A review of allochthonous salt tectonics in the Flinders and Willouran ranges, South Australia

The Flinders and Willouran ranges of South Australia contain over 20 examples of exposed allochthonous salt sheets and canopies comprising the Callanna Group megabreccias. The identification of a given diapir or portion of a diapir as allochthonous is well documented in some cases but more speculative in others. Here we summarise most of the examples, citing the evidence and arguments supporting allochthonous origins and discussing relevant geometries and aspects of salt-sediment interaction. The allochthonous bodies are distributed over a large area, from the eastern Willouran Ranges to the Northern and Central Flinders Ranges, with fewer occurrences in the Southern Flinders Ranges. However, apparent base-salt flats are largely confined to four specific stratigraphic intervals that are in places linked by base-salt ramps. These levels are the Skillogalee Dolomite (Burra Group), the Tapley Hill Formation (Umberatana Group), and the Brachina and Bunyeroo formations (Wilpena Group), with ramps and minor flats continuing up through the Pound Subgroup and into Cambrian strata. At least three of the units with flats represent times of slow deposition, which favours lateral salt emplacement. Those in the Wilpena Group may also have been facilitated by minor contractional squeezing of feeder diapirs during early stages of the Delamerian Orogeny. The Flinders and Willouran ranges provide an exceptional natural laboratory for studies of outcropping structures analogous to those found in the subsurface of other salt basins such as the Gulf of Mexico and Atlantic margins. The diapirs and allochthonous salt sheets of the Flinders Ranges were also a key component of the basin framework in which strata containing Ediacaran fauna were deposited.