Peat diapirs 3-4 ft high are found in Recent sediments of the Flevoland, The Netherlands. The peat (Lower Peat) was deposited approximately 7,000 years ago on an eroded Pleistocene surface. The 4 to 6 ft of sediments which overlies the peat includes, from oldest to youngest, Unio Clay, Cardium Clay, Young Peat, and Almere and Zuiderzee deposits. Small-scale diapiric folds and related structures, similar to the larger Gulf Coast structures, are present in the Recent deposits on the flanks of several elongate Pleistocene sand ridges. The structures most like those of the Gulf Coast are down-to-the-basin normal faults, rim synclines, and, in one place, a central graben. The diapiric folds are found where the dip of the onlapping Recent sediments increases along the flanks of the sand ridges. The folds probably resulted from peat flowage down the ridge slopes. The time of diapirism can be dated as about 1,000 to 1,500 years B.P., inasmuch as the overlying Zuiderzee deposits (400 years B.P.) generally are not involved.
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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.