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  • AGSO's northwest Australian margin project (NWAM) aims to provide a high level understanding of the geological framework of the entire northwest margin of the continent, with particular emphasis on the crustal and basin architecture. The following studies are currently addressing these objectives: 1) ArcView GIS, 2) Potential field and bathymetric grids (2nd version), 3) Regional deep seismic re-interpretation, and 4) Ocean-bottom seismograph velocity models.

  • High quality refraction and wide-angle reflection seismic data recorded by ocean-bottom seismographs (OBSs) deployed by the Australian Geological Survey Organisation along the 700 km long transect in the Carnarvon Basin effectively supplement results obtained by means of the conventional reflection technology. Velocity information can now be derived from both CDP (nearvertical reflection) and OBS (refraction/wide-angle reflection) data. Generally, CDP-derived average velocities are lower than OBS-derived velocities and this deviation increases with depth: from ~0.1 km/s at 8 s two way time (TWT) to 0.8-1.6 km/s at 16 s TWT. If the CDP-derived velocities are used to depth convert reflection data, then depth to these TWTs would be underestimated by 0.4 to 6.4-12.8 km respectively. Some local anomalies (at ~6s TWT CDP-derived velocities may be more than 0.1 km/s higher than the OBS-derived velocities) distort this general trend. These would result in ~0.3 km local overestimates of the depth equivalent of 6s TWT. Co-analysis of the interval velocity field reconstructed from the travel time-based interpretation of the OBS data and the conventional reflection image of the crust in some cases shows their poor correlation.

  • Geology interpreted from geophysics. The map shows Archaean geology plus magnetic units in overlying cover rocks.

  • This paper was presented at 15th AGC - Understanding Planet Earth, Sydney, July 2000

  • This paper was presented at 15th AGC - Understanding Planet Earth, Sydney, July 2000

  • Biosiliceous sediments sampled from a submarine valley system on the continental shelf of East Antarctica contain intervals of ripple cross-lamination interspersed with massively bedded units. Based on radiocarbon dates from one core collected on the Mac.Robertson Shelf, the most intensely cross-laminated sediments were deposited between 6 000 and 3 500 years before the present, with isolated cross-laminae deposited at other times in the Holocene.

  • The product comprises digital outcrop geology and interpreted basement geology layers in ArcInfo, MapInfo and ArcView formats. The data were compiled from geological mapping of the Condobolin 100K sheet from 1997 to 1999 by the NSW Geological Survey and AGSO under the NGMA. The data layers are a subset of the Forbes 250K sheet GIS data package.

  • We have demonstrated for the first time the application of a small angle neutron scattering (SANS) technique for the precise determination of the onset of hydrocarbon transport (primary migration) in shaly source rocks. We used a sequence of rocks pyrolysed in the laboratory under nitrogen at temperatures in the range 310-370°C. These rocks contained several percent of dispersed marine Type II organic matter. Geochemical analysis indicated a peak of the hydrocarbon generation in the middle of the temperature range (at 340°C). We observed a sharp decrease of SANS intensity in a narrow maturity range within the geochemically determined region of the onset of hydrocarbon generation. This decrease was a direct consequence of the SANS contrast variation caused by the invasion of the pore space by bitumen during the primary migration of hydrocarbons. A similar phenomenon was observed for a natural maturity sequence of source rocks originating from the same location.