This Record presents a new stratigraphic interpretation of Cretaceous sedimentary rocks encountered in petroleum exploration wells, stratigraphic holes and water bores along the southern Australian coast in Western Australia and South Australia. The Cretaceous succession in these wells is interpreted within the Bight Basin sequence stratigraphic framework, and is correlated with the thicker section farther basinward. The correlation is based on existing and recently commissioned biostratigraphic data, and the interpretation of seismic data on the continental shelf. The onshore wells contain a sedimentary section ranging in age from Valanginian to Campanian, and attributable to the Bronze Whaler, Blue Whale-White Pointer, Tiger and Hammerhead supersequences. The succession reaches a maximum thickness of more than 357 m in the Madura 1 well. The section preserved in these wells records the evolution of depositional environments near the northern margin of the Bight Basin, from areally restricted non-marine deposition in the Early Cretaceous, through increasingly marine, although shallow and anoxic, conditions, to the local development of a small deltaic complex in the Late Cretaceous. Organic-rich non-marine shales of Early Cretaceous age, and Late Cretaceous organic-rich facies of marine affinity have been identified in wells in the study area., providing new information about the nature and extent of potential source rocks in the Bight Basin.

INTRODUCTION In 2006, the Prime Minister announced A$134 million in Commonwealth Government funding for Geoscience Australia as part of the Australian Government's Energy Security Initiative. The funding extends from 2006 until 2011 and includes A$76.4 million to expand Geoscience Australia's Offshore Energy Security Program to identify new hydrocarbon provinces. As part of this program, a new tectono-stratigraphic and petroleum systems study has been carried out in the Vlaming Sub-basin on Australia's southwest continental margin. The study has included revising the biostratigraphy for key wells, interpreting new and reprocessed seismic data, a new geochemical assessment of key source rock intervals and recovered liquid petroleum, structural restoration and 3D burial history modelling. Results have significantly improved our understanding of the Vlaming Sub-basin's evolution and provide a basis for future exploration. New exploration opportunities in the southern Vlaming Sub-basin are open to explorers through the Commonwealth Government's 2008 Acreage Release. ACREAGE RELEASE AREAS WA08-23 AND WA08-24, VLAMING SUB-BASIN, PERTH BASIN The Vlaming Sub-basin is an elongate, north-south trending depocentre that lies within the continental shelf and upper slope (0-1000 m water depth) in the offshore southern Perth Basin (Figure 1). Acreage release areas WA08-23 and WA08-24 are located in the southern part of the basin, which has had limited previous exploration. During initial exploration activity in the 1970s to early 1980s, reasonable 2D seismic coverage was acquired over most of the sub-basin and 16 wells were drilled. However, except for a non-commercial oil discovery at Gage Roads 1, all wells drilled on potential 4-way closure prospects were unsuccessful. This halted exploration activity for almost two decades. Subsequent analysis has shown that exploration failure in the Vlaming Sub-basin was due to inadequate seismic coverage and therefore poor structural definition of prospects (Miyazaki et al., 1996). An uptake of acreage in the Vlaming Sub-basin in 2005 started a new round of exploration activity in the northern and central parts of the sub-basin. At present, NEXUS holds one permit (WA-368-P) and ROC OIL two permits (WA-381-P and WA-382-P). Both companies are in the process of acquiring or have planned to acquire new seismic data with commitments drill one well in each permit. In 2008 two new areas are being released in the southern Vlaming Sub-basin (WA08-23 and WA08-24). Since the non-commercial oil discovery at Gage Roads 1, exploration activity has been focused in the northern part of the sub-basin. The southern part is more structurally complex and has a higher proportion of sandstones in its syn-rift section. Only two wells have been drilled in this area: Sugarloaf 1 (1971) and Felix 1 (1998), both failing to find any indications of hydrocarbon. Seismic coverage in this part of the basin is relatively sparse (Figure 2) and older vintages of seismic data tend to be of poor quality and low resolution. However, active petroleum systems present in the northern Vlaming Sub-basin are likely to extend to the south where there is potential for hydrocarbon accumulations.

The Late Santonian to Maastrichtian Hammerhead Delta represents an extended period dominated by deltaic deposition during the Late Cretaceous in the Ceduna Sub-basin. This study presents new seismic stratigraphic data and interpretations for the large shelf-margin delta complex that formed in the Ceduna Sub-basin.

Data from 50 sonobuoys were recorded over the Capel and Faust Basins, 800 km to the east of Australia in water depths 1500-2000 m, during a 2006/07 seismic survey (GA302) for Geoscience Australia's New Oil initiative. These data were interpreted and forward modelled by ray-tracing to provide an estimate of P-wave velocities in the upper sedimentary section, and hence constrain estimates of sediment thickness. Also recorded were gravity and magnetic anomaly data which, in conjunction with the very high quality seismic reflection data, provided additional constraints upon the velocity models. The preliminary seismic reflection records studied are typified by four sets of reflection patterns: I) a ~500m thick sequence just below sea floor, II) a highly reflective flat-lying set of reflectors of variable thickness lying unconformably over III) a discontinuous, dipping, deformed sequence penetrated by high-amplitude events, and IV) deepest sequence generally marked by onset of high amplitude events. Typical ranges in four model layers below water were: 1.9, 2.3-3.0, 3.6-4.7, 5-5.3 km/s. Gravity models based on these results were compared to features identified on depth converted seismic reflection lines and indicate that sediment thickness at densities approximating 2.3 t/m3 (typically including sequences I-III) may reach 5 km in several localities.

Conference volume and CD are available through the Petroleum Exploration Society of Australia

A new tectonostratigraphic framework for the southern Bowen, Gunnedah and Surat basins in New South Wales is developed, based on the sequence stratigraphic and structural interpretation of regional reflection seismic data, and petroleum and stratigraphic wells. This framework provides an improved correlation between the Bowen and Gunnedah basins, and delineates the relationship between tectonic events, basin phases, and the development of depositional sequences. The Early Permian Cretaceous depositional history of the basins in this region was controlled by successive phases of tectonic subsidence driven by extension, thermal relaxation and lithospheric flexure, interrupted by periods of contraction and uplift. Early Permian extension was characterised by the eruption of volcanic rocks and the accumulation of dominantly lacustrine sediments, followed by the deposition of thick coal-conglomerate successions, particularly along the eastern margin of the basin. The succeeding thermal subsidence phase was quickly overwhelmed by flexural subsidence driven by foreland loading during the Early Late Permian, and the deposition of marine, deltaic and non-marine rocks. Late Permian contraction and uplift in the Gunnedah Basin was followed by the accumulation of non-marine Triassic rocks derived from the New England Orogen. A dominantly fluvial Middle Triassic succession is present across the entire region. Effects of the Middle Late Triassic contractional event that is evident throughout the Bowen Gunnedah Sydney basin system were concentrated along the basin-bounding Goondiwindi, Kelvin and Mooki faults and also adjacent to the Boggabri Ridge

The principles of non-marine sequence stratigraphy were applied to the Jurassic strata in the lower part of the Surat Basin, in order to better determine the depositional history of the basin and highlight potential reservoir and source rocks. The lithostratigraphic units in the Early Late Jurassic interval can be divided into three supersequences: J, K, and L. Each supersequence consists of a basal sandstone-dominated unit generally exhibiting an unconformable, diachronous relationship with the underlying unit. This is the lowstand system tract (LST), which potentially offers an extensive well-sorted sandstone reservoir with interconnected porosity. These amalgamated sandstone sheets are overlain by a fining-upward interval consisting of predominantly muddier carbonaceous lithologies including coal and lacustrine deposits. This upper sequence embraces the transgressive system tract (TST) and possibly the highstand system tract (HST). Isolated meander-belt sandstone bodies may be preserved within these widespread finer deposits and provide reservoirs juxtaposed to source rocks. Vitrinite reflectance values indicate that these Jurassic units are immature to marginally mature and, hence, may only have limited hydrocarbon generating prospects

No abstract available

Paleoproterozoic-earliest Mesoproterozoic sequences in the Mount Isa region of northern Australia preserve a 200 Myr record of intracontinental rifting and consequent passive margin formation. Passive margin formation followed a switch in the extensional direction from ENE-WSW to NE-SW ca. 1740 Ma, and was accompanied by extensional unroofing of 1670 Ma magmatic rocks from mid-crustal depths. The resulting asymmetries in basin geometry and crustal architecture represent a first-order constraint on reconstructions of Rodinia that juxtapose Proterozoic eastern Australia against rocks of comparable age in western Laurentia.

The warm greenhouse world of the Late Cretaceous created an ocean that was poorly stratified latitudinally and vertically. Periodically these oceans experienced globally significant events where oxygen minimum zones enveloped the continental margins. Evidence of the effect of one of these Ocean Anoxic Events (OAE?s) is preserved in the southern high latitude strata of the Otway Basin in southeast Australia. During the Late Cretaceous, thick sequences of mudstone-dominated deltaic sediments (the Otway Delta) were deposited in an elongate inlet (ca. 500km wide) between Antarctica and Australia located at least 70?S. The initial Turonian strata of this delta (the Waarre Formation) were deposited in marginal marine delta plain to delta front conditions. The overlying Flaxman Formation and basal Belfast Mudstone preserve evidence of transgressive inner to middle shelf upper delta to prodelta conditions. These Turonian units were subject to periodic dysoxia. The conditions that created this dysoxia in the region were similar to those of the high northern latitude Cretaceous Interior Seaway of North America where intermittent freshwater input and deepening seas caused periods of thermohaline stratification and reduced bottom waters. The overlying Coniacian to Santonian Belfast Mudstone was deposited in outer shelf to upper slope prodelta conditions subject to periodic fluctuations in dysoxia with normal marine salinities. After a period when the oxygen minimum zone contracted, upward-increasing dysoxia in the Belfast Mudstone herald the onset of the Coniacian to Santonian OAE 3. This was the last OAE of the Late Cretaceous, prior to the onset of more ?modern? oceanic conditions. The fluctuations in TOC and hydrogen index in these strata reflect variable dysoxic conditions similar to that reported for OAE 3 in the tropical eastern Atlantic by Hofmann et al. (2003). This periodicity implies a very active and dynamic Late Cretaceous hydrosphere. Eventually, hyposaline conditions or higher sedimentation rates due to upper delta progradation and shallowing in the Santonian caused the local extinction and dissolution of many of the calcareous benthic taxa of the Belfast Mudstone.