Sedimentology, depositional environments and significance of an Ediacaran salt-withdrawal minibasin, Billy Springs Formation, Flinders Ranges, South Australia

Abstract

The late Ediacaran Billy Springs Formation is a little-studied, mudstone-dominated unit deposited in the Adelaide Rift Complex of South Australia. Sediments are exposed in an approximately 11 km x 15 km wide synclinal structure interpreted as a salt-withdrawal minibasin. The stratigraphic succession is characterized by convolute-laminated slump deposits, rhythmically-laminated silty mudstones, rare diamictites and fining-upward turbidite lithofacies. Lithofacies are the product of deposition in a deepwater slope or shelf setting, representing one of the few such examples preserved within the larger basin. Although exact correlations with other formations are unclear, the Billy Springs Formation probably represents the distal portion of a highstand systems tract, and is overlain by coarser sediments of the upper Pound Subgroup. Diamictite intervals are interpreted to be the product of mass flow processes originating from nearby emergent diapirs, in contrast to previous studies that suggest a glacial origin for extrabasinal clasts. Within the spectrum of outcropping minibasins around the world, the sediments described here are unique in their dominantly fine-grained nature and overall lithological homogeneity. Exposures such as these provide an opportunity to better understand the sedimentological processes that operate in these environments, and provide an analogue for similar settings in the subsurface that act as hydrocarbon reservoir-trap systems.