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New 2D seismic data acquired by Geoscience Australia in the northern Houtman Sub-basin of the Perth Basin provides important information on the prospectivity of this frontier area. To date, lack of quality seismic data and limited geological understanding have led to the perception that the hydrocarbon potential of the area is very low. However, interpretation of newly collected data suggests that the northern Houtman depocentre contains up to 15 km of pre-breakup sediments comprised of Permian, Triassic and Jurassic successions, which potentially contain multiple source rock, reservoir and seal intervals. The Permian syn-rift succession is confined to a series of large half-graben that are controlled by basement-involved faults separating the Houtman depocentre from the Bernier Platform. This succession is up to 10 km thick and is mapped throughout the inboard part of the new seismic grid. A prominent unconformity at the top of the Permian syn-rift sequence is overlain by a thick (up to 1800 m) and regionally extensive seismic sequence interpreted as the Lower Triassic Kockatea Shale. The thickness of the overlying Triassic succession ranges from approximately 1 km in the inboard part of the basin to up to 5 km further outboard. The Jurassic succession is thickest (up to 4 km) in the outboard part of the basin and is interpreted to contain sequences corresponding to the Cattamarra, Cadda and Yarragadee formations. Our study integrates new results from regional mapping, geophysical modelling and petroleum systems analysis, which enables a more accurate prospectivity assessment of this frontier basin.

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SUMMARYThe Houtman Sub-basin lies adjacent to the Wallaby-Zenith Transform Margin, an under-explored region of Australia's continental margin located at the transition between the non-volcanic margin of the northern Perth Basin and volcanic province of the Wallaby Plateau. New seismic data acquired in the northern Houtman Sub-basin enables better understanding of the structural architecture and rifting development along a rifted-transform margin and provides the framework for a detailed integrated margin-scale basin evaluation. Profile modelling of potential field data, combined with 2D seismic, reveals complex along-strike and dip variability in the crustal thinning of the Houtman Sub-basin, with extreme thinning (<5 km thick) beneath the main Permian depocentre. Outboard of this hyperextended zone, along the basin margin, is a zone of volcanic SDRs. Five different structural domains have been mapped across the margin, reflecting abrupt change in crustal thinning and volcanic emplacement. These domains trend roughly NW-SE to NNW-SSW, parallel to major basement terrane boundaries. Magnetic modelling suggests that the nature of the basement underlying the proximal domain and the hyperextended domain in the central Houtman Sub-basin are different and that a major Proterozoic basement terrane boundary lies beneath the necking domain. The margin was structured during polyphase Permian and Late Jurassic rifting events which led to hyperextension prior to continental magmatic break-up and formation of oceanic crust during the Early Cretaceous. Our results suggest that the distribution of Early Permian rifts localised strain during Jurassic-Early Cretaceous rifting and strongly controlled the location and style of rifted margin during Valanginian continental break-up.

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