Chronostratigraphy
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
Chronostratigraphy relies heavily upon
The methodology used is derived from the law of superposition and the principles of cross-cutting relationships.
Because
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
Chronostratigraphic units, with examples:[2]
- eonothem – Phanerozoic
- erathem – Paleozoic
- system – Ordovician
- series – Upper Ordovician
- stage – Ashgill
Differences from geochronology
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
- Biostratigraphy
- Chronozone
- Geochronology
- Geologic record
- Geologic time scale
- List of geochronologic names
- Tectonostratigraphy
References
- ^ Subcommission on Quaternary Stratigraphy (2002). "Chronostratigraphy". International Commission on Stratigraphy (ICS). Archived from the original on 28 July 2018.
- ISBN 978-0-922152-34-6.
- ISBN 978-0-442-28021-5.
- ISBN 978-0-521-44496-5.
- 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.