Cryoturbation structures

Six types of cryoturbation structure (sedimentary deformations of cryogenic origin) can be distinguished and attributed to different mechanisms of formation and specific environmental conditions. Cryoturbations may result from (1) gravitational loading in thawing soil (‘periglacial loading’), (2) hydrostatic pressure between frozen parts of the subsoil (‘cryohydrostatic pressure’), or (3) ice-induced pressures due to differential frost penetration (‘cryostatic heave’). The first, and most common, process requires a reversed density gradient and conditions of liquefaction that are only possible during thaw of underlying frozen subsoil. The other two processes occur during freezing. Only large-amplitude deformations due to periglacial loading indicate the existence of permafrost, and therefore provide important paleoclimatic proxy indicators. All other cryoturbation types do not require permafrost conditions, but simply deep seasonal frost or repeated freeze-thaw cycles. Cryoturbations may enhance the storage of organic carbon in the soil and influence the global carbon cycle.