Mudcrack

Mudcracks (also known as desiccation cracks or mud cracks) are sedimentary structures formed as muddy sediment dries and contracts. Crack formation also occurs in clayey soils as a result of a reduction in water content.

Naturally forming mudcracks start as wet, muddy sediment desiccates, causing contraction. A strain is developed because the top layer tries to shrink while the material below stays the same size. When this strain becomes large enough, channel cracks form in the desiccated surface material, relieving the strain. Individual cracks spread and join up forming a polygonal, interconnected network. These cracks may later be filled with sediment and form casts on the base of the overlying bed.

Syneresis cracks are broadly similar features that form from subaqueous shrinkage of muddy sediment caused by differences in salinity or chemical conditions, rather than subaerial exposure and desiccation. Syneresis cracks can be distinguished from mudcracks because they tend to be discontinuous, sinuous, and trilete or spindle-shaped.

Mudcracks are generally polygonal in plan view 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 mud cracks based on their completeness, orientation, shape, and type of infill.

Complete mudcracks form an interconnected 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.

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.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.

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