MUD CRACKS

A polygonal network of downwardtapering cracks on a surface of cohesive sediment (mud) that may be preserved as a sedimentary structure in sedimentary deposits by an infilling of sand. Most are desiccation cracks (sun cracks), formed by shrinkage as the mud dried: they may be associated with evaporite minerals or pseudomorphs and are a valuable indicator of exposure in a palaeoenvironment. Cracks can also form in association with the expulsion of pore water in subaqueous settings: these synaeresis cracks are most commonly found in lacustrine deposits and can be confused with desiccation cracks.

[See alsofrost crack]