Deep Structure of the Gippsland and Bass Basins (Project 9131.12). Operational Report for Cruise 1 (Survey 82)

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.

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