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A Seismic-Based Structural Interpretation Of The Petel Sub-Basin, Bonaparte Gulf, Northern Australia.

Barnes, Craig Ronald

Honours Degree, 1994

University of Adelaide


A regional seismic interpretation of the Petrel Sub-Basin, Bonaparte Gulf, was undertaken to examine the structural development in Devonian to Cretaceous sediments and the influence of salt tectonics. The project was designed to review the development of the Bonaparte Rift and to determine the role of salt in the timing and growth rate of the Petrel and related Tern structures.

Seismic interpretation was conducted on 2000 km of high quality 14 second two way time data which allowed the Bonaparte Rift boundaries to be examined. Additional 5 second two way time seismic data were included to increase well control and highlight structural development of the Petrel Dome. Lineament interpretation was conducted on the Bouger Gravity Map of the area, as an aid to fault interpretation. A sandbox model analogue and a balanced cross section were compared to the interpreted seismic.

The fault interpretation arising from this study has shown four fault sets; NW-SE and N-S rift sets which dominate the fabric from the pre-Cambrian to the Early Permian, a NE-SW set formed by weak compression during the Permian, and an E-W disjoint accommodation zone which terminates to the south of the Tern structure. Fault interpretation upholds the current extensional theory of the region, with low fault activity at the Petrel and Tern localities. Remarkably few faults were mapped in the Permian to Recent section in the centre of the Sub-Basin. It could well be that dislocations in the basement are largely absorbed by a mobile evaporitic layer with the only response above being monoclinal flexures. Modelling suggests that the formation of the Petrel and Tern structures can be explained via salt removal from the basin.

Formation of the Petrel Dome was initiated in the Early Carboniferous and continued to the Early Permian. As salt moved during this period from the basin centre to the flanks, sediments collapsed into the region evacuated. The sediments become inverted when the bulk of the salt had migrated up the basin edges. Tern, a later structural feature than Petrel, could be a response to the `evaporite slug' moving up the western basin edge, with growth being prolonged by piercement diapirism during the Jurassic/Cretaceous.

The formation of structures in the Petrel Sub-Basin has been previously categorised as a near surface expression of deep crustal detachment faults. This study suggests that salt tectonics alone can explain the structures seen at Petrel and Tern.

Australian School of Petroleum



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