Diapiric Structures and Late Precambrian-Early Cambrian Sedimentation in Flinders Ranges, South Australia1
C. R. Dalgarno, J. E. Johnson, 1968. "Diapiric Structures and Late Precambrian-Early Cambrian Sedimentation in Flinders Ranges, South Australia", Diapirism and Diapirs: a symposium, Jules Braunstein, Gerald D. O’Brien
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There are approximately 40 discrete diapiric structures in the Flinders Ranges of South Australia. The eroded cores of these structures, composed of incompetent dolomite-siltstone derived from the lower part of the Adelaide System (late Precambrian and Early Cambrian), range up to several miles in diameter. The carbonate-siltstone has been injected as a breccia and the injection has resulted in the formation of irregular bodies with dike-like tongues and complicated folds. The diapiric structures are along fairly well-defined trends which are regarded as the manifestation of a basement fault system.
Growth of the diapiric structures influenced later sedimentation. Bald-cap structures and inter-digitation of conglomerate with basin strata along the flanks of the domes indicate repeated phases of diapir movement. Adjacent diapirs show evidence of uplift at widely different times, from the glacial phase of the late Precambrian to the Early Cambrian. The bounding faults of a graben which developed above one diapir during the Early Cambrian controlled the development of an Archaeo-cyatha biohermal bank which intertongues with basinal facies. Several other diapirs are located along an important hinge line which controlled facies and thickness changes during Marinoan and Cambrian times.
Diapiric structures which affected late Precambrian and early Paleozoic deposition have been reported 750 mi northwest in the Amadeus basin of central Australia. Evaporitic deposits there are described from within the Bitter Springs Limestone, which is beneath an upper Precambrian glacial unit that is correlated with the Sturtian glacial deposits of the Adelaide System.
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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.