Compartmentalization of Deepwater Sediments in a Mini-Basin Fill: An Outcrop Example from the Donkey Bore Syncline, Flinders Ranges, South Australia

Blaise Fernandes, Carmen Krapf, Kerrie E. Deller, Simon C. Lang, and Tobias H.D. Payenberg
University of Adelaide, Adelaide, Australia

The Cambrian Donkey Bore Syncline, Flinders Ranges, South Australia, is a rare example of outcropping deepwater sediments in a salt-withdrawal mini-basin. It is situated adjacent to the Wirrealpa Diapir and contains 400m of vertical basin fill exposed in an area of approximately 20 km2. Its triangular shape, shallow-dipping beds and arid climate enable the vertical and horizontal mapping of individual sandbodies in a 3D exposure. The Wirrealpa Diapir is located at the southeastern end of the syncline. There, effects of diapiric movements are represented in form of slumps and mass wasting in the sediments.

High-resolution vertical sections along the southern and southeastern side of the syncline were measured. Individual beds compounded in coarsening-upwards lobes comprise dominantly of densites and debrites. Bed thicknesses range between a few centimeters to 2 metres through internal slumping. Individual lobes are 20 to 50 metres thick, and comprise sand-, silt- and mudstones. The sandy lobes are laterally extensive, and their limits can be mapped by walking out individual beds between the sections. Within the lobes the typical lengths of individual sandstone beds are between 2 and 4 kilometres, giving width to thickness ratios of around 2000:1.

Although laterally quite extensive, the finite length of the sandstone bodies provides a relatively high level of compartmentalization. Interestingly, individual lobes are subtly offset from one another, even if they appear continuous on a larger scale. Such subtle lobe compartmentalization might be important for better predicting flow units in subsurface salt-related deepwater plays.