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Speculation is increasing that Proterozoic eastern Australia and western Laurentia represent conjugate rift margins formed during breakup of the NUNA supercontinent and thus share a common history of rift-related basin formation and magmatism. In Australia, this history is preserved within three stacked superbasins formed over 200 Myr in the Mount Isa region (1800-1750 Ma Leichhardt, 1730-1670 Ma Calvert and 1670-1575 Ma Isa), elements of which extend as far east as Georgetown. The Mount Isa basins developed on crystalline basement of comparable (~1840 Ma) age to that underlying the Paleoproterozoic Wernecke Supergroup and Hornby Bay Basin in NW Canada which share a similar tripartite sequence stratigraphy. Sedimentation in both regions was accompanied by magmatism at 1710 Ma, further supporting the notion of a common history. Basin formation in NW Canada and Mount Isa both concluded with contractional orogenesis at ~1600 Ma. Basins along the eastern edge of Proterozoic Australia are characterised by a major influx of sediment derived from juvenile volcanic rocks at ~1655 Ma and a significant Archean input, as indicated by Nd isotopic and detrital zircon data. A source for both these modes is currently not known in Australia although similar detrital zircon populations are documented in the Hornby Bay Basin, and in the Wernecke Supergroup, and juvenile 1660-1620 Ma volcanism occurs within Hornby Bay basin NW Canada. These new data are most consistent with a northern SWEAT-like tectonic reconstruction in a NUNA assembly thus giving an important constraint on continental reconstructions that predate Rodinia.

Out of Gondwana Marita Bradshaw, Jennie Totterdell, George Gibson, irina Borissova, John Kennard 'Out of Gondwana' is a chapter of the new book on Australia's geology being published by Geoscience Australia for the 34th International Geological Congress (IGC) to be held in Brisbane in 2012. As part of this book, Shaping a continent-building a nation: a geology of Australia, this chapter will tell the story of the break up and creation of Australia as the island continent, and how this unique geology has impacted the Australian people. Geoffrey Blainey recognises climate and distance as the two major influences on the historical development of Australia and Australians; and the 'tyranny of distance' was established with the separation from Gondwana. But the Gondwanan history has also bestowed resource riches - coal, gas and oil - which power the Australian economy today.

The Ord Valley Airborne Electromagnetics (AEM) Interpretation Project was undertaken to provide information in relation to salinity and groundwater management in the Ord River Irrigation Area (ORIA), and to guide its future expansion. The project included the acquisition of 5,936 line km of AEM data acquired using the SKYTEM time domain system, the acquisition of a Light Ranging and Detection (LiDAR) survey, and complementary drilling, borehole geophysics, laboratory analysis and interpretation services. Within the limits of available bore data and the scales of airborne data acquisition, this study provided greater spatial detail on critical elements of the hydrostratigraphy in the sedimentary alluvial aquifer systems. This included the indicative 3D extent and thickness of gravel, sand, silt, clay units as well as salt stores and groundwater quality. It also produced first generation of salinity hazard maps. The AEM mapping identified discrete palaeochannels, interpreted as elements of the palaeo-Ord drainage system. Overall, the amount and extent of gravel and sand aquifers present in the study area was significantly less than previously thought, with gravel aquifers present in laterally confined palaeochannel systems. There was also several buried bedrock ridges and shallow pediments that were interpreted to reduce aquifer storage and throughflow. In the Mantinea Plain-Carlton Hill-Parry's Lagoon area, the presence of a marine sand aquifer containing very saline groundwater was confirmed. The 3D mapping provided an important framework for hydrodynamic analysis and hydrogeochemical process studies. In summary, the project demonstrated the potential for 'calibrated' AEM systems and iTEM Fast Approximate Inversion software to shorten project timelines for studies that involve the analysis and interpretation of AEM data.

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Numerous Miocene reefs and build-ups have been identified in the Rowley Shoals region of the central North West Shelf, offshore Western Australia. The reefs form part of an extensive Miocene reef tract over 1600 km long, which extended northward into the Timor Sea and southwards to North West Cape. Growth of the vast majority of these Miocene reefs failed to keep pace with relative sea-level changes in the latest Miocene, whereas reef growth continued on the central North West Shelf to form the three present-day atolls of the Rowley Shoals (Mermaid, Clerke and Imperieuse Reefs). Widespread buildups and atoll reefs developed in the Rowley Shoals region in the Middle Miocene, and their internal stacking geometries indicate successive aggradational, progradational and back-stepping growth phases that are correlated with eustatic sea-level fluctuations. Growth of the majority of the Miocene reefs ceased at a major sea-level fall in the late Late Miocene, and only the reefs of the present-day Rowley Shoals continued to grow after this event. The Rowley Shoals reefs continued to keep pace with Pliocene-Pleistocene sea level changes, whereas the surrounding shelf subsided to depths of 230-440 m. Contrary to previous hypotheses, we find no direct evidence that active, or palaeo, hydrocarbon seepage triggered or controlled growth of the Rowley Shoals reefs or their buried Miocene predecessors. Rather we conclude that initial reef growth was controlled by transpressional reactivation and structuring of the Mermaid Fault Zone during the early stage of collision between the Australia and Asian plates.

Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available