In northern Germany there are more than 200 known salt stocks which are composed of Zech-stein salt. Because of favorable geologic conditions, it was possible to reconstruct the historical development of the salt stocks with the aid of reflection-seismic surveys. The development of a single salt stock appears to have started with an accumulation of salt, the so-called “salt pillow.” At a later stage, the overlying strata broke, allowing the diapir to form. In northern Germany, genetic connections between salt stocks are recognizable. Some of the larger groups of salt stocks are classified as “salt-stock families.” Such salt-stock families consist of several salt stocks grouped around the genetically oldest, which is said to be the “mother salt stock.” The rim synclines of the adjacent salt stocks become younger away from the center.
The geologic impulse causing the formation of mother salt stocks is supposedly partly tectonic, whereas the subsequent wave-front-like growth of the salt-stock families took place in a purely halo-kinetic way, that is, by the movement of salt under the influence of gravity. The absolute rate of the horizontal wave-front-like flow of the salt over great distances averages about 0.3 mm a year.
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“Diapir” and “diapirism” come from the Greek diapeirein, which means “to pierce.” Diapirism sensu lato is a process by which earth materials from deeper levels have pierced, or appear to have pierced, shallower materials; it is divided into magmatic intrusion and diapirism sensu stricto on the basis of the temperature at which piercement occurs. Diapirs s.s. are composed of evaporites, argillaceous sediments, coal, peat, ice, serpentine, or other earth materials which have the critical characteristics of low equivalent viscosity and low density. These materials range in age from Precambrian to Recent. Diapirs are found in all parts of the world except the shield areas. They have many forms, ranging from smoothly rounded pillows to complexly injected laminae, are either connected with or disconnected from the “mother” bed, and are present either at the surface, where they form distinctive features, or at considerable depth. Diapirs have well-developed internal structures indicative of an origin by flow. Strata around a diapir may be strongly affected structurally and/or stratigraphically by the diapir, or they may be unaffected. Field and model studies indicate that diapirs have developed as a result of horizontal compression, gravitational instability, or both. Diapiric structures of various types contain large quantities of oil and gas, sulfur, salt, and potash and are important for underground storage and nuclear testing.