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Lindsay Collins, Curtin University (Australia)
Andrew Shuckstes, WorleyParsons (Australia)
Michael Page, WorleyParsons (Australia)
Viviane Testa, Curtin University (Australia)
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The North West Shelf is a modern tropical ramp which is underlain by Cretaceous-Tertiary limestones. Coral reef systems, discontinuously developed, vary from fringing reefs to isolated reefs which rise from deep-ramp settings. Evolution of the reef systems is being documented using seismic imaging, coring and U-series dating.
Scott Reef (at 14oS) is a macrotidal, isolated reef which overlies a carbonate platform and a major gas discovery. It has recently been the site of coral bleaching and studies of such disturbances are ongoing. Seismic profiles reveal a buried Last Interglacial (MIS5, ca.125,000 year) reef system, in contrast to the widely exposed reef of similar age along the Ningaloo coast, such that reefs which apparently grew to sea level are now 30m below present sea level, indicating significant subsidence in the Late Quaternary. Contemporary reefs grew during the Holocene (last 10,000 years) in the accommodation space provided by subsidence and are up to 35 m thick. These reefs have growth rates similar to those recorded for tropical reefs elsewhere.
New data have provided a greater understanding of the morphology and growth history of Scott Reef and the timing of sea-level events. The interaction of subsidence and glacial-interglacial sea-level change has resulted in multiple events of reef growth, each separated by periods of emergence and karstification, so that the reefs resemble a series of "stacked saucers" atop a 400m high carbonate platform.
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