SEDIMENTARY GEOLOGY AND EVOLUTION OF AN OUTCROPPING SHELF-MARGIN DELTA, LATE PROTEROZOIC WONOKA FORMATION, SOUTH-AUSTRALIA

Discrete sand units or accumulations crop out within the late Proteroz oic Wonoka Formation, northern Flinders Ranges, South Australia. These sand wedges are unique in their size, contacts, facies, and associati ons to other sands in the formation and are interpreted as shelf margi n deltas. The wedges can be divided into a main body and a series of d iscrete feeder channels. The main body consists of basal slump masses, a sandstone-dominated succession, and an overlying shale-dominated fa cies. Lithofacies grossly define a deepening-upward succession from a lower shoreface to outer shelf setting. The formation and deposition o f the feeder channels and sand wedges was controlled largely by relati ve sea level changes. Initial exposure of the shelf and subaerial eros ion produced a regional erosional surface and incised valleys across t he paleoshelf. Prior to deposition of the wedges, slope instabilities and minor uplift occurred. Sediment was then transported across the sh elf and deposited near or at the shelf break and reworked in a shallow marine environment. Deposition of the shelf-margin deltas continued d uring relative sea level rise, but ended with shelf drowning.