Diapiric Structures and Late Precambrian-Early Cambrian Sedimentation in Flinders Ranges, South Australia<xref ref-type="fn" rid="ch20fn1"><sup>1</sup></xref>

Abstract

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 Archaeocyatha 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.