The Houtman Sub-basin is an under-explored region of the northern Perth Basin, offshore Western Australia. Interpretation of Geoscience Australia’s recently acquired GA349 seismic survey reveals that the northern sub-basin contains a Permian–Early Cretaceous succession up to 16 km thick, dominated by two main phases of extension in the Permian and late Jurassic–Early Cretaceous. The most prominent feature of the basin architecture is a series of large Permian half graben which extend along the inboard part of the basin and are overlain by a westward-thickening Triassic–Jurassic succession with closely spaced faulting in the outboard region. To aid understanding of the basin’s petroleum prospectivity, this study uses 2D structural restorations to investigate the major phases of basin evolution, the amount of crustal extension (ß) associated with each rifting event and the magnitude of uplift and erosion associated with the Valanginian unconformity.
Newly interpreted seismic sequences were used to construct a 2D geological model on a dip line through the northern Houtman Sub-basin, which formed the basis of the structural restorations. A combination of decompaction and reconstruction using a simple shear kinematic model enabled regional restoration of the basin through time. Constraints on estimates of erosion at the Valangininian unconformity were provided by area balancing. 1D subsidence curves extracted along the section were compared with crustal thickness changes in the restored 2D profile to investigate the variation in extension factor along the transect.
Results indicate a complex basin history with multiple phases of rifting, culminating in the separation of Australia and Greater India. Initial Early- to mid-Permian rifting was focused along the inboard part of the basin, resulting in the formation of large half-graben and deposition of up to 10 km of synrift sediments. This was followed by widespread Triassic–Early Jurassic thermal subsidence. The second major phase of rifting occurred in the late Jurassic–Cretaceous and saw the focus of deformation shift to the outboard region of the basin. The total ß factor for both phases of extension is >6 over the outboard part of the basin, indicating hyperextension of the crust, with a maximum ß factor of 3 associated with Permian graben formation. The results of this work have important implications for petroleum potential in the basin. Crustal thinning and maximum burial depth are two key factors influencing the basin’s burial and temperature history, and hence are required for predicting source rock maturity and generation history.
