MINING GEOLOGY West Australiana

The Devonian reef complexes of the Canning Basin form a spectacular belt of rugged limestone ranges that extend for some 350 km along the northern margin of the basin. They have become known as the ‘Devonian Great Barrier Reef’ and constitute what is regarded as one of the world’s best examples of an ancient barrier-reef system.

Systematic research on these reefs began in 1956, when West Australian Petroleum Pty Ltd (WAPET) conducted detailed mapping and research of the Oscar Range reef complex, followed in 1958 by a study of Windjana Gorge. The reports on those investigations laid firm foundations for subsequent studies. The first mapping and research by the Geological Survey of Western Australia (GSWA) was undertaken in 1962 – 63, resulting in Bulletin 118, published in 1966. Field work for the present Bulletin was conducted during 1968, 1972, and several years since 1992. Many staff and students from Australian and overseas universities have worked with GSWA on the project. For its senior author this Bulletin represents the culmination of more than 50 years of his studies of these rocks.

The reefs were constructed during the Middle and Late Devonian by colonial organisms, mainly cyanobacteria, stromatoporoids, and corals. Those reef-building organisms are very well preserved, along with other fossils that once lived in and around the reefs, especially ammonoids, fish, and conodonts. Large masses of conglomerate, eroded from Precambrian rocks of the adjoining Devonian landmass, interfinger with or pass through the reef complexes.

The limestones have been faulted, tilted, and mildly folded in some areas, but are generally little deformed. During the Early Permian they were subjected to subglacial erosion and karstification below a succession of continental ice sheets. This subglacial erosion planed off the limestones forming a level surface that now approximates the tops of the ranges.

The Devonian reef complexes are highly prospective for zinc-lead deposits, and are also prospective for petroleum where they extend into the subsurface. Several zinc-lead deposits (including Pillara, Goongewa, and Cadjebut) and a small oilfield (Blina) have so far been discovered in these rocks.

• Geological ages
  Carboniferous, Cenozoic, Devonian, Permian
• Broad Terms
  Geomorphology, Geothermal energy, Mineralization, Petroleum, Petroleum geology, Regional geology, Stratigraphy, Structural geology
• Commodities
  Barite, Conglomerate, Limestone