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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 compound, chemical composition and the way in w ...
that are formed by the accumulation or deposition 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. (2 ...

mineral
or
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or ...
particles at
Earth's surface Earth is the third planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to c ...

Earth's surface
, followed by cementation.
Sedimentation Sedimentation is the deposition of sediments Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring solid mass or aggreg ...
is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called
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 wind, water, or ice or by the force of gravity acting on the particles. ...

sediment
, and may be composed of
geological detritusDetritus (; adjective ''detrital'' ) is particles of Rock (geology), rock derived from pre-existing rock through processes of weathering and erosion.Essentials of Geology, 3rd Ed, Stephen Marshak, p G-7 A fragment of detritus is called a clast.Essent ...
(minerals) or
biological detritus
biological detritus
(organic matter). The geological detritus originated from
weathering Weathering is the deterioration of Rock (geology), rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little o ...
and
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or
mass movement A mass movement denotes a political party or movement which is supported by large segments of a population. Political movements that typically advocate the creation of a mass movement include the ideologies of communism Communism (from La ...
, which are called agents of
denudation , Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over ...
. Biological detritus was formed by bodies and parts (mainly shells) of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies (
marine snow In the deep ocean, marine snow is a continuous shower of mostly organic detritus In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical proces ...

marine snow
). Sedimentation may also occur as dissolved minerals precipitate from water solution. The sedimentary rock cover of the continents of the
Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere, a division of Earth's layers that includes the Crust (geology), ...
is extensive (73% of the Earth's current land surface), but sedimentary rock is estimated to be only 8% of the volume of the crust. Sedimentary rocks are only a thin veneer over a crust consisting mainly of
igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the p ...
and
metamorphic rock , a type of metamorphic rock Metamorphic rocks arise from the transformation of existing rock (geology), rock to new types of rock, in a process called metamorphism upright=1.35, Schematic representation of a metamorphic reaction. Abbreviat ...

metamorphic rock
s. Sedimentary rocks are deposited in layers as
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 a ...
, forming a structure called
bedding Bedding, also known as bedclothes or bed linen, is the materials laid above the mattress A mattress is a large, usually rectangular pad for supporting a lying A lie is an assertion that is believed to be false, typically used with the pur ...
. Sedimentary rocks are often deposited in large structures called
sedimentary basin Sedimentary basins are regions of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continent A continent is one of seve ...
s. Sedimentary rocks have also been found on
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carries the name of the Mars (mythology), Roman god of war and is often referred to ...

Mars
. The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for
civil engineering Civil engineering is a professional engineering Regulation and licensure in engineering is established by various jurisdictions of the world to encourage public welfare, safety, well-being and other interests of the general public and to defin ...
, for example in the construction of
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
s,
house A house is a single-unit residential building A building, or edifice, is a structure with a roof and walls standing more or less permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functio ...

house
s,
tunnel A tunnel is an underground passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A pipeline Pipeline may refer to: Electronics, computers and computing * Pipeline (comput ...

tunnel
s,
canal Canals are waterways channels Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * ...

canal
s or other structures. Sedimentary rocks are also important sources of
natural resource Natural resources are resource Resource refers to all the materials available in our environment which help us to satisfy our needs and wants. Resources can broadly be classified upon their availability — they are classified into renewabl ...
s including
coal Coal is a combustible , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , ...

coal
,
fossil fuel A fossil fuel is a hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structure ...
s,
drinking water Drinking water, also known as potable water, is water that is safe to drinking, drink or use for food preparation. The amount of drinking water required to maintain good health varies, and depends on physical activity level, age, health-related ...

drinking water
and
ore ore – psilomelane Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

ore
s. The study of the sequence of sedimentary rock strata is the main source for an understanding of the Earth's history, including
palaeogeography area during the Middle Devonian period. Image:Pangea animation 03.gif, upright=1.4, Animation of the break-up of the supercontinent Pangaea and the subsequent drift of its constituents, from the Early Triassic to recent (250 Ma to 0). Palaeoge ...
,
paleoclimatology Paleoclimatology (, palaeoclimatology) is the study of s for which direct measurements were not taken. As instrumental records only span a tiny part of , the reconstruction of ancient climate is important to understand natural variation and the e ...
and the
history of life The history of life on Earth traces the processes by which living and fossil organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Lif ...
. The
scientific discipline The branches of science, also referred to as science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Tes ...
that studies the properties and origin of sedimentary rocks is called
sedimentology Sedimentology encompasses the study of modern sediment Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring solid mass o ...
. Sedimentology is part of both
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
physical geography Physical geography (also known as physiography) is one of the two fields of geography Geography (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hell ...
and overlaps partly with other disciplines in the
Earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Ta ...
s, such as
pedology Pedology (from Greek: πέδον, ''pedon'', "soil"; and λόγος, ''logos'', "study") is a discipline within soil science Soil science is the study of soil Soil (often stylized as SOiL) is an American rock band that was formed in Chicago ...
,
geomorphology incised into shale at the foot of the North Caineville Plateau, Utah, within the pass carved by the Fremont River (Utah), Fremont River and known as the Blue Gate. Grove Karl Gilbert, GK Gilbert studied the landscapes of this area in great detail, ...

geomorphology
,
geochemistry Geochemistry is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanatio ...
and
structural geology Structural geology is the study of the three-dimensional distribution 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 th ...
.


Classification based on origin

Sedimentary rocks can be subdivided into four groups based on the processes responsible for their formation: clastic sedimentary rocks, biochemical (biogenic) sedimentary rocks, chemical sedimentary rocks, and a fourth category for "other" sedimentary rocks formed by impacts,
volcanism Volcanism (or volcanicity) is the phenomenon of eruption of molten rock (magma) onto the Earth#Surface, surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics and volcanic gases erupt through a break in the surface called ...
, and other minor processes.


Clastic sedimentary rocks

Clastic sedimentary rocks are composed of rock fragments (''clasts'') that have been cemented together. The clasts are commonly individual grains of
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...

quartz
,
feldspar Feldspars are a group of rock-forming aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity ...
,
clay minerals Clay minerals are hydrous aluminium Aluminium (aluminum in American English, American and Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than thos ...
, or
mica Micas ( ) are a group 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 natural ...

mica
. However, any type of mineral may be present. Clasts may also be ''lithic fragments'' composed of more than one mineral. Clastic sedimentary rocks are subdivided according to the dominant particle size. Most geologists use the
Udden-Wentworth
Udden-Wentworth
grain size scale and divide unconsolidated sediment into three fractions:
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifie ...

gravel
(>2 mm diameter),
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
(1/16 to 2 mm diameter), and
mud Mud is soil, loam, silt or clay mixed with water. It usually forms after rainfall or near water sources. Ancient mud deposits harden over geologic time scale, geological time to form sedimentary rock such as shale or mudstone (generally called l ...

mud
(<1/16 mm diameter). Mud is further divided into
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 ...
(1/16 to 1/256 mm diameter) and
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
(<1/256 mm diameter). The classification of clastic sedimentary rocks parallels this scheme; conglomerates and
breccia Breccia ( or ) is a rock composed of broken fragments of minerals In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid ...

breccia
s are made mostly of
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifie ...

gravel
,
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 made mostly of
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
, and
mudrock Mudrocks are a class of fine-grained Granularity (also called graininess), the condition of existing in granular material, granules or Grain, grains, refers to the extent to which a material or system is composed of distinction (philosophy), d ...
s are made mostly of mud. This tripartite subdivision is mirrored by the broad categories of
ruditeRudite is a general name used for a sedimentary rock composed of rounded or angular Detritus, detrital grains, i.e. Granule (geology), granules, pebbles, Cobble_(geology), cobbles, and boulders, which are coarser than sand in Particle size (grain siz ...
s,
arenite Arenite (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic ...
s, and
lutite Lutite is old terminology, which is not widely used, by Earth scientists in field descriptions for fine-grained, sedimentary rocks, which are composed of silt-size sediment Sediment is a naturally occurring material that is broken down by proce ...
s, respectively, in older literature. The subdivision of these three broad categories is based on differences in clast shape ( conglomerates and
breccia Breccia ( or ) is a rock composed of broken fragments of minerals In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid ...

breccia
s), composition (
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), or grain size or texture (
mudrock Mudrocks are a class of fine-grained Granularity (also called graininess), the condition of existing in granular material, granules or Grain, grains, refers to the extent to which a material or system is composed of distinction (philosophy), d ...
s).


Conglomerates and breccias

Conglomerates are dominantly composed of rounded
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifie ...

gravel
, while
breccia Breccia ( or ) is a rock composed of broken fragments of minerals In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid ...

breccia
s are composed of dominantly angular
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifie ...

gravel
.


Sandstones

Sandstone classification schemes vary widely, but most geologists have adopted the Dott scheme, which uses the relative abundance of quartz, feldspar, and lithic framework grains and the abundance of a muddy matrix between the larger grains. :''Composition of framework grains'' :The relative abundance of sand-sized framework grains determines the first word in a sandstone name. Naming depends on the dominance of the three most abundant components
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...

quartz
,
feldspar Feldspars are a group of rock-forming aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity ...
, or the lithic fragments that originated from other rocks. All other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. ::* Quartz sandstones have >90% quartz grains ::* Feldspathic sandstones have <90% quartz grains and more feldspar grains than lithic grains ::* Lithic sandstones have <90% quartz grains and more lithic grains than feldspar grains :''Abundance of muddy matrix material between sand grains'' ::When sand-sized particles are deposited, the space between the grains either remains open or is filled with mud (silt and/or clay sized particle). ::* "Clean" sandstones with open pore space (that may later be filled with matrix material) are called arenites. ::* Muddy sandstones with abundant (>10%) muddy matrix are called wackes. Six
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
names are possible using the descriptors for grain composition (quartz-, feldspathic-, and lithic-) and the amount of matrix (wacke or arenite). For example, a quartz arenite would be composed of mostly (>90%) quartz grains and have little or no clayey matrix between the grains, a lithic wacke would have abundant lithic grains and abundant muddy matrix, etc. Although the Dott classification scheme is widely used by sedimentologists, common names like
greywacke Photomicrograph of a lithic wacke (sandstone). Top image is in plane polarized light (PPL); bottom image is in cross polarized light (XPL). Blue epoxy fills pore spaces. Greywacke or graywacke ( German ''grauwacke'', signifying a grey, earthy r ...

greywacke
,
arkose Arkose () is a detritalDetritus (; adjective ''detrital'' ) is particles of rock derived from pre-existing rock through processes of weathering Weathering is the breaking down of rocks, soil Soil (often stylized as SOiL) is an American roc ...

arkose
, and quartz sandstone are still widely used by non-specialists and in popular literature.


Mudrocks

Mudrocks are sedimentary rocks composed of at least 50%
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 ...
- and
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
-sized particles. These relatively fine-grained particles are commonly transported by
turbulent flow In fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics (the study of air and other gases ...

turbulent flow
in water or air, and deposited as the flow calms and the particles settle out of
suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspende ...
. Most authors presently use the term "mudrock" to refer to all rocks composed dominantly of mud. Mudrocks can be divided into siltstones, composed dominantly of silt-sized particles; mudstones with subequal mixture of silt- and clay-sized particles; and claystones, composed mostly of clay-sized particles. Most authors use "
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
" as a term for a
fissile In nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, veh ...
mudrock (regardless of grain size) although some older literature uses the term "shale" as a synonym for mudrock.


Biochemical sedimentary rocks

Biochemical sedimentary rocks are created when organisms use materials dissolved in air or water to build their tissue. Examples include: * Most types of
limestone Limestone is a common type of carbonate 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 na ...

limestone
are formed from the calcareous skeletons of organisms such as
coral Corals are marine invertebrates Marine invertebrates are the invertebrates that live in marine habitats. Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a ver ...

coral
s,
mollusk Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number ...
s, and
foraminifera Foraminifera (; Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...
. *
Coal Coal is a combustible , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , ...

Coal
, formed from plants that have removed
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
from the atmosphere and combined it with other elements to build their tissue. * Deposits of
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a preci ...

chert
formed from the accumulation of siliceous skeletons of microscopic organisms such as
radiolaria The Radiolaria, also called Radiozoa, are protozoa Protozoa (also protozoan, plural protozoans) is an informal term for a group of single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microor ...

radiolaria
and
diatom Diatoms (''diá-tom-os'' 'cut in half', from ''diá'', 'through' or 'apart', and the root of ''tém-n-ō'', 'I cut') are a major group of algae Algae (; singular alga ) is an informal term for a large and diverse group of s. It is a grou ...

diatom
s.


Chemical sedimentary rocks

Chemical sedimentary rock forms when mineral constituents in
solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute and the water the solvent. In chemistry ...
become
supersaturated Supersaturation occurs with a chemical solution when the concentration of a solute exceeds the concentration specified by the value equilibrium solubility. Most commonly the term is applied to a solution of a solid in a liquid. A supersaturated sol ...
and inorganically
precipitate Precipitation is the process of conversion of a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All ever ...
. Common chemical sedimentary rocks include
oolitic limestone Oolite or oölite (''egg stone'') is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Ancient Greek word ''ᾠόν'' for egg (biology), egg. Strictly, oolites consist of ooids of d ...

oolitic limestone
and rocks composed of
evaporite An evaporite () is a water-soluble Solubility is the property of a solid, liquid or gaseous chemical substance called ''solution, solute'' to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depend ...
minerals, such as
halite Halite (), commonly known as rock salt, is a type of 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 crysta ...

halite
(rock salt),
sylvite Sylvite, or sylvine, is potassium chloride Potassium chloride (KCl, or potassium salt) is a metal halide Metal halides are compounds between metals and halogens. Some, such as sodium chloride are ionic, while others are covalently bonded. Cova ...

sylvite
,
baryte Baryte, barite or barytes (, ) is a 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 nat ...

baryte
and
gypsum Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

gypsum
.


Other sedimentary rocks

This fourth miscellaneous category includes volcanic
tuff Tuff is a type of Rock (geology), rock made of volcanic ash ejected from a Volcano, vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is consider ...

tuff
and
volcanic breccias
volcanic breccias
formed by deposition and later cementation of lava fragments erupted by volcanoes, and
impact breccias
impact breccias
formed after impact events. File:PIA17603 Erosion by Scarp Retreat in Gale Crater, Annotated Version.jpg, Sedimentary rocks on Mars, investigated by NASA's Curiosity Mars rover File:Chalus road - ninara 02.jpg, Steeply dipping sedimentary rock strata along the in northern Iran File:Entropy in Nature.jpg, Stratified remains of Puʻu Mahana cinder cone.


Classification based on composition

Alternatively, sedimentary rocks can be subdivided into compositional groups based on their mineralogy: * Siliciclastic sedimentary rocks, are dominantly composed of
silicate minerals Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide) is usually conside ...
. The sediment that makes up these rocks was transported as
bed load 300px, Bed load sediment in the Campbell Creek in Alaska">Campbell_Creek_(Alaska).html" ;"title="thalweg of Campbell Creek (Alaska)">Campbell Creek in Alaska. The term bed load or bedload describes particles in a flowing fluid (usually water) that ...
,
suspended load The suspended load of a flow of fluid, such as a 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 ...
, or by sediment gravity flows. Siliciclastic sedimentary rocks are subdivided into conglomerates and
breccia Breccia ( or ) is a rock composed of broken fragments of minerals In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid ...

breccia
s,
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
, and
mudrock Mudrocks are a class of fine-grained Granularity (also called graininess), the condition of existing in granular material, granules or Grain, grains, refers to the extent to which a material or system is composed of distinction (philosophy), d ...
s. * Carbonate rock, Carbonate sedimentary rocks are composed of calcite (rhombohedral ), aragonite (orthorhombic ), dolomite (), and other carbonate minerals based on the ion. Common examples include
limestone Limestone is a common type of carbonate 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 na ...

limestone
and the rock Dolomite (rock), dolomite. * Evaporite, Evaporite sedimentary rocks are composed of minerals formed from the evaporation of water. The most common evaporite minerals are carbonate minerals, carbonates (calcite and others based on ), Chlorine#Occurrence, chlorides (
halite Halite (), commonly known as rock salt, is a type of 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 crysta ...

halite
and others built on ), and sulfate mineral, sulfates (
gypsum Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

gypsum
and others built on ). Evaporite rocks commonly include abundant
halite Halite (), commonly known as rock salt, is a type of 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 crysta ...

halite
(rock salt),
gypsum Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

gypsum
, and anhydrite. * Organic-rich sedimentary rocks have significant amounts of organic material, generally in excess of 3% total organic carbon. Common examples include
coal Coal is a combustible , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , ...

coal
, oil shale as well as source rocks for oil and natural gas. * Siliceous rock, Siliceous sedimentary rocks are almost entirely composed of silica (), typically as
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a preci ...

chert
, opal, chalcedony or other microcrystalline forms. * Iron-rich sedimentary rocks are composed of >15% iron; the most common forms are banded iron formations and ironstones. * Phosphorite, Phosphatic sedimentary rocks are composed of phosphate minerals and contain more than 6.5% phosphorus; examples include deposits of phosphate nodules, bone beds, and phosphatic mudrocks.


Deposition and transformation


Sediment transport and deposition

Sedimentary rock (geology), rocks are formed when
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 wind, water, or ice or by the force of gravity acting on the particles. ...

sediment
is deposition (geology), deposited out of air, ice, wind, gravity, or water flows carrying the particles in
suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspende ...
. This sediment is often formed when
weathering Weathering is the deterioration of Rock (geology), rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little o ...
and
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
break down a rock into loose material in a source area. The material is then Sediment transport, transported from the source area to the deposition area. The type of sediment transported depends on the geology of the hinterland (the source area of the sediment). However, some sedimentary rocks, such as
evaporite An evaporite () is a water-soluble Solubility is the property of a solid, liquid or gaseous chemical substance called ''solution, solute'' to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depend ...
s, are composed of material that form at the place of deposition. The nature of a sedimentary rock, therefore, not only depends on the sediment supply, but also on the sedimentary depositional environment in which it formed.


Transformation (Diagenesis)

As sediments accumulate in a depositional environment, older sediments are buried by younger sediments, and they undergo diagenesis. Diagenesis includes all the chemical, physical, and biological changes, exclusive of surface weathering, undergone by a sediment after its initial deposition. This includes compaction (geology), compaction and lithification of the sediments. Early stages of diagenesis, described as ''eogenesis'', take place at shallow depths (a few tens of meters) and is characterized by bioturbation and mineralogical changes in the sediments, with only slight compaction. The red hematite that gives red beds, red bed sandstones their color is likely formed during eogenesis. Some biochemistry, biochemical processes, like the activity of bacteria, can affect minerals in a rock and are therefore seen as part of diagenesis. Deeper burial is accompanied by ''mesogenesis'', during which most of the compaction and lithification takes place. Compaction takes place as the sediments come under increasing overburden pressure, overburden (lithostatic) pressure from overlying sediments. Sediment grains move into more compact arrangements, grains of ductile minerals (such as
mica Micas ( ) are a group 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 natural ...

mica
) are deformed, and pore space is reduced. Sediments are typically saturated with groundwater or seawater when originally deposited, and as pore space is reduced, much of these connate fluids are expelled. In addition to this physical compaction, chemical compaction may take place via pressure solution. Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. The increased pressure and temperature stimulate further chemical reactions, such as the reactions by which organic material becomes lignite or
coal Coal is a combustible , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , ...

coal
. Lithification follows closely on compaction, as increased temperatures at depth hasten the precipitation (chemistry), precipitation of cement that binds the grains together. Pressure solution contributes to this process of cementation, as the mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. This further reduces porosity and makes the rock more compact and Competence (geology), competent. Unroofing of buried sedimentary rock is accompanied by ''telogenesis'', the third and final stage of diagenesis. As erosion reduces the depth of burial, renewed exposure to meteoric water produces additional changes to the sedimentary rock, such as Leaching (chemical science), leaching of some of the cement to produce secondary porosity. At sufficiently high temperature and pressure, the realm of diagenesis makes way for metamorphism, the process that forms
metamorphic rock , a type of metamorphic rock Metamorphic rocks arise from the transformation of existing rock (geology), rock to new types of rock, in a process called metamorphism upright=1.35, Schematic representation of a metamorphic reaction. Abbreviat ...

metamorphic rock
.


Properties


Color

The color of a sedimentary rock is often mostly determined by iron, an element with two major oxides: iron(II) oxide and iron(III) oxide. Iron(II) oxide (FeO) only forms under low oxygen (Anoxic waters, anoxic) circumstances and gives the rock a grey or greenish colour. Iron(III) oxide (Fe2O3) in a richer oxygen environment is often found in the form of the mineral hematite and gives the rock a reddish to brownish colour. In arid continental climates rocks are in direct contact with the atmosphere, and oxidation is an important process, giving the rock a red or orange colour. Thick sequences of red sedimentary rocks formed in arid climates are called red beds. However, a red colour does not necessarily mean the rock formed in a continental environment or arid climate. The presence of organic material can colour a rock black or grey. Organic material is formed from dead organisms, mostly plants. Normally, such material eventually decomposition, decays by oxidation or bacterial activity. Under anoxic circumstances, however, organic material cannot decay and leaves a dark sediment, rich in organic material. This can, for example, occur at the bottom of deep seas and lakes. There is little water mixing in such environments; as a result, oxygen from surface water is not brought down, and the deposited sediment is normally a fine dark clay. Dark rocks, rich in organic material, are therefore often
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
s.


Texture

The grain size, size, form and orientation of clasts (the original pieces of rock) in a sediment is called its texture (geology), texture. The texture is a small-scale property of a rock, but determines many of its large-scale properties, such as the density, porosity or Permeability (earth sciences), permeability. The 3D orientation of the clasts is called the fabric of the rock. The size and form of clasts can be used to determine the velocity and direction of current (stream), current in the sedimentary environment that moved the clasts from their origin; fine, calcareous mud only settles in quiet water while gravel and larger clasts are moved only by rapidly moving water. The grain size of a rock is usually expressed with the Wentworth scale, though alternative scales are sometimes used. The grain size can be expressed as a diameter or a volume, and is always an average value, since a rock is composed of clasts with different sizes. The Distribution (mathematics), statistical distribution of grain sizes is different for different rock types and is described in a property called the sorting (sediment), sorting of the rock. When all clasts are more or less of the same size, the rock is called 'well-sorted', and when there is a large spread in grain size, the rock is called 'poorly sorted'. The form of the clasts can reflect the origin of the rock. For example, coquina, a rock composed of clasts of broken shells, can only form in energetic water. The form of a clast can be described by using four parameters: * ''Surface texture'' describes the amount of small-scale relief of the surface of a grain that is too small to influence the general shape. For example, ''frosted grains'', which are covered with small-scale fractures, are characteristic of eolian sandstones. * ''Rounding (sediment), Rounding'' describes the general smoothness of the shape of a grain. * ''Sphericity'' describes the degree to which the grain approaches a sphere. * ''Grain form'' describes the three-dimensional shape of the grain. Chemical sedimentary rocks have a non-clastic texture, consisting entirely of crystals. To describe such a texture, only the average size of the crystals and the fabric are necessary.


Mineralogy

Most sedimentary rocks contain either
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...

quartz
(siliciclastic rocks) or calcite (carbonate rocks). In contrast to igneous and metamorphic rocks, a sedimentary rock usually contains very few different major minerals. However, the origin of the minerals in a sedimentary rock is often more complex than in an igneous rock. Minerals in a sedimentary rock may have been present in the original sediments or may formed by precipitation during diagenesis. In the second case, a mineral precipitate may have grown over an older generation of cement. A complex diagenetic history can be established by optical mineralogy, using a petrographic microscope. Carbonate rocks predominantly consist of carbonate minerals such as calcite, aragonite or Dolomite (mineral), dolomite. Both the cement and the clasts (including fossils and ooids) of a carbonate sedimentary rock usually consist of carbonate minerals. The mineralogy of a clastic rock is determined by the material supplied by the source area, the manner of its transport to the place of deposition and the stability of that particular mineral. The resistance of rock-forming minerals to weathering is expressed by the Goldich dissolution series. In this series, quartz is the most stable, followed by
feldspar Feldspars are a group of rock-forming aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity ...
,
mica Micas ( ) are a group 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 natural ...

mica
s, and finally other less stable minerals that are only present when little weathering has occurred. The amount of weathering depends mainly on the distance to the source area, the local climate and the time it took for the sediment to be transported to the point where it is deposited. In most sedimentary rocks, mica, feldspar and less stable minerals have been weathered to
clay minerals Clay minerals are hydrous aluminium Aluminium (aluminum in American English, American and Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than thos ...
like kaolinite, illite or smectite.


Fossils

Among the three major types of rock, fossils are most commonly found in sedimentary rock. Unlike most igneous and metamorphic rocks, sedimentary rocks form at temperatures and pressures that do not destroy fossil remnants. Often these fossils may only be visible under microscope, magnification. Dead organisms in nature are usually quickly removed by scavengers, bacteria, Decomposition, rotting and erosion, but under exceptional circumstances, these natural processes are unable to take place, leading to fossilisation. The chance of fossilisation is higher when the sedimentation rate is high (so that a carcass is quickly buried), in Hypoxia (environmental), anoxic environments (where little bacterial activity occurs) or when the organism had a particularly hard skeleton. Larger, well-preserved fossils are relatively rare. Fossils can be both the direct remains or imprints of organisms and their skeletons. Most commonly preserved are the harder parts of organisms such as bones, shells, and the woody tissue (biology), tissue of plants. Soft tissue has a much smaller chance of being fossilized, and the preservation of soft tissue of animals older than 40 million years is very rare. Imprints of organisms made while they were still alive are called trace fossils, examples of which are burrows, footprints, etc. As a part of a sedimentary rock, fossils undergo the same diagenesis, diagenetic processes as does the host rock. For example, a shell consisting of calcite can dissolve while a cement of silica then fills the cavity. In the same way, precipitating minerals can fill cavities formerly occupied by blood vessels, vascular tissue or other soft tissues. This preserves the form of the organism but changes the chemical composition, a process called permineralization. The most common minerals involved in permineralization are various forms of amorphous silica (chalcedony, flint,
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a preci ...

chert
), carbonates (especially calcite), and pyrite. At high pressure and temperature, the organic material of a dead organism undergoes chemical reactions in which Volatiles#Igneous petrology, volatiles such as water and carbon dioxide are expulsed. The fossil, in the end, consists of a thin layer of pure carbon or its mineralized form, graphite. This form of fossilisation is called carbonisation. It is particularly important for plant fossils. The same process is responsible for the formation of
fossil fuel A fossil fuel is a hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structure ...
s like lignite or
coal Coal is a combustible , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , ...

coal
.


Primary sedimentary structures

Structures in sedimentary rocks can be divided into ''primary'' structures (formed during deposition) and ''secondary'' structures (formed after deposition). Unlike textures, structures are always large-scale features that can easily be studied in the field. Sedimentary structures can indicate something about the sedimentary environment or can serve to tell way up structure, which side originally faced up where tectonics have tilted or overturned sedimentary layers. Sedimentary rocks are laid down in layers called Bed (geology), beds or Stratum, strata. A bed is defined as a layer of rock that has a uniform lithology and texture. Beds form by the deposition of layers of sediment on top of each other. The sequence of beds that characterizes sedimentary rocks is called
bedding Bedding, also known as bedclothes or bed linen, is the materials laid above the mattress A mattress is a large, usually rectangular pad for supporting a lying A lie is an assertion that is believed to be false, typically used with the pur ...
. Single beds can be a couple of centimetres to several meters thick. Finer, less pronounced layers are called laminae, and the structure a lamina forms in a rock is called lamination (geology), lamination. Laminae are usually less than a few centimetres thick. Though bedding and lamination are often originally horizontal in nature, this is not always the case. In some environments, beds are deposited at a (usually small) angle. Sometimes multiple sets of layers with different orientations exist in the same rock, a structure called cross-bedding. Cross-bedding is characteristic of deposition by a flowing medium (wind or water). The opposite of cross-bedding is parallel lamination, where all sedimentary layering is parallel. Differences in laminations are generally caused by cyclic changes in the sediment supply, caused, for example, by seasonal changes in rainfall, temperature or biochemical activity. Laminae that represent seasonal changes (similar to tree rings) are called varves. Any sedimentary rock composed of millimeter or finer scale layers can be named with the general term ''laminite''. When sedimentary rocks have no lamination at all, their structural character is called massive bedding. Graded bedding is a structure where beds with a smaller grain size occur on top of beds with larger grains. This structure forms when fast flowing water stops flowing. Larger, heavier clasts in suspension settle first, then smaller clasts. Although graded bedding can form in many different environments, it is a characteristic of turbidity currents. The surface of a particular bed, called the bedform, can also be indicative of a particular sedimentary environment. Examples of bed forms include dunes and ripple marks. Sole markings, such as tool marks and flute casts, are grooves eroded on a surface that are preserved by renewed sedimentation. These are often elongated structures and can be used to establish the direction of the flow during deposition. Ripple marks also form in flowing water. There can be symmetric or asymmetric. Asymmetric ripples form in environments where the current is in one direction, such as rivers. The longer flank of such ripples is on the upstream side of the current. Symmetric wave ripples occur in environments where currents reverse directions, such as tidal flats. Mudcracks are a bed form caused by the dehydration of sediment that occasionally comes above the water surface. Such structures are commonly found at tidal flats or point bars along rivers.


Secondary sedimentary structures

Secondary sedimentary structures are those which formed after deposition. Such structures form by chemical, physical and biological processes within the sediment. They can be indicators of circumstances after deposition. Some can be used as way up structure, way up criteria. Organic materials in a sediment can leave more traces than just fossils. Preserved tracks and burrows are examples of trace fossils (also called ichnofossils). Such traces are relatively rare. Most trace fossils are burrows of molluscs or arthropods. This burrowing is called bioturbation by sedimentologists. It can be a valuable indicator of the biological and ecological environment that existed after the sediment was deposited. On the other hand, the burrowing activity of organisms can destroy other (primary) structures in the sediment, making a reconstruction more difficult. Secondary structures can also form by diagenesis or the formation of a soil (pedogenesis) when a sediment is exposed above the water level. An example of a diagenetic structure common in carbonate rocks is a stylolite. Stylolites are irregular planes where material was dissolved into the pore fluids in the rock. This can result in the precipitation of a certain chemical species producing colouring and staining of the rock, or the formation of concretions. Concretions are roughly concentric bodies with a different composition from the host rock. Their formation can be the result of localized precipitation due to small differences in composition or porosity of the host rock, such as around fossils, inside burrows or around plant roots. In carbonate rocks such as
limestone Limestone is a common type of carbonate 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 na ...

limestone
or chalk,
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a preci ...

chert
or flint concretions are common, while terrestrial sandstones sometimes contain iron concretions. Calcite concretions in clay containing angular cavities or cracks are called septarian nodule, septarian concretions. After deposition, physical processes can Deformation (science), deform the sediment, producing a third class of secondary structures. Density contrasts between different sedimentary layers, such as between sand and clay, can result in flame structures or load casts, formed by inverted diapirism. While the clastic bed is still fluid, diapirism can cause a denser upper layer to sink into a lower layer. Sometimes, density contrasts occur or are enhanced when one of the lithologies dehydrates. Clay can be easily compressed as a result of dehydration, while sand retains the same volume and becomes relatively less dense. On the other hand, when the pore fluid pressure in a sand layer surpasses a critical point, the sand can break through overlying clay layers and flow through, forming discordant bodies of sedimentary rock called Clastic dike, sedimentary dykes. The same process can form mud volcanoes on the surface where they broke through upper layers. Sedimentary dykes can also be formed in a cold climate where the soil is permanently frozen during a large part of the year. Frost weathering can form cracks in the soil that fill with rubble from above. Such structures can be used as climate indicators as well as way up structures. Density contrasts can also cause small-scale fault (geology), faulting, even while sedimentation progresses (synchronous-sedimentary faulting). Such faulting can also occur when large masses of non-lithified sediment are deposited on a slope, such as at the front side of a River delta, delta or the continental slope. Instabilities in such sediments can result in the deposited material to slump (geology), slump, producing fissures and folding. The resulting structures in the rock are syn-sedimentary Fold (geology), folds and faults, which can be difficult to distinguish from folds and faults formed by tectonics, tectonic forces acting on lithified rocks.


Depositional environments

The setting in which a sedimentary rock forms is called the depositional environment. Every environment has a characteristic combination of geologic processes, and circumstances. The type of sediment that is deposited is not only dependent on the sediment that is transported to a place (Provenance (geology), provenance), but also on the environment itself. A Oceanic basin, marine environment means that the rock was formed in a sea or ocean. Often, a distinction is made between deep and shallow marine environments. Deep marine usually refers to environments more than 200 m below the water surface (including the abyssal plain). Shallow marine environments exist adjacent to coastlines and can extend to the boundaries of the continental shelf. The water movements in such environments have a generally higher energy than that in deep environments, as Wind wave, wave activity diminishes with depth. This means that coarser sediment particles can be transported and the deposited sediment can be coarser than in deeper environments. When the sediment is transported from the continent, an alternation of
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
,
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
and
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 ...
is deposited. When the continent is far away, the amount of such sediment deposited may be small, and biochemical processes dominate the type of rock that forms. Especially in warm climates, shallow marine environments far offshore mainly see deposition of carbonate rocks. The shallow, warm water is an ideal habitat for many small organisms that build carbonate skeletons. When these organisms die, their skeletons sink to the bottom, forming a thick layer of calcareous mud that may lithify into
limestone Limestone is a common type of carbonate 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 na ...

limestone
. Warm shallow marine environments also are ideal environments for coral reefs, where the sediment consists mainly of the calcareous skeletons of larger organisms. In deep marine environments, the water current working the sea bottom is small. Only fine particles can be transported to such places. Typically sediments depositing on the ocean floor are fine clay or small skeletons of micro-organisms. At 4 km depth, the solubility of carbonates increases dramatically (the depth zone where this happens is called the lysocline). Calcareous sediment that sinks below the lysocline dissolves; as a result, no limestone can be formed below this depth. Skeletons of micro-organisms formed of silica (such as radiolarians) are not as soluble and are still deposited. An example of a rock formed of silica skeletons is radiolarite. When the bottom of the sea has a small inclination, for example, at the continental slopes, the sedimentary cover can become unstable, causing turbidity currents. Turbidity currents are sudden disturbances of the normally quiet deep marine environment and can cause the near-instantaneous deposition of large amounts of sediment, such as sand and silt. The rock sequence formed by a turbidity current is called a turbidite. The coast is an environment dominated by wave action. At a beach, dominantly denser sediment such as sand or
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifie ...

gravel
, often mingled with shell fragments, is deposited, while the silt and clay sized material is kept in mechanical suspension. Tidal flats and shoals are places that sometimes dry because of the tide. They are often cross-cut by gully, gullies, where the current is strong and the grain size of the deposited sediment is larger. Where rivers enter the body of water, either on a sea or lake coast, River delta, deltas can form. These are large accumulations of sediment transported from the continent to places in front of the mouth of the river. Deltas are dominantly composed of clastic (rather than chemical) sediment. A continental sedimentary environment is an environment in the interior of a continent. Examples of continental environments are lagoons, lakes, swamps, floodplains and alluvial fans. In the quiet water of swamps, lakes and lagoons, fine sediment is deposited, mingled with organic material from dead plants and animals. In rivers, the energy of the water is much greater and can transport heavier clastic material. Besides transport by water, sediment can be transported by wind or glaciers. Sediment transported by wind is called aeolian processes, aeolian and is almost always sorting (sediment), very well sorted, while sediment transported by a glacier is called glacial till and is characterized by very poor sorting. Aeolian deposits can be quite striking. The depositional environment of the Touchet Formation, located in the Northwestern United States, had intervening periods of aridity which resulted in a series of rhythmite layers. Erosional cracks were later infilled with layers of soil material, especially from aeolian processes. The infilled sections formed vertical inclusions in the horizontally deposited layers, and thus provided evidence of the sequence of events during deposition of the forty-one layers of the formation.


Sedimentary facies

The kind of rock formed in a particular depositional environment is called its sedimentary facies. Sedimentary environments usually exist alongside each other in certain natural successions. A beach, where sand and gravel is deposited, is usually bounded by a deeper marine environment a little offshore, where finer sediments are deposited at the same time. Behind the beach, there can be dunes (where the dominant deposition is well sorted sand) or a lagoon (where fine clay and organic material is deposited). Every sedimentary environment has its own characteristic deposits. When sedimentary strata accumulate through time, the environment can shift, forming a change in facies in the subsurface at one location. On the other hand, when a rock layer with a certain age is followed laterally, the lithology (the type of rock) and facies eventually change. Facies can be distinguished in a number of ways: the most common are by the lithology (for example: limestone, siltstone or sandstone) or by fossil content. Coral, for example, only lives in warm and shallow marine environments and fossils of coral are thus typical for shallow marine facies. Facies determined by lithology are called Facies, lithofacies; facies determined by fossils are biofacies. Sedimentary environments can shift their geographical positions through time. Coastlines can shift in the direction of the sea when the sea level drops (Marine regression, regression), when the surface rises (transgression (geology), transgression) due to tectonic forces in the Earth's crust or when a river forms a large River delta, delta. In the subsurface, such geographic shifts of sedimentary environments of the past are recorded in shifts in sedimentary facies. This means that sedimentary facies can change either parallel or perpendicular to an imaginary layer of rock with a fixed age, a phenomenon described by Walther's Law. The situation in which coastlines move in the direction of the continent is called transgression (geology), transgression. In the case of transgression, deeper marine facies are deposited over shallower facies, a succession called onlap. Marine regression, Regression is the situation in which a coastline moves in the direction of the sea. With regression, shallower facies are deposited on top of deeper facies, a situation called offlap. The facies of all rocks of a certain age can be plotted on a map to give an overview of the
palaeogeography area during the Middle Devonian period. Image:Pangea animation 03.gif, upright=1.4, Animation of the break-up of the supercontinent Pangaea and the subsequent drift of its constituents, from the Early Triassic to recent (250 Ma to 0). Palaeoge ...
. A sequence of maps for different ages can give an insight in the development of the regional geography.


Gallery of sedimentary facies

File:Facies_migration2.jpg , A regressive facies shown on a stratigraphic column


Sedimentary basins

Places where large-scale sedimentation takes place are called
sedimentary basin Sedimentary basins are regions of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continent A continent is one of seve ...
s. The amount of sediment that can be deposited in a basin depends on the depth of the basin, the so-called ''Accommodation (geology), accommodation space''. The depth, shape and size of a basin depend on tectonics, movements within the Earth's lithosphere. Where the lithosphere moves upward (tectonic uplift), land eventually rises above sea level and the area becomes a source for new sediment as
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
removes material. Where the lithosphere moves downward (tectonic subsidence), a basin forms and sediments are deposited. A type of basin formed by the moving apart of two pieces of a continent is called a rift basin. Rift basins are elongated, narrow and deep basins. Due to divergent movement, the lithosphere is Deformation (mechanics), stretched and thinned, so that the hot asthenosphere rises and heats the overlying rift basin. Apart from continental sediments, rift basins normally also have part of their infill consisting of volcanic rock, volcanic deposits. When the basin grows due to continued stretching of the lithosphere, the rift grows and the sea can enter, forming marine deposits. When a piece of lithosphere that was heated and stretched cools again, its density rises, causing isostasy, isostatic subsidence. If this subsidence continues long enough, the basin is called a sag basin. Examples of sag basins are the regions along passive margin, passive continental margins, but sag basins can also be found in the interior of continents. In sag basins, the extra weight of the newly deposited sediments is enough to keep the subsidence going in a virtuous circle and vicious circle, vicious circle. The total thickness of the sedimentary infill in a sag basin can thus exceed 10 km. A third type of basin exists along convergent boundary, convergent plate boundaries – places where one tectonic plate moves under another into the asthenosphere. The subduction, subducting plate bends and forms a fore-arc basin in front of the overriding plate – an elongated, deep asymmetric basin. Fore-arc basins are filled with deep marine deposits and thick sequences of turbidites. Such infill is called flysch. When the convergent movement of the two plates results in continental collision, the basin becomes shallower and develops into a foreland basin. At the same time, tectonic uplift forms a mountain belt in the overriding plate, from which large amounts of material are eroded and transported to the basin. Such erosional material of a growing mountain chain is called molasse and has either a shallow marine or a continental facies. At the same time, the growing weight of the mountain belt can cause isostatic subsidence in the area of the overriding plate on the other side to the mountain belt. The basin type resulting from this subsidence is called a back-arc basin and is usually filled by shallow marine deposits and molasse.


Influence of astronomical cycles

In many cases facies changes and other lithological features in sequences of sedimentary rock have a cyclic nature. This cyclic nature was caused by cyclic changes in sediment supply and the sedimentary environment. Most of these cyclic changes are caused by astronomy, astronomic cycles. Short astronomic cycles can be the difference between the tides or the spring tide every two weeks. On a larger time-scale, cyclic changes in climate and sea level are caused by Milankovitch cycles: cyclic changes in the orientation and/or position of the Earth's rotational axis and orbit around the Sun. There are a number of Milankovitch cycles known, lasting between 10,000 and 200,000 years.For a short explanation of Milankovitch cycles, see ; . Relatively small changes in the orientation of the Earth's axis or length of the seasons can be a major influence on the Earth's climate. An example are the Quaternary glaciation, ice ages of the past 2.6 million years (the Quaternary Geologic time scale, period), which are assumed to have been caused by astronomic cycles. Climate change can influence the global sea level (and thus the amount of accommodation space in sedimentary basins) and sediment supply from a certain region. Eventually, small changes in astronomic parameters can cause large changes in sedimentary environment and sedimentation.


Sedimentation rates

The rate at which sediment is deposited differs depending on the location. A channel in a tidal flat can see the deposition of a few metres of sediment in one day, while on the deep ocean floor each year only a few millimetres of sediment accumulate. A distinction can be made between normal sedimentation and sedimentation caused by catastrophic processes. The latter category includes all kinds of sudden exceptional processes like Mass wasting, mass movements, rock slides or flooding. Catastrophic processes can see the sudden deposition of a large amount of sediment at once. In some sedimentary environments, most of the total column of sedimentary rock was formed by catastrophic processes, even though the environment is usually a quiet place. Other sedimentary environments are dominated by normal, ongoing sedimentation. In many cases, sedimentation occurs slowly. In a desert, for example, the wind deposits siliciclastic material (sand or silt) in some spots, or catastrophic flooding of a wadi may cause sudden deposits of large quantities of detrital material, but in most places eolian erosion dominates. The amount of sedimentary rock that forms is not only dependent on the amount of supplied material, but also on how well the material consolidates. Erosion removes most deposited sediment shortly after deposition.


Stratigraphy

That new rock layers are above older rock layers is stated in the Law of superposition, principle of superposition. There are usually some gaps in the sequence called unconformity, unconformities. These represent periods where no new sediments were laid down, or when earlier sedimentary layers were raised above sea level and eroded away. Sedimentary rocks contain important information about the history of the Earth. They contain fossils, the preserved remains of ancient plants and animals. Coal is considered a type of sedimentary rock. The composition of sediments provides us with clues as to the original rock. Differences between successive layers indicate changes to the environment over time. Sedimentary rocks can contain fossils because, unlike most igneous and metamorphic rocks, they form at temperatures and pressures that do not destroy fossil remains.


Provenance

Provenance (geology), Provenance is the reconstruction of the origin of sediments. All rock exposed at Earth's surface is subjected to physical or chemical
weathering Weathering is the deterioration of Rock (geology), rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little o ...
and broken down into finer grained sediment. All three types of rocks (
igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the p ...
, sedimentary and metamorphic rock, metamorphic rocks) can be the source of sedimentary detritus. The purpose of sedimentary provenance studies is to reconstruct and interpret the history of sediment from the initial parent rocks at a source area to final detritus at a burial place.


See also

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References


Notes


Bibliography

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External links


Basic Sedimentary Rock Classification
by Lynn S. Fichter, James Madison University, Harrisonburg.VI;

by Bruce Perry, Department of Geological Sciences, California State University at Long Beach . {{DEFAULTSORT:Sedimentary Rock Sedimentary rocks, Petrology Geology la:Sedimentum