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Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Ju ...
strata of the
Colorado Plateau The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States The southwestern United State ...
area of southeastern
Utah Utah ( , ) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

Utah
demonstrate the principles of stratigraphy. Stratigraphy is a branch of
geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the processes by which th ...

geology
concerned with the study of
rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition and the way in w ...
layers (
strata (Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is ...
) and layering (stratification). It is primarily used in the study of
sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Earth's surface, followed by cementation. Sedimentation Sedimentation is the tendency for particle (ecology), parti ...

sedimentary
and layered
volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a Rock (geology), rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of Volcano, volcanic origin. Like all rock types, t ...

volcanic rock
s. Stratigraphy has two related subfields:
lithostratigraphy through Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic period million years ago (Year, Mya) to the beginning of the Cretaceous period app ...
(lithologic stratigraphy) and
biostratigraphy Biostratigraphy is the branch of stratigraphy through Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic period million years ago (Year, Mya ...
(biologic stratigraphy).


Historical development

Catholic priest
Nicholas Steno Nicolas Steno ( da, Niels Steensen; Latinized to ''Nicolaus Steno'' or ''Nicolaus Stenonius''; 1 January 1638 – 25 November 1686
established the theoretical basis for stratigraphy when he introduced the
law of superposition#REDIRECT Law of superposition 250px, Layer upon layer of rocks on north shore of Isfjord (Svalbard), Isfjord, Svalbard, Norway. Since there is no overturning, the rock at the bottom is older than the rock on the top by the Law of Superposition. ...

law of superposition
, the
principle of original horizontality The Principle of Original Horizontality states that layers of sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wi ...
and the
principle of lateral continuity 300px, The Permian through Jurassic strata of the Colorado Plateau">Jurassic.html" ;"title="Permian through Jurassic">Permian through Jurassic strata of the Colorado Plateau area of southeastern Utah that makes up much of the famous prominent rock ...
in a 1669 work on the fossilization of organic remains in layers of sediment. The first practical large-scale application of stratigraphy was by
William Smith
William Smith
in the 1790s and early 19th century. Known as the "Father of English geology", Smith recognized the significance of
strata (Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is ...
or rock layering and the importance of fossil markers for correlating strata; he created the first
geologic map A geologic map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults, folds, are shown with strike and dip St ...
of England. Other influential applications of stratigraphy in the early 19th century were by
Georges Cuvier Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist Natural history is a domain of inquiry involving organisms, including animals, fungus, fungi, and plants, in ...

Georges Cuvier
and
Alexandre Brongniart Alexandre Brongniart (5 February 17707 October 1847) was a French chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a person who conducts Scientific m ...

Alexandre Brongniart
, who studied the geology of the region around Paris. (
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is also bordered b ...
)


Lithostratigraphy

Chalk layers in Image:Geology_of_Cyprus-Chalk.jpg.html" ;"title="Cyprus">Image:Geology of Cyprus-Chalk.jpg">Chalk layers in Cyprus, showing sedimentary layering Variation in rock units, most obviously displayed as visible layering, is due to physical contrasts in rock type ( environments_of_deposition_(known_as_facies.html" ;"title="sedimentary depositional environment">environments of deposition (known as facies">sedimentary depositional environment">environments of deposition (known as facies change). These variations provide a lithostratigraphy or lithologic stratigraphy of the rock unit. Key concepts in stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries imply about their original depositional environment. The basic concept in stratigraphy, called the
law of superposition#REDIRECT Law of superposition 250px, Layer upon layer of rocks on north shore of Isfjord (Svalbard), Isfjord, Svalbard, Norway. Since there is no overturning, the rock at the bottom is older than the rock on the top by the Law of Superposition. ...

law of superposition
, states: in an undeformed stratigraphic sequence, the oldest strata occur at the base of the sequence. Chemostratigraphy studies the changes in the relative proportions of trace elements and isotopes within and between lithologic units. Carbon and oxygen isotope ratios vary with time, and researchers can use those to map subtle changes that occurred in the paleoenvironment. This has led to the specialized field of isotopic stratigraphy.
Cyclostratigraphy Milankovitch variations, solar forcing, and glacial cycles. Image by Robert A. Rohde, under the CC BY-SA 3.0 license. Cyclostratigraphy is a subdiscipline of stratigraphy that studies Astronomy, astronomically forced climate cycles within sedimenta ...
documents the often cyclic changes in the relative proportions of
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (20 ...

mineral
s (particularly
carbonates In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline min ...
), grain size, thickness of sediment layers (
varve 300px, Pleistocene age varves at Scarborough Bluffs, Toronto">Scarborough_Bluffs.html" ;"title="Pleistocene age varves at Scarborough Bluffs">Pleistocene age varves at Scarborough Bluffs, Toronto, Ontario, Canada. The thickest varves are more than ...
s) and fossil diversity with time, related to seasonal or longer term changes in
palaeoclimate Paleoclimatology (in American and British English spelling differences, British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of history of Earth, ...
s.


Biostratigraphy

Biostratigraphy or paleontologic stratigraphy is based on
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the a ...

fossil
evidence in the rock layers. Strata from widespread locations containing the same fossil fauna and flora are said to be correlatable in time. Biologic stratigraphy was based on William Smith's
principle of faunal succession The principle of faunal succession, also known as the law of faunal succession, is based on the observation that sedimentary rock strata contain fossil A fossil (from Classical Latin: , literally "obtained by digging") is any preserved r ...
, which predated, and was one of the first and most powerful lines of evidence for,
biological evolution Evolution is change in the heritable characteristics of biological population In biology, a population is a number of all the organisms of the same group or species In biology, a species is the basic unit of biological classific ...
. It provides strong evidence for the formation (
speciation Speciation is the evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes that are ...

speciation
) and
extinction Extinction is the termination of a kind of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by ...

extinction
of
species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...

species
. The
geologic time scale The geologic time scale (GTS) is a system of chronological datingChronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such object or event to be located in a previously establish ...

geologic time scale
was developed during the 19th century, based on the evidence of biologic stratigraphy and faunal succession. This timescale remained a relative scale until the development of
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the ...
, which was based on an absolute time framework, leading to the development of chronostratigraphy. One important development is the Vail curve, which attempts to define a global historical sea-level curve according to inferences from worldwide stratigraphic patterns. Stratigraphy is also commonly used to delineate the nature and extent of
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's a ...
-bearing reservoir rocks, seals, and traps of
petroleum geology Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration). Sediment ...
.


Chronostratigraphy

Chronostratigraphy is the branch of stratigraphy that places an absolute age, rather than a relative age on rock
strata (Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is ...
. The branch is concerned with deriving geochronological data for rock units, both directly and inferentially, so that a sequence of time-relative events that created the rocks formation can be derived. The ultimate aim of chronostratigraphy is to place dates on the sequence of deposition of all rocks within a geological region, and then to every region, and by extension to provide an entire geologic record of the Earth. A gap or missing strata in the geological record of an area is called a stratigraphic hiatus. This may be the result of a halt in the deposition of sediment. Alternatively, the gap may be due to removal by erosion, in which case it may be called a stratigraphic vacuity.Martinsen, O. J. ''et al.'' (1999) "Cenozoic development of the Norwegian margin 60–64N: sequences and sedimentary response to variable basin physiography and tectonic setting" pp. 293–304 ''In'' Fleet, A. J. and Boldy, S. A. R. (editors) (1999) ''Petroleum Geology of Northwest Europe'' Geological Society, London
page 295
It is called a ''hiatus'' because deposition was ''on hold'' for a period of time. A physical gap may represent both a period of non-deposition and a period of erosion. A geologic fault may cause the appearance of a hiatus.Chapman, Richard E. (1983) ''Petroleum Geology'' Elsevier Scientific, Amsterdam
p. 33


Magnetostratigraphy

MagnetostratigraphyMagnetostratigraphy is a geophysical correlation technique used to date sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Earth's surface, followed by cemen ...
is a chronostratigraphic technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout a section. The samples are analyzed to determine their detrital
remanent Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. Colloquially, when a magnet is "magnetized" it has remanence. The r ...
magnetism (DRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. For sedimentary rocks this is possible because, as they fall through the water column, very fine-grained magnetic minerals (< 17  μm) behave like tiny
compass A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...

compass
es, orienting themselves with
Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from structure of Earth, Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the S ...
. Upon burial, that orientation is preserved. For volcanic rocks, magnetic minerals, which form in the melt, orient themselves with the ambient magnetic field, and are fixed in place upon crystallization of the lava. Oriented paleomagnetic core samples are collected in the field;
mudstone Mudstone, a type of mudrock Mudrocks are a class of fine grained Sedimentary rock#Clastic sedimentary rocks, siliciclastic sedimentary rocks. The varying types of mudrocks include: ''siltstone'', ''claystone'', ''mudstone'', ''slate'', and ''shal ...

mudstone
s,
siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility (geology), fissility.Blatt ...
s, and very fine-grained
sandstone Sandstone is a clastic sedimentary rock of a clast (sand grain), derived from a basalt Basalt (, ) is a fine-grained extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ('' mafic '' ...

sandstone
s are the preferred lithologies because the magnetic grains are finer and more likely to orient with the ambient field during deposition. If the ancient magnetic field were oriented similar to today's field ( North Magnetic Pole near the North Rotational Pole), the strata would retain a normal polarity. If the data indicate that the North Magnetic Pole were near the South Rotational Pole, the strata would exhibit reversed polarity. Results of the individual samples are analyzed by removing the
natural remanent magnetizationNatural remanent magnetization (NRM) is the permanent magnetism of a Rock (geology), rock or sediment. This preserves a record of the Earth's magnetic field at the time the mineral was laid down as sediment or crystallized in magma and also the tecto ...
(NRM) to reveal the DRM. Following statistical analysis, the results are used to generate a local magnetostratigraphic column that can then be compared against the Global Magnetic Polarity Time Scale. This technique is used to date sequences that generally lack fossils or interbedded igneous rocks. The continuous nature of the sampling means that it is also a powerful technique for the estimation of sediment-accumulation rates.


See also

* Assise *
Bed (geology) upright=1, Tilted sedimentary bedding in shales of the Cretaceous Morro Solar Group">Salto del Fraile Formation, Peru. Beds are the layers of sedimentary rocks that are distinctly different from overlying and underlying subsequent beds of differe ...
* Conodont biostratigraphy * Erygmascope (old instrument for studying strata) *
Harris matrix The Harris matrix is a tool used to depict the temporal succession of archaeological context This page is a glossary of archaeology Archaeology or archeology is the study of human activity through the recovery and analysis of material cul ...
* Important publications in stratigraphy *
International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigrap ...
* Key bed * Sedimentary basin analysis *
Sequence stratigraphy Sequence stratigraphy is a branch of geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which ...
* Sadler effect *
TectonostratigraphyIn geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the processes b ...


References


Further reading

*Christopherson, R. W., 2008. ''Geosystems: An Introduction to Physical Geography'', 7th ed., New York: Pearson Prentice-Hall. *Montenari, M., 2016.
Stratigraphy and Timescales
', 1st ed., Amsterdam: Academic Press (Elsevier).


External links


University of South Carolina Sequence Stratigraphy WebInternational Commission on StratigraphyUniversity of Georgia (USA) Stratigraphy LabStratigraphy.net
A stratigraphic data provider.
Agenames.org
A global index of stratigraphic terms {{Authority control Petrology Methods in archaeology