Legacy product - no abstract available

The Ceduna Sub-basin of the deep-water frontier Bight Basin contains a Middle Jurassic-Late Cretaceous sedimentary succession in excess of 15 km thick. Nine offshore exploration wells have been drilled in the basin, mostly clustered around the inboard edge of the Ceduna Sub-basin. As a result, the distal mid-Late Cretaceous strata predicted to contain potential source rock facies, had previously not been sampled. The presence of high quality source rocks in the basin was therefore an open question. 2D seismic data was used to delineate targets for sampling of the pre-Campanian section of the basin. Identified targets included potential source intervals of Albian-Santonian age at locations on the seaward edge of the Ceduna and Eyre Terrace where canyon formation, slumping and faulting have exposed the section. Also, a series of sites were selected to test for potential hydrocarbon seepage in the basin. These sites include areas where recently reactivated deep-seated faults were exposed at the seafloor, basin margin areas where facies thin, and areas where possible seepage was identified from Synthetic Aperture Radar (SAR) data. In February and March 2007, a 3-week marine acquisition programme was carried out on the RV Southern Surveyor. Potential dredge targets were first surveyed with 30 kHz EM300 swath bathymetry and observed with Topaz 3.5 kHz sub-bottom profiler. Near-live swath processing and slope analysis techniques enabled site specific dredge sampling of seafloor terrains where Cretaceous section outcropped or slopes were sufficient to ensure only a thin cover of overlying sediments. Targets include fault scarps and eroded sides of canyons. A better-than-expected number of successful dredges were collected (total of 37) from water depths ranging from 1600-4500m. Geochemical analysis of 259 dredge samples for total organic carbon (TOC) and pyrolysis yields (Rock Eval) identified good to very good organic richness in 13 samples, with TOC values between 2.1% and 6.2%. Of these, seven show liquids potential with Hydrocarbon Index (HI) values ranging between 274 and 479 (mgHC/TOC). The rocks with the best source rock characteristics came from high priority sampling sites in the westernmost Ceduna Sub-basin. Organic geochemical analysis has provided evidence for preservation of organic matter under anoxic conditions close to or at the sediment-water interface. Biostratigraphic analysis of these organic-rich rocks has yielded an age around the Cenomanian-Turonian boundary. Although the dredged rocks are immature for hydrocarbon generation, interpretation of an extensive seismic grid across the basin and petroleum system modelling have shown that this succession occurs with the oil window in the central Ceduna Sub-basin. The results of this study provide the best evidence to date for the presence of good quality liquids-prone source rocks in the basin, successfully addressing a key industry concern in this petroleum exploration frontier.

Poorly exposed Paleoproterozoic sandstones and siltstones of the Killi Killi Formation record developement of a large turbidite complex. Killi Killi Formation sediments were eroded from the uplifted ~1860 Ma Nimbuwah and Hooper Orogens as indicated by detrital zircons with sediment deposition at ~1840 Ma. Facies analysis, isopach maps and detrital zircon populations, combined with Sm-Nd data from the Tanami region and Halls Creek Orogen, confirm the previously suggested correlation of the Paleoproterozoic successions in the Eastern zone of the Halls Creek Orogen and the Tanami region. Detrital zircons from the Aileron Province suggest the turbidite complex extends into the Arunta region, however, high metamorphic grade precludes direct facies comparisons in the Arunta region. Portions of the turbidite complex in the Tanami region are dominated by mudstones, consisting of low-density turbidites and associated hemipelagites, that potentially acted as a redox boundary to gold-bearing fluid. Gold prospectivity in turbiditic systems is increased within these mudstone sequences with the potential for further gold discoveries.

Extended abstract to accompany oral conference presentation. Full version of the short abstract (GEOCAT 70799).

A movie flythrough displaying various geological and geophysical data used for petroleum prospectivity assessment of the offshore northern Perth Basin

Geodynamic modelling of selected aspects of the Bowen, Gunnedah, Surat and Eromanga basins constrains the mechanisms that were operating during their formation. For the Bowen and Gunnedah basins, a quantitative analysis of the early Late Permian to Middle Triassic foreland loading phase examined the relative roles of static loading versus dynamic loading associated with the convergent plate margin. Subsidence in the initial foreland phase in the early Late Permian is consistent with platform tilting due to corner flow in the mantle associated with west-directed subduction. Later in the Late Permian, platform tilting probably continued to be the dominant cause of subsidence, but increasing amounts of subsidence due to foreland loading occurred as the thrust front in the New England Orogen migrated westward. In the latest Permian and Early Triassic, static flexural loading due to foreland loads is dominant and may be the sole cause for basin subsidence. For the Surat and Eromanga basins, the tectonic subsidence across an east-west transect is modelled to assess the contribution of dynamically-induced platform tilting, due to viscous mantle corner flow, in basin subsidence. The modelling suggests that subsidence was again controlled by dynamic platform tilting, which provides a mechanism for both the nearfield and farfield effects. Uplift of the Eastern Highlands in the mid-Cretaceous may also be related to viscous corner flow driven by west-directed subduction beneath eastern Australia, with the uplift being due to rebound of the lithosphere after the cessation of subduction.

The Onshore Energy Security Program, funded by the Australian Government, has been a five year program (2006-2011) conducted by Geoscience Australia in conjunction with the Australian state and Northern Territory geological surveys. Its aim was to provide new geological information on frontier onshore sedimentary basins in Australia, and, as part of this program, deep seismic reflection data have been acquired across several basins, to provide fundamental information on the stratigraphic and structural architecture of the basins and to stimulate hydrocarbon exploration. Reflection data were acquired over the Darling, Arrowie, Georgina (Queensland and Northern Territory), Amadeus, Arckaringa, Officer (Western Australia and South Australia) and southern Carnarvon Basins. This program also discovered and imaged a previously unknown basin, the Millungera Basin, in northwestern Queensland. Ranging from the Neoproterozoic to Cretaceous, these basins encompass segments of the Centralian Superbasin and later phases of basins that have built the Australia continent. Key results of this work include description of the architecture and internal geometries of each basin, settings imaged include mostly extensional basins, many which are later subject to contraction either by inversion (Arrowie Basin) or thrusting (Amadeus Basin) and, an example of a strike-slip basin, the Moorilyanna Graben, in the Officer Basin. The interpretation of stratigraphy used a sequence stratigraphic approach providing a basis for 1D petroleum systems modelling of the Millungera, Arrowie, Georgina (QLD) and Darling Basins. In total, 10 deep seismic profiles across 8 basins have been interpreted, hopefully contributing to an increase in onshore exploration activity.

Abstract for initial submission, pending acceptance by convention technical program committee.

Many aspects of the evolution and overall architecture of the Australian southern rifted margin are consistent with current models for the development of non-volcanic rifted margins. However, when examined in detail, several key features of the southern margin provide useful points of comparison with the Atlantic and Alpine Tethyan margins from which these models derive. Extensive petroleum industry and government seismic and geophysical data sets have enabled detailed mapping of the basins of the southern margin and an improved understanding of its tectonostratigraphic evolution. Australia's southern rifted continental margin extends for over 4000 km, from the structurally complex margin south of the Naturaliste Plateau in the west, to the transform plate boundary adjacent to the South Tasman Rise in the east. The margin contains a series of Middle Jurassic to Cenozoic basins-the Bight, Otway, Sorell, Gippsland and Bass basins, and smaller depocentres on the South Tasman Rise (STR). These basins, and the architecture of the margin, evolved through repeated episodes of extension and thermal subsidence leading up to, and following, the commencement of sea-floor spreading between Australia and Antarctica. Break-up took place diachronously along the margin, commencing in the west at ~83 Ma and concluding in the east at ~ 34 Ma. In general, break-up was not accompanied by significant magmatism and the margin is classified as 'non-volcanic' (or magma-poor). Initial NW-SE ultra-slow to slow seafloor spreading (latest Santonian-Early Eocene), followed by N-S directed fast spreading (Middle Eocene-present), resulted in: (1) an E-W oriented obliquely- to normally-rifted marginal segment extending from the westernmost Bight Basin to the central Otway Basin; (2) an approximately N-S oriented transform continental margin in the east (western Tasmania-STR), and (3) a transitional zone between those end-members (southern Otway-Sorell basins).

The paper discusses the results from the GA-302 2D seismic survey and GA-2436 (RV Tangaroa) marine reconnaissance survey over the Capel and Faust basins, northern Tasman Sea. The integration of seismic, potential field and bathymetric data sets in 3D space at an early stage in the project workflow has assisted in the visualisation of the basin architecture, the interpolation of data between the seismic lines, and the iterative refinement of interpretations. The data sets confirm the presence of multiple depocentres, as previously interpreted from satellite gravity data, with a maximum sediment thickness of 5-7 km. Preliminary interpretation of the seismic data has identified two predominantly Cretaceous syn-rift and two Upper Cretaceous to Neogene sag megasequences overlying a heterogeneous pre-rift basement. The comparison of seismic facies and tectonostratigraphic history with offshore New Zealand and eastern Australian basins suggests the presence of possible Jurassic to Upper Cretaceous coaly and lacustrine source rocks in the pre- and syn-rift, and fluvio-deltaic to shallow marine reservoir rocks in the syn-rift to early post-rift successions. Preliminary 1D basin modelling suggests that the deeper depocentres of the Capel and Faust basins are within the oil and gas windows. Large potential stratigraphic and structural traps are also present.