Extensional Basin — Forming Structures in Bass Strait and Their Importance for Hydrocarbon Exploration

Abstract

The Bass, Gippsland and Otway Basins of southeastern Australia were initiated by north-northeast to south- southwest lithospheric extension, largely during the Early Cretaceous. The extensional stage was followed by a Late Cretaceous to Pliocene thermal subsidence stage and a late stage of compressional tectonic overprinting.The extensional stage was dominated by two orthogonal fault sets - shallow to moderately dipping, rotational, normal faults and steeply dipping, transfer (transform) faults. Thermal subsidence involved vertical rather than horizontal movements, and consequently generated a discrete fault geometry, comprising steep, down-to-basin, normal faults with small displacements. The major extensional structures exerted a range of controls on both sedimentation and structuring during the subsidence stage. Likewise, the location and style of late Tertiary compressional structures overprinted on the Gippsland and, to a lesser extent, Bass and Otway Basins are controlled by reactivation of major early normal and transfer faults. In particular, the Kingfish, Mackerel, Halibut, Flounder and Tuna fields in the Gippsland Basin overlie a single Early Cretaceous transfer fault zone that was a basinwide structural boundary during extension. These fields occupy en echelon compressional structures generated by left-lateral wrench reactivation of the transfer zone during late Tertiary northwest-southeast compression. The major extensional structures have had an important influence on all stages of the evolution of these basins. It is contended that a thorough understanding of their extensional framework is an important factor in hydrocarbon exploration of these and other basins.

Cenozoic fault control on ‘deep lead’ palaeoriver systems, Central Highlands, Victoria

“…The southeast Australian margin records Cretaceous and Cenozoic extension associated with Australia/ Antarctica/Lord Howe Rise breakup and opening of the Southern Ocean/Tasman Sea (Etheridge et al 1985;Veevers et al 1991 et al 2003). In most of these papers, the evidence of tectonism is clear, but the reasons for compressional events at this time less so.…”

No mountains to snow on: major post-Eocene uplift of the East Victoria Highlands; evidence from Cenozoic deposits

“…The southeast Australian margin records Cretaceous and Cenozoic extension associated with Australia/ Antarctica/Lord Howe Rise breakup and opening of the Southern Ocean/Tasman Sea (Etheridge et al 1985;Veevers et al 1991 McGowran et al 2004). The onset of fast ocean spreading at this time is generally considered to be a major cause of the unconformities, but Perincek & Cockshell (1995) believed the northeast -southwest-trending faults in the eastern Otway Basin derived from post-Oligocene compressional structures when Cretaceous east -west trends became inactive and were replaced by northeast-trending faulting during the Miocene.…”

“…In the Gippsland Basin, they are considered initiated by Early Cretaceous syn-rift extension as a result of Australia -Antarctica rifting (Etheridge et al 1985;Veevers 1991;Hill et al 1994;Perincek & Cockshell 1995). East-northeast-and northeast-oriented structures are present on the margins of the South Gippsland (Strzelecki) Hills, in the Latrobe Valley, and on many structures in the offshore parts of the basins.…”

Inversion of a transfer system into lateral ramps: An example from the South-Central Pyrenees (Spain)

“…In this paper we attempt to show the kinematic role of pre-existing transfer faults, which are common in extensional systems (Etheridge et al 1985;Gibbs 1989;Russell and Snelson 1990;Tankard et al 1989).…”