Ceglar, Nathan1, Mark R. W. Reilly1, Tobias H. D. Payenberg1,
Simon C. Lang1
(1) University of Adelaide, South Australia, Australia
ABSTRACT: Cyclical Deepwater Sedimentation in a Ponded Mini-Basin, Donkey Bore Syncline, South Australia
Deepwater ponded mini-basins associated with salt diapirs are important exploration
targets, and therefore outcrop analogues may play a useful role in providing vital
statistics for reservoir geometry and connectivity. This study focuses on an outcrop
analogue in the Donkey Bore Syncline, Flinders Ranges, South Australia.
The Donkey Bore Syncline adjacent to the Wirrealpa Diapir hosts a cyclical 400 m thick succession of Cambrian thinly bedded sandy slope turbidites and tempestites overlying a 10 m thick amalgamated sandy debris flow. Over 50 discrete cycles with individual sandstone beds ranging in thickness from decimetre to multi-metre scale have been recognised. Measured sections combined with outcrop gamma logs and aerial photographs enable the cycles to be correlated for up to eight kilometres along an oblique dip section.
The metre scale cycles comprise stacked 20 to 30 cm thick, fine-grained sandstones with hummocky-like lamination and sharp bases, interbedded with siltstone. These are interpreted as tempestites. Other sandstones are more sheet-like and have sharp bases, are typically massive or laminated, with climbing ripples and soft sediment deformation. These are interpreted as turbidites. Variation in the thickness of the cycles and the individual sandstone beds are interpreted as the result of fluctuating sediment supply controlled by low-amplitude sea-level changes overprinted by episodic storms.
This outcrop analogue is of comparable scale to mini-basins in the Gulf of Mexico, and provides an empirical dataset for use in laterally extensive thinly bedded sandy deepwater plays within diapir-related mini-basins.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.