Sedimentary structures include all kinds of features in

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

s and

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s, formed at the time of

deposition Deposition may refer to: * Deposition (law), taking testimony outside of court * Deposition (politics), the removal of a person of authority from political power * Deposition (university), a widespread initiation ritual for new students practiced f ...

. Sediments and sedimentary rocks are characterized by

bedding Bedding, also known as bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect. Bedding is the removable and washable portion of a human sleeping environm ...

, which occurs when layers of sediment, with different particle sizes are deposited on top of each other. These beds range from millimeters to centimeters thick and can even go to meters or multiple meters thick. Sedimentary structures such as

cross-bedding In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...

graded bedding In geology, a graded bed is one characterized by a systematic change in grain or clast size from one side of the bed to the other. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into pro ...

, and

ripple marks In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water ( current or waves) or wind. Defining ripple cross-laminae and asymmetric ripples * ''Current ripple marks'', ''u ...

are utilized in

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...

studies to indicate original position of

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

in geologically complex terrains and understand the

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...

of the sediment.

Flow structures

There are two kinds of flow structures: bidirectional (multiple directions, back-and-forth) and unidirectional. Flow regimes in single-direction (typically

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

) flow, which at varying speeds and velocities produce different structures, are called bedforms. In the ''lower flow regime'', the natural progression is from a flat bed, to some sediment movement ( saltation etc.), to ripples, to slightly larger dunes. Dunes have a vortex in the lee side of the dune. As the ''upper flow regime'' forms, the dunes become flattened out, and then produce

antidune An antidune is a bedform found in fluvial and other channeled environments. Antidunes occur in supercritical flow, meaning that the Froude number is greater than 1.0 or the flow velocity exceeds the wave velocity; this is also known as upper flo ...

s. At higher still velocity, the antidunes are flattened and most sedimentation stops, as erosion takes over as the dominant process.

Bedforms vs. flow

Typical unidirectional bedforms represent a specific flow velocity, assuming typical sediments (sands and silts) and water depths, and a chart such as below can be used for interpreting

s, with ''increasing'' water velocity going down the chart.

Ripple marks

Ripple marks usually form in conditions with flowing water, in the lower part of the Lower Flow Regime. There are two types of ripple marks: ; Symmetrical ripple marks: Often found on beaches, they are created by a two way current, for example the waves on a beach (swash and backwash). This creates ripple marks with pointed crests and rounded troughs, which aren't inclined more to a certain direction. Three common sedimentary structures that are created by these processes are herringbone cross-stratification, flaser bedding, and

interference ripples Interference Ripples are a type of sedimentary structure made up of two sets of ripples formed at right-angles to each other as a result of there being two dominant paleocurrents. These ripples may be formed in the beds of intermittent streams ...

. ; Asymmetrical ripple marks: These are created by a one way current, for example in a river, or the wind in a desert. This creates ripple marks with still pointed crests and rounded troughs, but which are inclined more strongly in the direction of the current. For this reason, they can be used as palaeocurrent indicators.

Antidunes

Antidunes are the sediment bedforms created by fast, shallow flows of water with a

Froude number In continuum mechanics, the Froude number (, after William Froude, ) is a dimensionless number defined as the ratio of the flow inertia to the external field (the latter in many applications simply due to gravity). The Froude number is based on ...

greater than 1. Antidunes form beneath standing waves of water that periodically steepen, migrate, and then break upstream. The antidune bedform is characterized by shallow

foresets A foreset bed is one of the main parts of a river delta. It is the inclined part of a delta that is found at the end of the stream channel as the delta sediment Sediment is a naturally occurring material that is broken down by processes of wea ...

, which dip upstream at an angle of about ten degrees that can be up to five meters in length.Boggs, Sam jr, 2006 Principles of Sedimentology and Stratigraphy, Patrick Lynch, Principles of Sedimentology and Stratigraphy, Pearson Prentice Hall, Upper Saddle River, NJ. Ed 4, p. 83-84 They can be identified by their low angle foresets. For the most part, antidunes bedforms are destroyed during decreased flow, and therefore cross bedding formed by antidunes will not be preserved.

Biological structures

A number of biologically-created sedimentary structures exist, called

trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

s. Examples include

burrow An Eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of s ...

s and various expressions of

bioturbation Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a ...

Ichnofacies An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited. Concept Trace fossil assemblages are far from random; the range of fossils recorded in association is constra ...

are groups of trace fossils that together help give information on the depositional environment. In general, as deeper (into the sediment) burrows become more common, the shallower the water. As (intricate) surface traces become more common, the water becomes deeper. Microbes may also interact with sediment to form

microbially induced sedimentary structure Microbially induced sedimentary structures (MISS) are primary sedimentary structures formed by the interaction of microbes with sediment and physical agents of erosion, deposition, and transportation. The structures commonly form when microbial ma ...

Soft sediment deformation structures

Soft-sediment deformation structures {{Short description, Geologic formation Soft-sediment deformation structures develop at deposition or shortly after, during the first stages of the sediment's consolidation. This is because the sediments need to be "liquid-like" or unsolidified ...

or SSD, is a consequence of the loading of wet sediment as burial continues after deposition. The heavier sediment "squeezes" the water out of the underlying sediment due to its own weight. There are three common variants of SSD: *load structures or

load casts Load casts are bulges, lumps, and lobes that can form on the bedding planes that separate the layers of sedimentary rocks. The lumps "hang down" from the upper layer into the lower layer, and typically form with fairly equal spacing. These feature ...

(also a type of sole marking) are blobs that form when a denser, wet sediment slumps down on and into a less dense sediment below. * pseudonodules or ball-and-pillow structures, are pinched-off load structures; these may also be formed by earthquake energy and referred to as seismites. *

flame structure A flame structure is a type of soft-sediment deformation that forms in unconsolidated sediments. The weight of an overlying bed forces an underlying bed to push up through the overlying bed, generally when both strata are saturated with water. ...

s, "fingers" of mud that protrude into overlying sediments. * clastic dikes are seams of sedimentary material that cut across sedimentary strata.

Bedding plane structures

Bedding Plane In geology, a bed is a layer of sediment, sedimentary rock, or pyroclastic material "bounded above and below by more or less well-defined bedding surfaces".Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds., 2005. ''Glossary of Geology'' ...

Structures are commonly used as

paleocurrent A paleocurrent or paleocurrent indicator is a geological feature (typically a sedimentary structure) that helps one determine the direction of flowing water in the geologic past. This is an invaluable tool in the reconstruction of ancient deposit ...

indicators. They are formed when sediment has been deposited and then reworked and reshaped. They include: * Sole markings form when an object gouges the surface of a sedimentary layer; this groove is later preserved as a cast when filled in by the layer above. They include: **Flute casts are scours dug into soft, fine sediment which typically get filled by an overlying bed. Measuring the long axis of the flute cast gives the direction of flow, with the scoop-shaped end pointing in the upcurrent direction and the tapered end pointing downcurrent (paleoflow direction). The convexity of the flute cast also points stratigraphically down. **Tool marks are a type of sole marking formed by grooves left in a bed by objects dragged along by a current. The average direction of these can be assumed to be the axis of flow direction. *

Mudcrack Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are sedimentary structures formed as muddy sediment dries and contracts.Jackson, J.A., 1997, ''Glossary of Geology'' (4th ed.), American Geological Institute, Alexandria, VA, ...

s form when mud is dewatered, shrinks, and leaves a crack. This tells you that the mud was saturated with water and then exposed to air. Mudcracks curl upwards, so they can be used as

geopetal A way up structure'', ''way up criterion, or geopetal indicator is a characteristic relationship observed in a sedimentary or volcanic rock, or sequence of rocks, that makes it possible to determine whether they are the right way up (i.e. in the at ...

structures.

Syneresis cracks Syneresis cracks (also known as subaqueous shrinkage cracks) are a sedimentary structure developed by the shrinkage of sediment without desiccation – not to be confused with desiccation cracks. Syneresis is the expulsion of a liquid from a ge ...

form in a similar way, with the exception that they are never exposed to air, instead being caused by changes in the salinity of the surrounding water. *

Raindrop impressions Raindrop impressions are a geological feature characterized by small crater-like pits with slightly raised edges that are the result of the impact of raindrop impacts on soft sediment surfaces. Sedimentary structures with similar appearance have ...

form on exposed sediment by raindrop impacts. * Parting lineations are subtly aligned minerals that form in the lower part of the Upper Flow Regime within plane beds. * Bomb sag or bedding-plane sag is downwards deformation of tuff beds or other deposits where a

volcanic bomb A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. Because volcanic bombs cool after they l ...

volcanic block A volcanic block is a fragment of rock that measures more than in diameter and is erupted in a solid condition. Blocks are formed from material from previous eruptions or from country rock and are therefore mostly accessory or accidental in or ...

has fallen.

Within bedding structures

These structures are within sedimentary bedding and can help with the interpretation of depositional environment and

directions. They are formed when the sediment is deposited. ;

Cross-bedding In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...

:Cross-bedding is the layering of beds deposited by wind or water inclined at an angle as much as 35° from the horizontal. Cross-beds form when sediment particles are deposited on steeper slopes of sand dunes on land or of sandbars in rivers and on the seafloor. Cross-bedding in wind-deposited dunes can be complex as a result of fast changing wind directions. ;

Hummocky cross-stratification Hummocky cross-stratification is a type of sedimentary structure found in sandstones. It is a form of cross-bedding usually formed by the action of large storms, such as hurricanes. It takes the form of a series of "smile"-like shapes, crosscu ...

: This stratification is made up of undulating sets of cross-laminae that are concave-up (swales) and convex-up (hummocks). These cross-beds gently cut into each other with curved erosional surfaces. They form in shallow-water, storm-dominated environments. Strong storm-wave action erodes the seabed into low hummocks and swales that lack a specific orientation. ; Imbrication: This structure is formed by the stacking of larger clasts in the direction of flow. ; Normal

: This structure occurs when current velocity changes and grains are progressively dropped out of the current. The most common place to find this is in a

turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites wer ...

deposit. This can also be inverted, called reversed graded bedding, and is common in

debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally ...

s. ;

Bioturbation Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a ...

: In many sedimentary rocks, the bedding is broken by cylindrical tubes a few centimeters in diameter that extend vertically through multiple beds. These sedimentary structures are remnants of burrows and tunnels excavated by marine organisms that live on the ocean floor. These organisms churn and burrow through mud and sand a process called bioturbation. They ingest the sediment, digest the organic matter, and leave behind the remnants which fills the burrow. ; Tidal bundle: Variation in bedding thickness in a tidal environment caused by alternation of spring and neap tides.

Secondary sedimentary structures

Secondary sedimentary structures form after primary deposition occurs or, in some cases, during the diagenesis of a

. Common secondary structures include any form of

, soft-sediment deformation,

teepee structure Teepee (also spelled tepee or tipi) structures are sedimentary structures interpreted to represent formation in peritidal environments. Teepees are largely the result of evaporation of water and subsequent precipitation of minerals within sedimen ...

s, root-traces, and soil mottling. Liesegang rings, cone-in-cone structures,

raindrop impressions Raindrop impressions are a geological feature characterized by small crater-like pits with slightly raised edges that are the result of the impact of raindrop impacts on soft sediment surfaces. Sedimentary structures with similar appearance have ...

, and vegetation-induced sedimentary structures would also be considered secondary structures. Secondary structures include fluid escape structures, formed when fluids escape from a sedimentary bed after deposition. Examples of fluid escape structures include dish structures, pillar structures, and vertical sheet structures.