in the Earth sciences. - Episodes, Vol. 24 (1): 29-31; Boulder (Colo.); Page 29
  3. ↑ HD Hedberg (Ed.): International Stratigraphic Guide. - 200 S; J. Wiley, New York 1976.
  4. ↑ ICS 2007: Overview of Global Boundary Stratotype Sections and Points (GSSP's). - As of 2007, International Commission on Stratigraphy. - Link ( memento of June 9, 2007 in the Internet Archive ).
  5. ↑ FF Steininger & WE Piller: Recommendations (guidelines) for handling the stratigraphic nomenclature. Courier Forschungsinstitut Senckenberg, 209: 1-19, Frankfurt am Main 1999 ZDB-ID 530500-7. page 5

literature

  • WA Berggren & JA van Couvering & W. Piller & JA Zalesiewicz & B. McGowran: Chronostratigraphy: Beyond the GSSP. - Penrose Conference, Seggau Castle, Leibnitz, Austria, GSA-Report; 2007. - Link
  • HD Hedberg (Ed.): International Stratigraphic Guide. - 200 S; J. Wiley, New York 1976.
  • ICS 2007: Overview of Global Boundary Stratotype Sections and Points (GSSP's). - As of 2007, International Commission on Stratigraphy. - Link ( Memento from June 9, 2007 in the Internet Archive )
  • A. Salvador: International Stratigraphic Guide (A Guide to Stratigraphic Classification, Terminology and Procedures). 2nd ed., XIX + 214 pp., International Union of Geological Sciences, Geological Society of America, Washington / DC 1994 ISBN 0-8137-7401-2 .
  • St.M. Stanley: Historical Geology. 2nd edition, XIII + 710 pp., Spektrum Akademischer Verlag, Heidelberg & Berlin 2001 ISBN 3-8274-0569-6 .
  • FF Steininger & WE Piller: Recommendations (guidelines) for handling the stratigraphic nomenclature. Courier Forschungsinstitut Senckenberg, 209: 1–19, Frankfurt am Main 1999 ZDB -ID 530500-7 .
  • GB Vai (2001): GSSP, IUGS and IGC: an endless story toward a common language in the Earth sciences. - Episodes, Vol. 24 (1): 29-31; Boulder (Colo.)
  • J. Zalasiewicz & A. Smith & P. ​​Brenchley & J. Evans & R. Knox & N. Riley & A. Gale & FJ Gregory & A. Rushton & Ph. Gibbard & St. Hesselbo & J. Marshall & M. Oates & P. Rawson & N. Trewin: Simplifying the stratigraphy of time. - Geology, Vol. 32 (1): 1-4, 1 tab .; Boulder / Colo. 2004.