Abstract: Devonian reef complexes are spectacularly exposed in a series of limestone ranges along the northern margin of the Canning Basin in Western Australia and have become known as “The Devonian Great Barrier Reef.” The geological literature on these rocks dates back to 1884, and systematic research on them began during the late 1930s. Since then, many individuals and organizations have progressively increased knowledge of the stratigraphy and paleontology of the reef complexes, although one study concluded that they are products of “dynamic metamorphism.” Comprehensive research by the Geological Survey of Western Australia and its coworkers culminated in 2009 with the publication of a detailed account of the surface geology of the reef complexes and their associated terrigenous conglomerates. This article presents an overview of the research into the reef complexes, focusing on the key milestones and developments in knowledge and concepts.

Abstract The Devonian "Great Barrier Reef" of the Canning Basin developed beside a mountainous landmass of Precambrian rocks (the Kimberley Block) and around islands of Precambrian and Ordovician rocks. Basement topography, commonly fault controlled, was important in localizing the reefal platforms. Growth of the platforms was nearly continuous from late Givetian to late Famennian times, with only rare intervals of brief emergence. The earliest (Givetian) platforms were low-relief banks; later Frasnian and Famennian platforms were usually reef rimmed, with high relief. Upright reef margins predominated in the Frasnian, with intervals of backstepping in the late Frasnian associated with widespread drowning and the development of pinnacle reefs. A brief regression, with minor subaerial erosion of platforms (including mild karstification), occurred at the Frasnian-Famennian boundary, and the succeeding Famennian platforms advanced basinward over their equivalent marginal-slope and basin facies. Platform extinction in the late Famennian resulted from abrupt drowning. The hypothetical curve of relative sea level for the Canning Basin Devonian shows only partial resemblance to the Euramerican eustatic curve. In both areas, rapid rises in relative sea level in the late Frasnian caused widespread drowning of reefal platforms, followed by a brief regression at the Frasnian-Famennian boundary, which coincided with the world-wide mass extinction of metazoan reef builders. The Famennian regressions identified in Euramerica are not recognized in the Canning Basin, where the limestone platforms advanced continuously under conditions of steady rise or stillstand in relative sea level. Earthquakes associated with faulting during growth of the complexes resulted in extensive fracturing of rigid submarine-cemented limestones along the platform margins and upper marginal slopes, leading to the development of neptunian dikes and the collapse of platform margins to form massive debris flows. Contemporary faulting also influenced platform-basin morphology and was responsible for the mountainous topography of the adjoining landmass, which shed masses of boulder conglomerate and other terrigenous sediments interfingering with the reef complexes. Seismic stratigraphic modeling, in comparison with observed seismic records and well data, suggests that the evolutionary model for the Devonian reef complexes deduced from outcrop studies can also be recognized in the subsurface. Three small oil fields are associated with or overlie a well-defined subsurface Famennian platform margin. Recent research involving outcrop, core, seismic, and geochemical studies suggest, however, that the best prospects for future oil discoveries are likely to be in Givetian-Frasnian platforms, which have yet to be adequately tested. Mississippi Valley-type zinc-lead orebodies have been found in Givetian-Frasnian platforms in the outcrop area, and one of these is now being developed. The area is believed to have a good potential for further zinc-lead mining developments.