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In
geology Geology (from the Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek ...

geology
and related fields, a stratum (plural: strata) is a layer of
sedimentary rock Sedimentary rocks are types 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 compoun ...

sedimentary rock
or
soil Soil is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

soil
, or
igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock i ...
that was formed at the Earth's surface, with internally consistent characteristics that distinguish it from other layers. The "stratum" is the fundamental unit in a stratigraphic column and forms the basis of the study of
stratigraphy Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks. Stratigrap ...

stratigraphy
. A stratum can be seen in almost every country in the world.


Characteristics

Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural processes. They may extend over hundreds of thousands of square kilometers of the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
's surface. Strata are typically seen as bands of different colored or differently structured material exposed in
cliff In geography and geology, a cliff is an area 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 ...

cliff
s,
road A road is a wide way leading from one place to another, typically one with a specially prepared surface which vehicles and bikes can use. Roads consist of one or two roadway A carriageway (British English British English (BrE) is the ...

road
cuts,
quarries A quarry is a type of open-pit mine File:Ende Gelände 2017 CHB 23 (cropped).jpg, The giant bucket-wheel excavators in the German Rhineland coal mines are among the world's biggest land vehicles. Open-pit mining, also known as open-cas ...

quarries
, and
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

river
banks. Individual bands may vary in thickness from a few
millimeter 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its deriveds scales. The Microwave are in-between 1 meter to 1 millimeter. The millimetre (American and British English spelling differences#-re, ...
s to a
kilometer The kilometre ( SI symbol: km; or ), spelt kilometer in American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to ...
or more. A band may represent a specific mode of
deposition Deposition may refer to: * Deposition (law), taking testimony outside of court * List of deposed politicians, Deposition (politics), the removal of a person of authority from political power * Deposition (university), a widespread initiation ritual ...
: river
silt Silt is granular material A granular material is a conglomeration of discrete solid, macroscopic scale, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when gra ...
, beach
sand Sand is a granular material composed of finely divided rock (geology), rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer ...

sand
, coal
swamp A swamp is a forested wetland A wetland is a distinct ecosystem that is flooded by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (Anoxic waters, anoxic) processes pre ...

swamp
,
sand dune A dune is a landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Land ...

sand dune
,
lava Lava is magma Magma () is the molten or semi-molten natural material from which all s are formed. Magma is found beneath the surface of the , and evidence of has also been discovered on other and some s. Besides molten rock, magma may al ...

lava
bed, etc.


Naming

Geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, although backgrounds in physics, chem ...

Geologist
s study rock strata and categorize them by the material of beds. Each distinct layer is typically assigned a name, usually based on a town, river, mountain, or region where the formation is exposed and available for study. For example, the
Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (Wuliuan, middle Cambrian), it is one of the earl ...
is a thick exposure of dark, occasionally
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

fossil
iferous,
shale Shale is a fine-grained, clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defi ...

shale
exposed high in the
Canadian Rockies The Canadian Rockies (french: Rocheuses canadiennes) or Canadian Rocky Mountains comprise both the Alberta's Rockies, Alberta Rockies and the B.C. Rockies in the Canada, Canadian segment of the North American Rocky Mountains. They are the easter ...

Canadian Rockies
near
Burgess Pass __NOTOC__ Burgess may refer to: People and fictional characters * Burgess (surname), a list of people and fictional characters * Burgess (given name), a list of people Places *Burgess, Missouri, United States *Burgess, South Carolina, United Stat ...
. Slight distinctions in material in a formation may be described as "members" (or sometimes "beds"). Formations are collected into "groups" while groups may be collected into "supergroups".


Gallery


See also

*
Archaeological horizon In archaeology Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. Archaeology is often considered a branch of socio-cultural anthropology, but archaeologists also draw from biolo ...
*
Geologic formation A geological formation, or formation, is a body of rock having a consistent set of physical characteristics (lithology as seen in southeastern Utah The lithology of a Rock (geology), rock unit is a description of its physical characteristics vis ...
*
Geologic map A geologic map or geological map is a special-purpose map A map is a symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by ...
*
Geologic unit A stratigraphic unit is a volume 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 compou ...
*
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
*
Bed (geology) upright=1, Tilted sedimentary bedding in Salto_del_Fraile_Formation,_Peru..html" ;"title="Cretaceous">shales of the Cretaceous Morro Solar Group">Salto del Fraile Formation, Peru.">Cretaceous">shales of the Cretaceous Morro Solar Group">Salto del ...


References


External links


GeoWhen Database
{{Authority control * Methods in archaeology