Abstract Christmas tree diapirs in the Adelaide “Geosyncline” of South Australia are characterized by lateral tongues of allochthonous breccia derived from an autochthonous level that contains evaporites and a caprock assemblage of blocks (or ‘rafts’) of non-evaporitic lithologies. These breccias may be attached to a diapiric trunk (consisting of evaporites and breccias) that may be connected to the autochthonous level. This paper describes two prime examples that outcrop at Pinda Springs and Wirrealpa Springs in the central Flinders Ranges of South Australia. The Christmas tree diapirs evolved from an initially reactive triangular, or anvil-shaped, diapir and separate two mini-basins of different accommodation potential and often completely different sedimentary facies. An interpreted submarine salt glacier at Pinda diapir was extruded as an allochthonous salt tongue nearly 7 km long and 500 m thick. It overlies a major disconformity close to the diapir and the step-like base suggests aggradation and progradation within the transgressive systems tract. At Wirrealpa diapir, multiple tongues are contained within some 50 high-frequency sequences of the main mini-basin where deposition was influenced by the high subsidence rate, coupled with high sediment supply. The distinction is made between halokinetic sequences bounded by ravinement surfaces and the high-frequency sequences bounded by regressive surfaces of erosion. Both sequence types can be arranged into progradational, aggradational, and retrogradational stacking patterns. The model for Christmas tree diapirs, based on outcrop mapping, done as part of this study, suggests that a number of potential hydrocarbon traps can be related to different stages in the evolution of these halokinetic structures.

Abstract Salt-sediment interaction influence the stratigraphic architecture of depositional sequences during the passive margin stage of development of the Adelaide Geosyncline in South Australia. This late Precambrian to Early Cambrian succession outcrops in the Flinders ranges and is punctuated by submarine unconformities. The unconformities are interpreted as deep-water sequence boundaries that have no shallow water equivalent. However, they can be traced laterally into condensed sections or major flooding surfaces. These sequence boundaries are typically overlain by deep-water facies that reflect the high rate of subsidence coupled with high sedimentation rates typically found in halotectonic mini-basins. Large-scale slumping and canyon incision often mark the deep-water sequence boundaries. Canyon incision is associated with salt withdrawal or downbuilding in mini-basins. The architecture of submarine canyons is defined by the nature and correlation of bounding surfaces, sandstone interconnectivity and lithofacies elements. These features are often beyond the limits of seismic resolution in basins where passive margin development was influenced by salt tectonics.