Devonian Reef Complexes of the Canning Basin: 50 Years on

Playford, Phillip Elliott¹ (1) Geological Survey of Western Australia, Perth, Australia

The first detailed study of a Devonian reef complex in the Canning Basin was undertaken at the Oscar Range in 1956, followed by more detailed work at Windjana Gorge in 1958. Those two ground-breaking studies, by geologists of West Australian Petroleum (WAPET), laid the foundation for future research on these rocks.

Fundamental advances in understanding of the reefs over the past 50 years include recognition of:

• steep depositional dips in marginal-slope deposits; • facies equivalence of platform, marginal-slope, and basin deposits; • the major role of microbes in limestone deposition; • fracturing of early-cemented limestones leading to networks of neptunian dikes, platform-margin collapse, and major debris-flows; • large microbial bioherms which grew in water more than 100 meters deep; • well-defined cement stratigraphy; • precise biostratigraphic zonation using conodonts and ammonoids; • the role of contemporary tectonism and sea-level change in controlling development of the reef complexes; • the interrelationships between facies of the reef complexes and contemporaneous conglomerates; • growth of stromatolite mounds over cool-water seeps, with barite and iron-sulfide mineralization; • the role of the Permian glaciation in planing-off the reef complexes and forming subglacial karst and N-channels.

The magnificently exposed and intensively studied Canning Basin reef complexes serve as a model for interpreting other reefal deposits elsewhere in the world, some of which contain major oilfields. Although only small fields have been found to date in the Canning Basin, there is the potential for larger discoveries if 3D seismic can be used to define the older (Frasnian and Givetian) reefs.