![Dried mud creeks on the shores of the Wash - geograph](https://upload.wikimedia.org/wikipedia/commons/7/75/Dried_mud_creeks_on_the_shores_of_the_Wash_-_geograph.org.uk_-_10669.jpg)
Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are
sedimentary structures
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition.
Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different partic ...
formed as muddy sediment
dries and contracts.
[Jackson, J.A., 1997, ''Glossary of Geology'' (4th ed.), American Geological Institute, Alexandria, VA, 769 p.][Stow, D.A., 2005, ''Sedimentary Rocks in the Field'', Academic Press, London, 320 p.] Crack formation also occurs in clay-bearing soils as a result of a reduction in water content.
Formation of mudcrack
![Soil cracks00](https://upload.wikimedia.org/wikipedia/commons/0/03/Soil_cracks00.jpg)
Naturally forming mudcracks start as wet, muddy sediment
dries up and contracts. A strain is developed because the top layer shrinks while the material below stays the same size. When this strain becomes large enough, channel cracks form in the dried-up surface to relieve the strain. Individual cracks spread and join up, forming a polygonal, interconnected network of forms called "tesselations." If the strain continues to build the polygon start to curled upward. This characteristic can be used in geology to understand the original orientation of a rock. Cracks may later be filled with sediment and form
casts over the base.
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 ...
are broadly similar features that form from underwater shrinkage of muddy sediment caused by differences in salinity or chemical conditions,
rather than aerial exposure and desiccation. Syneresis cracks can be distinguished from mudcracks because they tend to be discontinuous,
sinuous
Sinuosity, sinuosity index, or sinuosity coefficient of a continuously differentiable curve having at least one inflection point is the ratio of the curvilinear length (along the curve) and the Euclidean distance (straight line) between the ...
, and trilete or spindle-shaped.
[Allen, J.R.L., 1982, ''Sedimentary Structures: Their Character and Physical Basis'' (v. 2): Elsevier, Oxford, 593 p.]
Morphology and classification of mudcrack
Mudcracks are generally polygonal when seen from above and v-shaped in cross section. The "v" opens towards the top of the bed and the crack tapers downward. Allen (1982) proposed a classification scheme for mudcracks based on their completeness, orientation, shape, and type of infill.
Completeness of mudcrack
''Complete mudcracks'' form an interconnected
tessellating
A tessellation or tiling is the covering of a surface, often a plane, using one or more geometric shapes, called ''tiles'', with no overlaps and no gaps. In mathematics, tessellation can be generalized to higher dimensions and a variety of ge ...
network. The connection of cracks often occurs when individual cracks join together forming a larger continuous crack.
''Incomplete mudcracks'' are not connected to each other but still form in the same region or location as the other cracks.
Plan-view geometry
''Orthogonal'' intersections can have a preferred orientation or may be random. In oriented orthogonal cracks, the cracks are usually complete and bond to one another forming irregular polygonal shapes and often rows of irregular polygons. In random orthogonal cracks, the cracks are incomplete and unoriented therefore they do not connect or make any general shapes. Although they do not make general shapes they are not perfectly geometric.
[Linholm, R., 1987, ''A Practical Approach to Sedimentology'', Allen and Unwin, London, 276 p.]
''Non-orthogonal'' mudcracks have a geometric pattern. In uncompleted non-orthogonal cracks they form as a single three-point star shape that is composed of three cracks. They could also form with more than three cracks but three cracks in commonly considered the minimum. In completed non-orthogonal cracks, they form a very geometric pattern. The pattern resembles small polygonal shaped tiles in a repetitive pattern.
Mud curls
Mud curls form during one of the final stages in
desiccation
Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container.
...
. Mud curls commonly occur on the exposed top layer of very thinly bedded mud rocks. When mud curls form, the water that is inside the sediment begins to evaporate causing the
stratified
Stratification may refer to:
Mathematics
* Stratification (mathematics), any consistent assignment of numbers to predicate symbols
* Data stratification in statistics
Earth sciences
* Stable and unstable stratification
* Stratification, or st ...
layers to separate. The individual top layer is much weaker than multiple layers and is therefore able to contract and form curls as desiccation occurs.
If transported by later currents, mud curls may be preserved as mud-chip rip-up clasts.
Environments and substrates
Naturally occurring mudcracks form in sediment that was once saturated with water. Abandoned river channels,
floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
muds, and dried ponds are localities that form mudcracks.
Mudcracks can also be indicative of a predominately sunny or shady environment of formation. Rapid drying, which occurs in sunny environments, results in widely spaced, irregular mudcracks, while closer spaced, more regular mudcracks indicate that they were formed in a shady place.
Similar features also occur in frozen ground,
lava flow
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...
s (as
columnar basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...
), and igneous
dykes and
sills.
In technology
Polygonal crack networks similar to mudcracks can form in man-made materials such as
ceramic glazes
Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a pottery body through firing. Glaze can serve to color, decorate or waterproof an item. Glazing renders earthenware vessels suitable for holdin ...
, paint film, and poorly made concrete. Mudcrack patterning at smaller scales can also be observed studied using technological
thin film
A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ap ...
s deposited using
micro
Micro may refer to:
Measurement
* micro- (μ), a metric prefix denoting a factor of 10−6
Places
* Micro, North Carolina, town in U.S.
People
* DJ Micro, (born Michael Marsicano) an American trance DJ and producer
*Chii Tomiya (都宮 ちい ...
and
nanotechnologies
Nanotechnology, also shortened to nanotech, is the use of matter on an atomic, molecular, and Supramolecular complex, supramolecular scale for industrial purposes. The earliest, widespread description of nanotechnology referred to the particul ...
.
[R. Seghir and S. Arscott "Controlled mud-crack patterning and self-organized cracking of polydimethylsiloxane elastomer surfaces" Sci. Rep. (Nature) 5, 14787 (2015). .]
Preservation of mudcrack
![Inverness mudcrack](https://upload.wikimedia.org/wikipedia/commons/9/93/Inverness_mudcrack.jpg)
Mudcracks can be preserved as v-shaped cracks on the top of a bed of muddy sediment or as casts on the base of the overlying bed. When they are preserved on the top of a bed, the cracks look as they did at the time of formation. When they are preserved on the bottom of the bedrock, the cracks are filled in with younger, overlying sediment. In most bottom-of-bed examples, the cracks are the part that sticks out most. Bottom-of-bed preservation occurs when mudcracks that have already formed and are completely dried are covered with fresh, wet sediment and are buried. Through burial and pressure, the new wet sediment is further pushed into the cracks, where it dries and hardens. The mudcracked rock is then later exposed to
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
.
In these cases, the original mud cracks will erode faster than the newer material that fills the spaces. This type of mudcrack is used by geologists to determine the vertical orientation of rock samples that have been altered through
fold
Fold, folding or foldable may refer to:
Arts, entertainment, and media
* ''Fold'' (album), the debut release by Australian rock band Epicure
*Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot
*Above ...
ing or
faulting
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
.
Gallery
Image:mudcracks_roundtop_hill_MD.jpg, Bedding plane view of ancient mudcracks
File:Mudcracks mcr3.jpg, Cross-sectional view of ancient mudcrack
File:Carmel Formation mudcracks Jurassic.jpg, Mudcracks in the Carmel Formation
The Carmel Formation is a geologic formation in the San Rafael Group that is spread across the U.S. states of Wyoming, Utah, Colorado, north east Arizona and New Mexico. Part of the Colorado Plateau, this formation was laid down in the Middle J ...
(Middle Jurassic) near Gunlock, Utah.
See also
*
Ground fissure
A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes.
Ground fissure
A ...
*
Syneresis crack
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 g ...
, which occur in muds and can look very similar, without requiring subaerial exposure
*
Craquelure
Craquelure (french: craquelé; it, crettatura) is a fine pattern of dense cracking formed on the surface of materials. It can be a result of drying, aging, intentional patterning, or a combination of all three. The term is most often used to ref ...
, a similar phenomenon in paintings and ceramics
References
External links
* {{Commons category-inline, Mudcracks
NEFI: A software that can be used to extract networks from images of mudcracks.
Sedimentary structures
Patterned grounds
Desiccation