Structural styles in the Perth Basin associated with the Mesozoic break-up of Greater India and Australia

Abstract

The Perth Basin constitutes one of the principal tectonic features along the western continental margin of Australia and formed through Permo-Cretaceous rifting of Greater India and Australia. It is composed of northerly striking sub-basins, troughs and ridges bounded by faults which display evidence for normal dip–slip, and possibly dextral strike–slip movement. Transfer faults divide the basin into compartmentalised regions of similar structural style. Extension and transtension occurred during the Jurassic–Early Cretaceous associated with continental break-up. Stretching was accommodated mainly by the reactivation of pre-existing northerly oriented faults which display both planar and listric geometries. The Darling Fault system along the eastern margin of the basin has a planar profile. The hanging wall succession in the adjoining Perth Basin has undergone block rotation and tilting with syn-sedimentary depositional thickening of rock units towards the fault. Listric normal faults occur in both the onshore and offshore portions of the basin and influence geometry of the sub-basins. Dip on these faults decreases through the basin sequence and probably soles out in the upper level of basement. Rollover anticlines develop within the hangingwall of these structures. Extension oblique to the main structural trends of the basin in the Late Jurassic–the earliest Cretaceous resulted in dextral strike–slip movement along major north-striking faults and the development of en-echelon folds in the basin. Compressive deformation developed during this event at constraining bends of the major fault systems. Two orientations of transfer zones are recognised and significantly influence basin structures. The first are east–west trending transfer faults which formed in the Permian and were reactivated during Jurassic extension but can only be recognised in the northernmost Perth Basin. These transfer faults link basin segments of different characteristics and transfer dip displacement among the northerly striking faults. The transfer zones striking NW only influence Late Jurassic–Early Cretaceous age deformation features. They are characterised by either a swing in a left-lateral sense in the orientation of northerly striking fractures as they cross the transfer zones or a termination of the fracture at the transfer zone. The transfer zones are parallel to, and may be related to, transform belts in the Indian oceanic crust. Basin-wide uplift occurred during the break-up and resulted in basin inversion and erosion of up to thousands of metres of the sedimentary succession. Folding by dextral strike–slip motion along the Darling-Urella fault system also inverted the pre-break-up sequences in major onshore depocentres.