A unique grid of deep (12-14 second record length) seismic reflection and refraction
data was recorded by the Australian Geological Survey Organisation (formerly the
Bureau of Mineral Resources, Geology & Geophysics) across the offshore Gippsland
Basin and parts of the adjacent Bass Basin in 1988-1989. These data have been
interpreted to produce a new model for the development of the Gippsland and
adjacent Bass Strait basins as well as giving a greater understanding of the basins'
petroleum potential.
In general terms, the Gippsland Basin contains up to 16km of sediment in an ESE-trending
depocentre bounded on its north and northwestern margins by a
detachment ramp, and on its southern side by a relatively linear, listric fault system.
The basin, together with the adjacent Bass and Otway Basins, appears to have
formed as part of a linked, largely- strike-slip to 'transtensional' system, which
started to extend through Bass Strait, probably during the latest Jurassic. Each of the
basins developed by movement on a common detachment or detachment complex,
which produced headwall extension at their western ends, in the areas now occupied
by the Strzelecki Ranges, Otway Ranges - Torquay Sub-basin, and Robe Trough.
Adjustments and reactivation from the mid Cretaceous of several postulated
microplates in the region, largely in response to Tasman Basin rifting, gave rise to the
wrench-related and compressional structures which form the major petroleum targets
in the Gippsland Basin. However, the same process formed largely extensional
structures in the Bass Basin.
Our interpretation of the tectonic history of the Gippsland Basin leads us to the
conclusion that there may have been several phases of petroleum generation and
migration, and that potential petroleum traps appear to exist in the deeper section, in
structures sometimes not reflected at the top or near-top Latrobe Group levels.
