Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time. Stratigraphy, a branch of Geology, studies rock layers and layering ( stratification) In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of

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). Biostratigraphy is the branch of Stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the Fossil assemblages contained The aim of chronostratigraphy is to give a meaningful age date to these fossil assemblage intervals and interfaces. In the Natural sciences under the umbrella of Natural history, Geochronology is the Science of determining the absolute age of rocks, Fossils

Contents 1 Methodology 2 Units 3 Chronostratigraphy at a Glance 4 See also 5 References

Methodology

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. Isotope geochemistry is an aspect of Geology based upon study of the relative and absolute concentrations of the elements and their Isotopes in the In the Natural sciences under the umbrella of Natural history, Geochronology is the Science of determining the absolute age of rocks, Fossils However it is practically very difficult to isotopically date most fossils and sedimentary rocks directly, and thus inferences must be made in order to arrive at an age date which reflecs 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 assemblage which may be dated more accurately and precisely by isotopic methods, the construction of a chronostratigraphic column will rely heavily on intrusive and extrusive igneous rocks. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock

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 limits to the age at which a bed could be 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.

However, 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:^[1]

• eonothem - Phanerozoic
• erathem - Paleozoic
• system - Ordovician
• series - Upper Ordovician
• stage - Ashgill

Chronostratigraphy at a Glance

— Chronostratigraphic units refers to the rocks in quarries, drill cores, seismographic charts etc^[2]. The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed The Paleozoic or Palaeozoic Era (from the Greek palaio (παλαιο "old" and zoe (ζωη "life" meaning "ancient life" The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 A quarry is a type of open-pit mine from which rock or Minerals are extracted
— Rocks of the Upper Jurassic Series were formed during the Late Jurassic Epoch^[3]. The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning
— You can write: Tyrannosaurus rex was found in Upper Cretaceous, but if you write:"the T-rex was living in Upper Cretaceous", you mean that the T-rex was living inside the rock!

Chronostratigraphy is such an important branch of stratigraphy, because the age correlations derived are crucial to drawing accurate cross sections of the spatial organization of rocks and to prepare accurate paleogeographic reconstructions. Tyrannosaurus ( or, meaning 'tyrant lizard' is a Genus of Theropod Dinosaur. The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of

See also

• Stratigraphy
• Geologic time scale
• Geochronology
• Isotope geology
• Law of superposition
• Biostratigraphy
• Tectonostratigraphy

References

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