Drying cracking
Introduction
Soil desiccation is the process of forming polygonal cracks in compact soil as it loses water and humidity in periods of drought.
Clay-rich sediments are cohesive and individual particles tend to stick together as the sediment dries. As water is lost, the volume reduces and groups of clay minerals separate and develop cracks on the surface. In subaerial conditions, a polygonal pattern of cracks develops when the muddy sediment dries completely, this is called “desiccation marks or cracks”.[1].
Desiccation cracks mainly affect clay soils. The shrinkage of these soils can lead to the formation of cracks up to 4 cm wide and more than 1 m deep. The profound action of temperature changes and other atmospheric agents can then be the cause of subsequent landslides. They also play a role in the formation of polygonal soils and in crawling phenomena.
Desiccation marks occur in estuaries, lagoons, tidal flats, river floodplains, beach lakes, and other environments where muddy sediments are intermittently exposed and allowed to dry. They may be associated with raindrop or hail tracks, bubble and foam tracks, flat surface wavy marks, and vertebrate tracks (Plummer and Gostin, 1981). In modern sediments, desiccation marks are V-shaped fractures that taper downward and show a polygonal pattern. The area between the cracks is usually curved upwards in a concave shape, these mud cracks form in both siliciclastic muds and carbonate muds due to extreme desiccation (Nichols, 1999).
Paleoenvironmental importance
The paleoenvironmental importance of desiccation marks lies in their ability to provide valuable information about past environmental conditions. In ancient sedimentary rocks, desiccation marks are commonly preserved on top of bedding surfaces as positive relief fills of original cracks (Boggs, 2014). Here are some ways in which desiccation cracks are important from a paleoenvironmental perspective:.
Climate Indicators: Cracks can be sensitive indicators of changes in climate. For example, presence in sedimentary deposits may suggest periods of prolonged drought or arid conditions in the past. The distribution and size of desiccation cracks can also provide information on the intensity and duration of dry periods. (Cevallos-Ferriz, S. R. S., & Reiners, P. W, 1984).
Past hydrological regimes: The formation of desiccation cracks is closely related to changes in water content in soil or sediments. Therefore, their presence may indicate fluctuations in past hydrological regimes, such as flood episodes followed by periods of drought. (Middleton, G. V, 1967).