The increasing availability of 3D seismic data from sedimentary basins at volcanic and non-volcanic continental margins has provided fundamental new insights into both the storage and transport of magma in the continental crust. As global hydrocarbon exploration increasingly focuses on passive margin basins with evidence for past intrusive and extrusive igneous activity, constraining the distribution, timing and pathways of magmatism in these basins is essential to reduce exploration risk. Producing and prospective Australian passive margin basins where igneous systems have been identified include the Bight, Otway, Bass, Gippsland and Sorell basins of the southern margin. This paper reviews both the impacts of volcanic activity on sedimentary basin hydrocarbon prospectivity (e.g. advective heating, reservoir compartmentalisation and diagenesis), and the styles, distribution and timing of late Cretaceous-Recent extrusive and intrusive igneous activity along basins of the southern Australian margin, providing illustrative examples based on 2D and 3D seismic reflection data. KEYWORDSAustralia, sedimentary basins, volcanics, intrusives, seismic reflection, petroleum systems. INTRODUCTIONThe past few decades have witnessed a progressive shift of focus in the quest for new conventional hydrocarbon resources, away from the onshore and shallow-water regions that dominated production throughout the 20th century, and towards the submerged and often deep-water (>500 m below sea level) continental margins that fringe the deep ocean basins (White et al, 2003). Although exploration of all hydrocarbon basins is subject to problems (Doré et al, 2002), exploration of continental margins poses major risks due to the significant geological uncertainties that stem from sparse data coverage and their poorly understood formation and evolution. An important geological risk associated with exploration in almost all continental margins is the presence of igneous rocks. Volcanic activity is a key outcome of lithospheric stretching processes (Planke et al, 2000), and thus all extensional sedimentary basins located along continental margins witness some degree of intrusive and extrusive activity during their life spans. This includes basins that are located along margins considered to be 'cold ' , or 'nonvolcanic' (White et al, 2003).Hydrocarbon exploration has traditionally overlooked or avoided basins containing igneous rocks (Schutter, 2003; Rohrman, 2007). This is mainly because of the difficulties associated with seismic imaging of sedimentary sequences beneath basalt covers, and the detrimental short-term and long-term impacts on petroleum systems, including reservoir degradation and compartmentalisation (Schutter, 2003; Planke et al, 2005; Rohrman, 2007). The depletion of reserves in traditional hydrocarbon provinces, however-coupled with improvements in seismic acquisition and processing methods in basins containing problematic high-impedance layers (e.g. basalts)-has led to increasing exploration activity, with some not...

The Late Cretaceous Ceduna Delta is the largest deltaic system on the Australian continent, yet its source is unknown. Apatite fission-track data reveal widespread Late Cretaceous exhumation across the southern Australian margin. New detrital zircon analysis of 786 grains from the Gnarlyknots-1 well, which penetrated the offshore delta top, show that the upper part of the delta (Santonian–Maastrichtian) was sourced largely from recycled Permian to Early Cretaceous cover and underlying basement eroded from the margin, proximal to the basin. This challenges the widely accepted model involving distal provenance of >2000 km from the eastern margin of Australia. Supplementary material The 2D seismic reflection data, results for detrital zircon LA-ICP-MS and zircon fission-track analyses, including the LA-ICP-MS method, and a list of sample intervals and ages are available at www.geolsoc.org.uk/SUP18582 .

High‐quality, long offset seismic data from many distal rifted margins show evidence for hyper‐extended, <10‐km‐thick crust. Direct observation of such domains is challenging as they lie, at great water depth, buried beneath thick sedimentary sequences and formed by rock‐assemblages that are hydrated and geophysically indistinguishable. Only a few drill holes have penetrated basement at ultradistal rifted margins. These observations, together with outcrops of preserved analogs exposed in collisional orogens, suggest that the complex interaction of detachment faults rooted in a subhorizontal shear zone in the hyperextended crust or, in the serpentinized mantle controls the formation of the ocean continent transition. While depth‐dependent thinning controls the early phases of rifting conforming to classical rift models, we still have a superficial understanding of how normal faults and subhorizontal shear zones form and evolve during rifting and lithospheric breakup. Here we develop a rheological parameterization to simulate the formation of, and slip‐on, large offset normal faults rooted in growing brittle to ductile shear zones. The evolution of these structures leads to the creation of a hyperextended crust and eventually exhumed serpentinized mantle. We also propose a simplified formulation to simulate magmatic underplating and seafloor spreading. The resulting numerical models provide a self‐consistent picture for the evolution of magma‐poor rifted margins from initiation of rifting to seafloor spreading. The model results are compared with first‐order observations of the Kwanza and Espirito Santo conjugate margins in the South Atlantic as well as of magma‐poor margins globally.

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We present results from a margin-wide analysis of the history of post-breakup Cenozoic compressional deformation and related exhumation along the passive southern margin of Australia based on a regional synthesis of seismic, stratigraphic and thermochronological data. The Cenozoic sedimentary record of the southern margin contains regional unconformities of intraLutetian and late Miocene-Pliocene age, which coincide with reconfigurations of the boundaries of the Indo-Australian Plate. Seismic data show that post-breakup compressional deformation and sedimentary basin inversion, characterised by reactivation of syn-rift faults and folding of post-rift sediments, is pervasive from the Gulf St Vincent to Gippsland basins, and occurred almost continually since the early-to-mid Eocene. Inversion structures are absent from the Bight Basin which we interpret to be the result of both the unsuitable orientation of faults for reactivation with respect to post-breakup stress fields, and the colder, stronger lithosphere that underlies that part of the margin. Compressional deformation along the southeastern margin has mainly been accommodated by reactivation of syn-rift faults resulting in folds with varying ages and amplitudes within the post-rift Cenozoic succession. Many hydrocarbon fields in the Otway and Gippsland basins are located within these folds, the largest of which are often associated with substantial localised exhumation. Our results emphasise the importance of constraining the timing of Cenozoic compression and exhumation in defining hydrocarbon prospectivity of the southern margin.