No abstract available

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No abstract available

In review Jan 2001 (internal)

This is an extended abstract prepared for the Mines and Wines conference run by SMEDG_GSNSW_AIG in Orange, NSW on 18-21 September 2007.

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Flexural backstripping applied to 5 seismic reflection lines has been used to constrain the distribution of lithosphere thinning, crustal structure and the location of the ocean-continent transition (OCT) of the southern Australian Bight Basin rifted margin. The amplitude of the anomalous subsidence in the southern margin of Australia was determined for each seismic line by means of residual depth anomalies (RDA) and included in all models. Sensitivity tests of predicted syn-breakup melt generated during lithosphere thinning and breakup were investigated assuming a magma-poor and a normal non-volcanic margin. The Bight Basin shows an apparent crustal segmentation between the Eyre-Recherche and the Ceduna-Recherche sub-basins. Whilst the lateral variation of lithosphere thinning in the Ceduna-Recherche sub-basin is gradual, in the Eyre-Recherche it is abrupt, predicting a highly extended continental crust underneath the Recherche sub-basin. Predicted ocean-continent transition (OCT) widths for the Bight Basin range from approximately 100 km to a maximum of 200 km, although the structure of the OCT itself is unclear. The predicted OCT determined from flexural backstripping compared with independent estimates of basement thickness derived from gravity inversion are in general agreement. Linear marine magnetic anomalies appear to be lying within the predicted OCT of the Bight Basin. If the magnetic anomalies are due to the presence of highly serpentinized peridotites and mafic bodies, the magnetic lineations cannot be used to constrain conventional seafloor spreading.

Petroleum exploration within the Gippsland Basin has been focussed on major anticlines at the Early Tertiary "top Latrobe"unconformity, and to a much lesser extent on "intra-Latrobe" traps. Little information exists on the petroleum potential deep within the basin. Similarly, in the adjacent Bass Basin, most of the exploration effort has been concentrated at or near the top of the Latrobe Group equivalent, the Eastern View Coal Measures. Analysis of regional seimic data collected by BMR in 1982 suggests that the Bass and Gippsland Basins were initiated by NNE-SSW lithospheric extension, probably in the Early Cretaceous. A reactivation of these basin-forming extensional structures, particularly transfer faults, may have had a significant influence on petroleum migration and accumulation higher in the stratigraphic section. This operational report describes the first of two cruises to be undertaken by the R/V Rig Seismic in the Gippsland/Bass region(Nov - Dec.1988 & March - April 1989). These cruises aim to: (i) improve definition of the deep structure of the Gippsland and Bass Basins using basin-wide deep seismic (12+ seconds) transects, (ii) evaluate models for basin evolution (iii) develop concepts for petroleum migration andentrapment from the regional data and by analogy with the similar basins worldwide, and (iv) through the provision of regional seismic data assist the petroleum industry in carrying out seismic correlations. The cruises contribute to a number of studies by BMR of the structure, stratigraphy, evolution and resource potential of offshore basins along Australia's southeastern margin. This first cruise (Survey 82) was broken into four parts: (1) Equipment testing for future work: involving the measurement of drift on a HIfix radio navigation system, and testing IFP electronics for the deep recording objectives of the program, (ii) Recording of approximately 470 km of relatively deep-water reflection profiles in the eastern Gippsland Basin (12s records, 52.4 litre air-gunarray for Line 82/001 , 26.7 litre for lines82/002 & 3). (iii) Recording of 1090 km of seismic reflection profiles in a grid over the Boobyalla Sub-basin of the Bass Basin (mainly 10s records, 26.7litre air-gun array). (iv) Shooting of 2 x 200km refraction lines across the central part of the Gippsland basin from Deal Island to the Victorian coast.

The Browse Basin underlies the outer shelf and upper slope of the central part of Australia'sNorth West Shelf, in water depths of 100-1000 m. Although the North West Shelf is generallyconsidered to be one of Australia's most heavily explored offshore regions, there aresignificant portions of it, such as the offshore Canning and Browse Basins, that remain under-explored. Relatively little is known of the primary structural architecture of the basin systemsof the North West Shelf, and the influence of that architecture on the occurrence ofhydrocarbons. The Browse Basin study (AGSO Project 121.28 - Basin development andhydrocarbon potential of the Browse Basin and adjacent margin) is part of a major AGSOregional research program over the north western Australian margin, and has the following main objectives: 1) Determine the regional structural framework of the Browse Basin and its relationship toadjacent features such as the Vulcan Sub-basin, Rowley Sub-basin, Scott Plateau andKimberley Block; 2) Define the broad deep-crustal structure of the region and develop a model explaining the tectonic, subsidence and thermal history of the basin in relation to the development of thecontinental margin and adjacent ocean basin (the Argo Abyssal Plain); 3) Assess the effects of deep structure and reactivation on the development of knownpetroleum accumulations. To address these objectives it is proposed that RV Rig Seismic be used to acquire about 3200km (up to a maximum of 3600 km depending on contingencies) of deep seismic and othergeophysical data along 11 lines tying 18 exploration wells in the Browse Basin/Scott Plateauregion. The survey will also tie into the 1990 Vulcan Sub-basin survey (98) to the northeast,and the forthcoming survey over the offshore Canning Basin to the southwest. In line with the Marine Geoscience and Petroleum Geology Program's (MGPGP's) most recentdeep seismic surveys over the North West Shelf, the Browse Basin survey will use a 4800 mstreamer, configured with 192 x 25 m active groups; data will be recorded with a 16 secondrecord length, and a 2 millisecond sample interval; the seismic source will be dual airgunarrays with a total capacity of 49 litres, and will be fired every 50 metres to give 48-fold CDPcoverage; and navigation will be by differential GPS. These parameters are the same as usedon two surveys over the northern Carnarvon Basin (SNOWS-1 and SNOWS-2) and threesurveys over the Bonaparte Basin - Timor Sea, and will also be used on the SNOWS-3 surveyover the offshore Canning Basin, following the Browse survey. Using these parametersAGSO has consistently recorded reflections down to 8-12 seconds two-way time (12-20 kmdepth), as well as obtaining good resolution in the upper 6 seconds of data, which is normallythe limit recorded by industry.

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