Chronostratigraphy: Difference between revisions
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{{Short description|Branch of stratigraphy that studies the ages of rock strata in relation to time}} |
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'''Chronostratigraphy''' is the branch of [[stratigraphy]] that studies the ages of rock [[stratum|strata]] in relation to [[time]]. |
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The ultimate aim of chronostratigraphy is to arrange the sequence of [[Deposition (geology)|deposition]] and the time of deposition of all rocks within a [[Geology|geological]] region, and eventually, the entire geologic record of the [[Earth]]. |
The ultimate aim of chronostratigraphy is to arrange the sequence of [[Deposition (geology)|deposition]] and the time of deposition of all rocks within a [[Geology|geological]] region, and eventually, the entire geologic record of the [[Earth]]. |
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The standard stratigraphic [[nomenclature]] is a chronostratigraphic system based on [[Paleontology|palaeontological]] intervals of time defined by recognised [[fossil]] assemblages ([[biostratigraphy]]). The aim of chronostratigraphy is to give a meaningful [[geochronology|age date]] to these fossil assemblage intervals and interfaces.{{ |
The standard stratigraphic [[nomenclature]] is a chronostratigraphic system based on [[Paleontology|palaeontological]] intervals of time defined by recognised [[fossil]] assemblages ([[biostratigraphy]]). The aim of chronostratigraphy is to give a meaningful [[geochronology|age date]] to these fossil assemblage intervals and interfaces.<ref>{{Cite web|author=Subcommission on Quaternary Stratigraphy |year=2002 |title=Chronostratigraphy |publisher=[[International Commission on Stratigraphy]] (ICS) |url=http://quaternary.stratigraphy.org/stratigraphic-guide/chronostratigraphy/ |archive-url=https://web.archive.org/web/20180728055721/http://quaternary.stratigraphy.org/stratigraphic-guide/chronostratigraphy/ |archive-date=28 July 2018 |url-status=live }}</ref> |
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== Methodology == |
== Methodology == |
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Chronostratigraphy relies heavily upon [[isotope geology]] and [[geochronology]] to derive hard dating of known and well defined rock units which contain the specific fossil assemblages defined by the stratigraphic system. In practice, as it is very difficult to [[Radiometric dating|isotopically]] date most fossils and [[ |
Chronostratigraphy relies heavily upon [[isotope geology]] and [[geochronology]] to derive hard dating of known and well defined rock units which contain the specific fossil assemblages defined by the stratigraphic system. In practice, as it is very difficult to [[Radiometric dating|isotopically]] date most fossils and [[sedimentary rock]]s directly, inferences must be made in order to arrive at an age date which reflects the beginning of the interval. |
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The [[methodology]] used is derived from the [[law of superposition]] and the principles of [[cross-cutting relationships]]. |
The [[methodology]] used is derived from the [[law of superposition]] and the principles of [[cross-cutting relationships]]. |
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Because [[igneous]] rocks occur at specific intervals in time and are essentially instantaneous on a geologic time scale, and because they contain [[mineral]] assemblages which may be dated more accurately and precisely by isotopic methods, the construction of a chronostratigraphic column relies heavily upon [[Intrusive rock|intrusive]] and [[Extrusive rock|extrusive]] igneous rocks. |
Because [[igneous]] rocks occur at specific intervals in time and are essentially instantaneous on a geologic time scale, and because they contain [[mineral]] assemblages which may be dated more accurately and precisely by isotopic methods, the construction of a chronostratigraphic column relies heavily upon [[Intrusive rock|intrusive]] and [[Extrusive rock|extrusive]] igneous rocks. |
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[[Metamorphism]], often associated with [[Fault (geology)|faulting]], may also be used to bracket depositional intervals in a chronostratigraphic column. Metamorphic rocks can occasionally be dated, and this may give some |
[[Metamorphism]], often associated with [[Fault (geology)|faulting]], may also be used to bracket depositional intervals in a chronostratigraphic column. Metamorphic rocks can occasionally be dated, and this may give some limitations to the [[Age (geology)|age]] in which a bed could have been laid down. For example, if a bed containing [[Graptolithina|graptolites]] overlies [[crystal]]line [[Basement (geology)|basement]] at some point, dating the crystalline basement will give a maximum age of that fossil assemblage. |
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This process requires a considerable degree of effort and checking of field relationships and age dates. For instance, there may be many millions of years between a bed being laid down and an intrusive rock cutting it; the estimate of age must necessarily be between the oldest cross-cutting intrusive rock in the fossil assemblage and the youngest rock upon which the fossil assemblage rests. |
This process requires a considerable degree of effort and checking of field relationships and age dates. For instance, there may be many millions of years between a bed being laid down and an intrusive rock cutting it; the estimate of age must necessarily be between the oldest cross-cutting intrusive rock in the fossil assemblage and the youngest rock upon which the fossil assemblage rests. |
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== Units == |
== Units == |
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Chronostratigraphic units, with examples:<ref name=Jackson>{{ |
Chronostratigraphic units, with examples:<ref name=Jackson>{{Cite book|editor-last=Jackson |editor-first=Juia A. |year=1997 |title=Glossary of Geology |edition=4th |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=978-0-922152-34-6 }}</ref> |
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*eonothem – [[Phanerozoic]] |
*eonothem – [[Phanerozoic]] |
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*erathem – [[Paleozoic]] |
*erathem – [[Paleozoic]] |
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== Differences from geochronology == |
== Differences from geochronology == |
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It is important not to confuse geochronologic and chronostratigraphic units.<ref name= |
It is important not to confuse geochronologic and chronostratigraphic units.<ref>{{Cite book|last=Schoch |first=Robert M. |year=1989 |title=Stratigraphy: Principles and Methods |location=New York |publisher=Van Nostrand Reinhold |page=351 |isbn=978-0-442-28021-5 }}</ref><ref name=Fastovsky&Weishampel>{{Cite book|last1=Fastovsky |first1=David E. |last2=Weishampel |first2=David B. |year=1996 |title=The Evolution and Extinction of the Dinosaurs |location=Cambridge, England |publisher=Cambridge University Press |pages=22–23 |isbn=978-0-521-44496-5 }}</ref> Chronostratigraphic units are geological material, so it is correct to say that fossils of the species ''[[Tyrannosaurus|Tyrannosaurus rex]]'' have been found in the Upper Cretaceous Series.<ref name="giantsauropod">{{Cite journal|last1=Smith |first1=Joshua B. |last2=Lamanna |first2=Matthew C. |last3=Lacovara |first3=Kenneth J. |last4=Dodson | first4=Peter Jr. |last5=Poole |first5=Jason C. |last6=Smith |first6=Jennifer R. |last7= Giegengack |first7=Robert |last8=Attia |first8=Yousry |year=2001 |title=A Giant Sauropod Dinosaur from an Upper Cretaceous Mangrove Deposit in Egypt |journal=Science |volume=292 |issue=5522 |pages=1704–1706 |doi=10.1126/science.1060561 |issn=1095-9203 |pmid=11387472 |bibcode=2001Sci...292.1704S |s2cid=33454060 |url=http://doc.rero.ch/record/14792/files/PAL_E1924.pdf }}</ref> Geochronological units are periods of time and take the same name as standard stratigraphic units but replacing the terms upper/lower with late/early. Thus it is also correct to say that ''Tyrannosaurus rex'' lived during the [[Late Cretaceous]] Epoch.<ref name="ICSchronostrat">{{Cite book|editor-last=Salvador |editor-first=Amos |year=1994 |chapter=Chapter 9. Chronostratigraphic Units |title=Stratigraphic Guide |edition=Second (abridged) |publisher=International Commission on Stratigraphy |url=https://stratigraphy.org/guide/chron |archive-url=https://web.archive.org/web/20200612075254/https://stratigraphy.org/guide/chron |archive-date=12 June 2020 |url-status=live }}</ref> |
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Chronostratigraphy is an important branch of stratigraphy because the age correlations derived are crucial |
Chronostratigraphy is an important branch of stratigraphy because the age correlations derived are crucial in drawing accurate cross sections of the spatial organization of rocks and in preparing accurate paleogeographic reconstructions. |
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==See also== |
==See also== |
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* [[Geologic record]] |
* [[Geologic record]] |
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* [[Geologic time scale]] |
* [[Geologic time scale]] |
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* [[Isotope geology]] |
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* [[List of geochronologic names]] |
* [[List of geochronologic names]] |
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* [[Stratigraphy]] |
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* [[Tectonostratigraphy]] |
* [[Tectonostratigraphy]] |
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==References== |
==References== |
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{{ |
{{Reflist}} |
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{{Chronology}} |
{{Chronology}} |
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{{Authority control}} |
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[[Category:Chronostratigraphy| ]] |
[[Category:Chronostratigraphy| ]] |
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Latest revision as of 19:04, 2 March 2024
Chronostratigraphy is the branch of stratigraphy that studies the ages of rock strata in relation to time.
The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of the Earth.
The standard stratigraphic nomenclature is a chronostratigraphic system based on palaeontological intervals of time defined by recognised fossil assemblages (biostratigraphy). The aim of chronostratigraphy is to give a meaningful age date to these fossil assemblage intervals and interfaces.[1]
Methodology
[edit]Chronostratigraphy relies heavily upon isotope geology and geochronology to derive hard dating of known and well defined rock units which contain the specific fossil assemblages defined by the stratigraphic system. In practice, as it is very difficult to isotopically date most fossils and sedimentary rocks directly, inferences must be made in order to arrive at an age date which reflects the beginning of the interval.
The methodology used is derived from the law of superposition and the principles of cross-cutting relationships.
Because igneous rocks occur at specific intervals in time and are essentially instantaneous on a geologic time scale, and because they contain mineral assemblages which may be dated more accurately and precisely by isotopic methods, the construction of a chronostratigraphic column relies heavily upon intrusive and extrusive igneous rocks.
Metamorphism, often associated with faulting, may also be used to bracket depositional intervals in a chronostratigraphic column. Metamorphic rocks can occasionally be dated, and this may give some limitations to the age in which a bed could have been laid down. For example, if a bed containing graptolites overlies crystalline basement at some point, dating the crystalline basement will give a maximum age of that fossil assemblage.
This process requires a considerable degree of effort and checking of field relationships and age dates. For instance, there may be many millions of years between a bed being laid down and an intrusive rock cutting it; the estimate of age must necessarily be between the oldest cross-cutting intrusive rock in the fossil assemblage and the youngest rock upon which the fossil assemblage rests.
Units
[edit]Chronostratigraphic units, with examples:[2]
- eonothem – Phanerozoic
- erathem – Paleozoic
- system – Ordovician
- series – Upper Ordovician
- stage – Ashgill
Differences from geochronology
[edit]It is important not to confuse geochronologic and chronostratigraphic units.[3][4] Chronostratigraphic units are geological material, so it is correct to say that fossils of the species Tyrannosaurus rex have been found in the Upper Cretaceous Series.[5] Geochronological units are periods of time and take the same name as standard stratigraphic units but replacing the terms upper/lower with late/early. Thus it is also correct to say that Tyrannosaurus rex lived during the Late Cretaceous Epoch.[6]
Chronostratigraphy is an important branch of stratigraphy because the age correlations derived are crucial in drawing accurate cross sections of the spatial organization of rocks and in preparing accurate paleogeographic reconstructions.
See also
[edit]- Biostratigraphy
- Chronozone
- Geochronology
- Geologic record
- Geologic time scale
- List of geochronologic names
- Tectonostratigraphy
References
[edit]- ^ Subcommission on Quaternary Stratigraphy (2002). "Chronostratigraphy". International Commission on Stratigraphy (ICS). Archived from the original on 28 July 2018.
- ^ Jackson, Juia A., ed. (1997). Glossary of Geology (4th ed.). Alexandria, Virginia: American Geological Institute. ISBN 978-0-922152-34-6.
- ^ Schoch, Robert M. (1989). Stratigraphy: Principles and Methods. New York: Van Nostrand Reinhold. p. 351. ISBN 978-0-442-28021-5.
- ^ Fastovsky, David E.; Weishampel, David B. (1996). The Evolution and Extinction of the Dinosaurs. Cambridge, England: Cambridge University Press. pp. 22–23. ISBN 978-0-521-44496-5.
- ^ Smith, Joshua B.; Lamanna, Matthew C.; Lacovara, Kenneth J.; Dodson, Peter Jr.; Poole, Jason C.; Smith, Jennifer R.; Giegengack, Robert; Attia, Yousry (2001). "A Giant Sauropod Dinosaur from an Upper Cretaceous Mangrove Deposit in Egypt" (PDF). Science. 292 (5522): 1704–1706. Bibcode:2001Sci...292.1704S. doi:10.1126/science.1060561. ISSN 1095-9203. PMID 11387472. S2CID 33454060.
- ^ Salvador, Amos, ed. (1994). "Chapter 9. Chronostratigraphic Units". Stratigraphic Guide (Second (abridged) ed.). International Commission on Stratigraphy. Archived from the original on 12 June 2020.
