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  • Legacy product - no abstract available

  • Legacy product - no abstract available

  • Geoscience Australia has recently conducted absolute gravity observations at Davis and Mawson stations in the Australian Antarctic Territory to establish accurate gravity reference points for past and future gravity surveys. These absolute gravity observations are the first such measurements undertaken at any of the Australian Antarctic stations and will not only provide an accurate absolute datum for future gravity work but will also enable gravity surveys that have already been conducted in the Australian Antarctic Territory to be tied to the same datum, thus allowing past and future gravity surveys to be accurately merged and combined.

  • The Capel and Faust basins lie at water depths of 1,500-3,000 m 800 km east of Brisbane. Geoscience Australia began a petroleum prospectivity study of these remote frontier basins with the acquisition of 2D geophysical data (seismic reflection, refraction, gravity, magnetic, multi-beam bathymetry) across an area of 87,000 km2 during 2006/07. The approach mapped the complex distribution of sub-basins and determined sediment thickness through integration of traditional 2D time-domain seismic interpretation techniques with 3D mapping, visualisation and gravity modelling. Forward and inverse 3D gravity models were used to inform the seismic interpretation process and test the seismic basement pick. Gravity models had three sediment layers with inferred average densities of 1.85, 2.13, 2.31 t/m3 overlying a pre-rift basement of density 2.54 t/m3, itself considered to consist of older basin material evidently intruded by igneous rocks. Conversion of travel times of interpreted seismic horizons to depth domain was achieved using a quadratic function derived from ray-tracing forward modelling of refraction data supplemented by stacking interval velocities, and densities for gravity modelling were inferred from the same velocity models. These models suggest sediment of average velocity 3.5 km/s reaches a thickness exceeding 6 km in the northwest of the area, and for the first time mapped the extent and depth of sediment in these basins. The results of the study have confirmed that sediment thickness in the Capel and Faust basins is sufficient in places for potential petroleum generation.

  • Many of the methods commonly used to calculate gravity anomalies have been around since the beginning of gravity surveying when calculations were done by hand and local horizontal and vertical datums were used. These days computing power is not a concern and most surveys are carried out using GPS technology with global datums. Geoscience Australia is reviewing the methods used to calculate gravity anomalies in the Australian National Gravity Database and is proposing changes such as the use of the GRS80 reference ellipsoid for calculating normal gravity and also as the height datum for anomaly calculations.