The theory ofbiorhexistasy describes climatic conditions necessary for periods ofsoil formation (pedogenesis) separated by periods ofsoil erosion. Proposed bypedologist Henry Erhart in 1951, the theory defines two climatic phases: biostasy and rhexistasy.[1]
During biostasy, abundant and regularprecipitation induces strong pedogenesis characterized by chemical alteration ofparent material and intensifiedeluviation andilluviation of soil minerals within thesurface soil andsubsoil layers (thesolum). These processes contribute to the formation of eluvial andargillichorizons and an increased concentration of iron oxides, aluminum oxides, and othersesquioxides in thesubsoil. Climatic conditions favor a vegetative cover which protects the soil from physical erosion but abundant rainfall results in the loss of mineral ions and increased concentration of those minerals in receiving bodies of water. Abundant marine calcium results inlimestone formation.
During rhexistasy (from rhexein, to break) the protective vegetative cover is reduced or eliminated as a result of a drier climate. Rainfall intensity is higher. The drier climate slows pedogenesis and soils no longer contribute the limestone building mineral components that characterize biostasy. Unprotected by thick vegetation or deep soils, wind acts to expose subsoil to erosion and rock to physicalweathering. Freeze-thaw acts to increase the production of coarse detrital materials. The intensity of punctuating rainfall events during rhexistasy results in erosion, and the accumulation ofsand andsilt assedimentary layers. During rhexistasy, the dominance of chemical weathering that characterizes biostasy is replaced by the dominance of physical weathering.
During thePleistocene epoch, the periods ofglaciation are considered to be periods of rhexistasy and theinterglacial are considered periods of biostasy.
The theory of biorhexistasy is used in various capacities: