The offshore Roebuck Basin is an amazingly complex and unexpected piece of North West Shelf geology. Large scale seismic geometries within the Triassic section is interpreted to define a complex of lava deltas associated within even a bigger scale rift complex. The location of the magmatic outpouring can be associated with a failed triple junction. Gravity and magnetic modelling supports this model and the apparent thickness of the volcanic complex is up to 10km. The impact of this rifting is felt regionally along the three arms of the proposed triple junction. The northern arm is easily identified and extends up to the proto-Barcoo and proto-Caswell sub-Basins. The eastern arm propagates with strike-slip motion through the Fitzroy Trough creating numerous transpressional and transextensional features in the Palaeozoic and Early Triassic stratigraphypreviously known as the Fitzroy Movement. The western arm is only recognised to the north of Wombat Plateau. In this area, the Early Triassic thins dramatically and sets up the uplifted outboard edge of a broad epicentre extending across the present-day Northern Carnarvon Basin. The sequences described above across all three arms are overlain by a major unconformity that is interpreted to be a product of these rifting/uplift events. This paper highlights that a regional approach, incorporating data from multiple sources, geographical areas and formations, assists with the broader understanding of tectonic history of the North West Shelf during the Early Triassic to Middle Triassic.

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Using dispersants to mitigate oil spills has remained controversial, despite considerable testing, in both the laboratory and the field. One of the major concerns, which has not been satisfactorily resolved, is how effective various dispersants are on different oils over a range of environmental conditions. Laboratory experiments cannot accurately simulate the real world, while field experiments are difficult to monitor and control. To eliminate some of the problems previously encountered when testing dispersants, an experiment was conducted in a large (approximately 30 m × 55 m × 2.5 m deep) outdoor wave test basin. The main objective of the experiment was to test the action of Corexit 9527 on unweathered Issungnak crude oil in low energy, nonbreaking waves. Eight tests were conducted, four on control oil slicks and four on treated slicks. The oil was contained in a 4.6 m diameter boom with a 1.85 m deep skirt. The boom was moored at one end of the test basin 6 m from a wave generator, which could generate waves up to 0.4 m high. At the opposite (shallow) end of the wave basin, a gravel beach absorbed the energy of the waves. For each test, the wave generator was run for about 4 hours, with a constant wave height (set from 10 to 28 cm) and period (1.6 s). During this time, water samples were drawn at regular intervals from various depths for measuring oil concentrations in the water column. The data indicated that, in 10 and 20 cm nonbreaking waves, dispersion of oil into the water column from an untreated oil slick was negligible. During all the experiments for treated slicks, concentrations of oil in the boom were dramatically higher than for untreated slicks. Even in quiescent conditions, concentrations as high as 4 ppm were observed at 50 cm after 24 hours under a treated slick. Concentrations of up to 60 ppm were observed at 50 cm in the water column in 10 cm waves. Investigations of oil drop size showed that under the treated slicks the oil droplet diameters ranged from 1 µm to 8 µm diameter. Overall, the results showed that, even in low energy waves, there was a significant increase in dispersion from a surface slick of unweathered Issungnak oil when it was treated with Corexit 9527, and the oil in water emulsion formed was more stable than that from an untreated slick.