The Early Cretaceous South Perth Shale has been previously identified as the regional seal in the offshore Vlaming Sub-basin. The South Perth Shale is a deltaic succession, which unfilled a large palaeotopographic low in the Early Cretaceous through a series of transgressive and regressive events. The new study undertaken at Geoscience Australia has shown that the seal quality varies greatly throughout the basin and at places has very poor sealing properties. A re-evaluation of the regional seal based on seismic mapping determined the extent of the pro-delta shale facies within the South Perth Shale succession, which are shown to provide effective sealing capacity. New sequence stratigraphic interpretation, seismic facies mapping, new and revised biostratigraphic data and well log analysis were used to produce palaeogeographic reconstructions which document the distribution of depositional facies within the South Perth Shale Formation and reveal evolution of the Early Cretaceous deltas. Our study documents spatial variations in the seal quality and re-defines the extent and thickness of the regional seal in the central Vlaming Sub-basin. It provides an explanation for the lack of exploration success at some structural closures and constraints for possible location of the valid plays.

Speculation is increasing that Proterozoic eastern Australia and western Laurentia represent conjugate rift margins formed during breakup of the NUNA supercontinent and thus share a common history of rift-related basin formation and magmatism. In Australia, this history is preserved within three stacked superbasins formed over 200 Myr in the Mount Isa region (1800-1750 Ma Leichhardt, 1730-1670 Ma Calvert and 1670-1575 Ma Isa), elements of which extend as far east as Georgetown. The Mount Isa basins developed on crystalline basement of comparable (~1840 Ma) age to that underlying the Paleoproterozoic Wernecke Supergroup and Hornby Bay Basin in NW Canada which share a similar tripartite sequence stratigraphy. Sedimentation in both regions was accompanied by magmatism at 1710 Ma, further supporting the notion of a common history. Basin formation in NW Canada and Mount Isa both concluded with contractional orogenesis at ~1600 Ma. Basins along the eastern edge of Proterozoic Australia are characterised by a major influx of sediment derived from juvenile volcanic rocks at ~1655 Ma and a significant Archean input, as indicated by Nd isotopic and detrital zircon data. A source for both these modes is currently not known in Australia although similar detrital zircon populations are documented in the Hornby Bay Basin, and in the Wernecke Supergroup, and juvenile 1660-1620 Ma volcanism occurs within Hornby Bay basin NW Canada. These new data are most consistent with a northern SWEAT-like tectonic reconstruction in a NUNA assembly thus giving an important constraint on continental reconstructions that predate Rodinia.

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A high resolution sequence stratigraphic study has been undertaken on the three wells in the Houtman Sub-basin, offshore North Perth Basin: Gun Island 1 (1968), Houtman 1 (1978) and Charon 1 (2008). The study focussed on the late Jurassic Yarragadee Formation, mid Jurassic Cadda Formation and early Jurassic Cattamarra Coal Measures. Log character (particularly gamma ray and sonic), cuttings, sidewall core and conventional core lithologies (including sedimentary structures) and palynological data were used to identify paleoenvironments. Stacking patterns of the interpreted environments were used to define systems tracts and then sequences. New palynological data have been collected by Geoscience Australia for Gun Island 1 and the palynology for all wells has been reviewed from Well Completion Reports and slides from intervals in each well. A number of transgressive systems tracts within the dominantly continental Yarragadee Formation and Cattamarra Coal Measures record small marine incursions into the Houtman Sub-basin. Within these units, the shallow marine intervals switch rapidly with non-marine intervals suggesting a more dynamic environment existed in the Houtman Sub-basin during the Jurassic than previously thought. These marine incursions are not evident in the Yarragadee Formation in Charon 1, indicating a lack of accommodation space or proximal sediment input into the north during the mid-late Jurassic. This has significant implications for reservoir and seal facies of potential Mesozoic petroleum systems in the Houtman Sub-basin.

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Palaeogeographic reconstructions of the Australian and Antarctic margins based on matching basement structures are commonly difficult to reconcile with those derived from ocean floor magnetic anomalies and plate vectors. Following identification of a previously unmapped crustal-scale structure in the southern part of the Delamerian Orogen (Coorong Shear Zone), a revised plate reconstruction for these margins is proposed. This reconstruction positions the Coorong Shear Zone opposite the Mertz Shear Zone and indicates that structural inheritance had a profound influence on the location and geometry of continental breakup, and ocean fracture development. Previously, the Mertz Shear Zone has been correlated with the Proterozoic Kalinjala Mylonite Zone in the Gawler craton but this means that Australia is positioned 300-400 km too far east relative to Antarctica prior to breakup. Differences in the orientation of late Jurassic-Cretaceous basin-bounding normal faults in the Bight and Otway basins further suggest that extensional strain during basin formation was partitioned across the Coorong Shear Zone following an earlier episode of strike-slip faulting on a northwest-striking continental transform fault (Trans-Antarctic Shear).

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The greater Phoenix area in the Bedout Sub-basin has experienced recent exploration success on Australia’s North West Shelf (NWS). Oil and gas discoveries in the Triassic reservoirs of the Keraudren Formation and Locker Shale have revived interest in mapping the distribution and lateral facies variation of the Triassic succession from the Bedout Sub-basin into the adjacent underexplored Beagle and Rowley sub-basins. This multi-disciplinary study integrating structural architecture, sequence stratigraphy, palaeogeography and geochemistry has mapped the spatial and temporal distributions of Triassic source rocks on the central NWS. The Lower‒Middle Triassic palaeogeography is dominated by a deltaic system building from the Bedout Sub-basin into the Beagle Sub-basin. The oil sourced and reservoired within the Lower‒Middle Triassic sequences at Phoenix South 1 is unique to the Bedout Sub-basin, compared to other oils along the NWS. Its mixed land-plant and algal biomarker signature is most likely sourced locally by fluvial-deltaic mudstones within the TR10‒TR14 or TR15 sequences and represents a new petroleum system on the NWS. A Middle Triassic marine incursion is recorded in the Bedout Sub-basin with the development of a carbonate platform while in the Rowley Sub-basin, volcanics have been penetrated at the top of the thick Lower‒Middle Triassic sediment package. The Late Triassic palaeogeographic map suggests a carbonate environment in the Rowley Sub-basin distinct to the clastic-dominated fluvial-deltaic environment in the Beagle Sub-basin. This information combined with results of well-based geochemical analyses highlights the potential for hydrocarbon generation within the Upper Triassic in these sub-basins. This extended abstract was presented at the Australasian Exploration Geoscience Conference (AECG) 2019

Palaeogrographic analysis of the Early Cretaceous South Perth Supersequence.

During the period 1984-1996, AGSO compiled and produced a series of Palaeogeographic atlases of Australia for the Phanerozoic Eon. The Atlases - Cambrian, Ordovician, Silurian, Permian, Jurassic, and Cainozoic - contained maps which summarised the most important sedimentological data extracted from a wide variety of sources. Due to time and resource constraints four Periods (Devonian, Carboniferous, Triassic and Cretaceous) were not published, although data were compiled. Atlases consisted of a series of Data and Interpretation maps a Structure map, and supporting Stratigraphic Columns and text. Maps were compiled at a scale of 1:5 000 000 and digitally produced using MicroStation CAD software. The PALAEOGEOGRAPHIC ATLAS OF AUSTRALIA dataset has resulted from the conversion of the CAD atlas maps from all ten atlases into a format compatible with GIS applications. Important CAD elements such as lithology patterns have been retained for visualisation purposes. It is envisaged that this Palaeogeographic dataset will become part of the AGCRC Australia's Geodynamic Framework project.