VIMP Report 17 - Seismic Interpretation of the Onshore Western Otway Basin, Victoria

Category: Victorian Initiative for Minerals and Petroleum Reports	Product Code: MP-R-27256
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Executive Summary As a result of a regional seismic interpretation of the onshore Otway Basin in western Victoria, two-way time formation top and thickness images were produced, in addition to a structural elements map showing age of faulting. These regional maps have been produced at 1:100 000 and 1:250 000 scales, and are tied into adjacent work carried out in South Australia and the eastern Otway Basin.

The work resulted in new models being proposed to explain the early development of the basin. These models involved rifting due, probably, to N-S extension in the Late Jurassic - Early Cretaceous, producing a number of half-graben on the northern margin of the basin. The rifting conforms with established rift development models in which half-graben of alternating vergence are separated by transfer zones displaying complex folding and faulting patterns. This rifting is interpreted to have ceased prior to the Aptian.

Within Victoria, the Penola Trough is mapped as an asymmetric graben, bounded in the north by the Kanawinka and Kanawinka South Fault Zones, and extending to the Penola South Fault Zone in the south. South of this fault zone thick Early Cretaceous sediments extend across the Mumbannar High. The Morenda and Tahara troughs are newly recognised half-graben on the northern margin of the basin.

An unconformity within the Wangerrip Group, coinciding with the onset of fast Southern Ocean spreading (52Ma) has been proposed.

During the Miocene and possibly earlier, compression resulted in right-lateral wrenching and inversion of previous faults.

A number of hydrocarbon play types have been identified based on the structural mapping carried out. These play types include anticlines associated with transfer zones, tilted fault blocks, buried basement highs, stratigraphic traps, post-Albian horst structures, syndepositional roll-over structures and Oligocene-Miocene normal and reverse fault related structures.

Bibliographic reference Perincek, D., Simons, B., Pettifer, G. & Gunatillake, K., 1995. Seismic interpretation of the onshore Western Otway Basin, Victoria. Victorian Initiative for Minerals and Petroleum Report 17. Department of Agriculture, Energy and Minerals.