The Capel and Faust basins lie at water depths of 1500-3000 metres, 800 km east of Brisbane. Geoscience Australia began a petroleum prospectivity study of these remote frontier basins with acquisition of reflection and refraction seismic, gravity, magnetic and multi-beam bathymetry data across an area of 87,000 km2 during 2006/07. The approach mapped a complex distribution of sub-basins through an integration of traditional 2D reflection seismic interpretation techniques with 3D mapping and gravity modelling. Forward and inverse gravity models were used to inform the ongoing reflection seismic interpretation and test the identification of basement. Gravity models had three sediment layers with average densities inferred from refraction velocity modelling of 1.85, 2.13, 2.31 t/m3 overlying a pre-rift basement of density 2.54 t/m3, itself considered to consist in part of intruded older basin material. Depth conversion of horizon travel times was achieved using a function derived from models of refraction data. Gravity modelling of the simple density model arising from the initial interpretation of reflection seismic data indicated a first order agreement between observed and calculated data. The second order misfits could be accounted for by a combination of adjustments to the density values assigned to each of the layers, localised adjustments to the basin depths, and heterogeneity in the basement density values. The study concluded that sediment of average velocity 3500 m/s exceeds 6000 m thickness in the northwest of the area, which is sufficient for potential petroleum generation.

The Early Permian to Middle Triassic Bowen and Gunnedah basins in eastern Australia developed in response to a series of interplate and intraplate tectonic events located to the east of the basin system. The initial event was extensional and stretched the continental crust to form part of the major Early Permian East Australian Rift System that stretched at least from far north Queensland to southern New South Wales. The most commercially important of the rift-related features are a series of half graben that form the Denison Trough, now the site of several producing gas fields. The eastern part of the rift system commenced at about 305 Ma and was volcanic dominated. In contrast, the half graben in, and to the west of, the Bowen Basin were non-volcanic, and appear to have initiated at about 285 Ma. These half graben are essentially north-south in length with an extension direction of approximately east-northeast. Mechanical extension appears to have ceased at about 280 Ma, when subsidence became driven by thermal relaxation. The extension occurred in a backarc setting, in response to far field stresses that propagated from the west-dipping subduction system at the convergent plate margin of East Gondwana that was located to the east of the East Australian Rift System.

The Bremer Sub-basin, which forms part of the Bight Basin off the southern coast of Western Australia, is a deep-water (100-4000 m water depth) frontier area for petroleum exploration. No wells have been drilled to test the sub-basin's petroleum potential, with company exploration limited to a regional seismic survey by Esso Australia Ltd in 1974. Early studies identified the Bremer Subbasin as a series of Middle Jurassic-Early Cretaceous half graben, which contain potentially prospective structures for trapping hydrocarbons. However, a lack of sub-surface geological data, along with the deep-water setting, discouraged exploration of this area for over 30 years. In 2003, the Bremer Sub-basin was identified as a key frontier area in Geoscience Australia's New Oil Program where new exploration opportunities might occur. Subsequently, Geoscience Australia's Bremer Sub-basin Study commenced in 2004 with an aim to determine if the sub-basin formed under suitable geological conditions to generate and trap large volumes of hydrocarbons.

Geological framework of the South Tasman Rise and East Tasman Plateau: structure, tectonics, basin development

This document will be posted on the GA and CSIRO-Marine websites. Dr. Neville Exon was Chief Scientist and Cruise Leader for this survey.

The seismic stacking velocity data in the Great Australian Bight are a useful dataset for calculating depths and sediment thicknesses. This work compares these data with P-wave velocities from sonobuoys and sonic logs from wells, and on this basis a depth over-estimate of at least 15% can be expected from the depths derived from stacking velocities. Megasequence boundary depths are calculated for the Ceduna Terrace to further illustrate data quality. The database makes avaliable the unfiltered stacking velocities using conventional and horizon-consistent formats.

A new sequence stratigraphic framework has been developed for the Otway Basin based on the interpretation and integration of offshore wells, key onshore wells, new biostratigraphic results and a regional grid of 2D seismic data. In the new tectonostratigraphic framework, seven major basin phases and their eight component supersequences are recognised as follows: 1) Tithonian?-Barremian rifting of the Crayfish Supersequence 2) Aptian-Albian post-rift deposition of the Eumeralla Supersequence 3) mid-Cretaceous compression and inversion 4) Late Cretaceous rifting of the Shipwreck and Sherbrook Supersequences 5) latest Maastrichtian to Middle Eocene basin reorganisation and early thermal subsidence of the Wangerrip Supersequence 6) local inversion and thermal subsidence of the Nirranda Supersequence (Middle Eocene to Early Oligocene) followed by thermal subsidence and progressive compression of the Heytesbury Supersequence (Late Oligocene to Late Miocene) leading to Late Miocene uplift and erosion and 7) Plio-Pleistocene deposition of the Whalers Bluff Supersequence. Basin phases are distinguished by their different tectonic driving mechanisms as the primary control on the creation of accommodation space. The supersequences are bounded by regional unconformities and define major episodes of sedimentation within each basin phase. Supersequences are related to second-order transgressive-regressive cycles within the basin and are regionally mappable. The new sequence stratigraphic framework is then used as the basis for correlation to deep-water regions where well-control is limited or absent. The framework is also used to help place existing, complex, facies-dependent lithostratigraphic schemes into depositional and petroleum systems context.

The 4-10 km-thick Bangemall Supergroup, comprising the Edmund and Collier groups, was deposited between 1620 Ma and 1070 Ma in response to intracratonic extensional reactivation of the Paleoproterozoic Capricorn compressional orogen. The supergroup can be further divided into six depositional packages bounded by unconformities or major marine flooding surfaces. Samples of each of the major sandstone units within these packages have been collected for detrital zircon provenance analysis. U-Pb dating of over 1200 detrital zircon grains has failed to identify any syndepositional magmatism, but provides an extensive dataset for evaluating the provenance history of the Bangemall Supergroup and implications for the Mesoproterozoic paleogeography of the West Australian Craton. Integration of this detrital zircon data with palaeocurrent data indicates that all source areas were located within the Mesoproterozoic West Australian Craton, with the main source area for the northern Bangemall Supergroup being the Gascoyne Complex and southern Pilbara Craton. All samples have prominent age modes in the 1850-1600 Ma range, indicating significant contribution from the northern Gascoyne Complex and coeval sedimentary basins. Some samples also display prominent modes in the 2780-2450 Ma range, consistent with derivation from the Fortescue and Hamersley groups. The provenance history of the Edmund Group records unroofing of the underlying basement, from the Gascoyne Complex to the Archean granites and greenstones of the Pilbara Craton. This results in detrital age-spectra in which the dominant modes become older upwards. In contrast, the Collier Group records unroofing of the underlying Edmund Group, and is characterized by age-spectra in which the dominant modes become younger upwards. These data imply that the West Australian Craton remained intact throughout the Mesoproterozoic assembly of Rodinia, and was the only source of detritus for the Bangemall Supergroup. Keywords: Bangemall Supergroup, Edmund Group, Collier Group, paleocurrents, provenance, zircon

This paper presents tectonic elements maps for the continental margin of East Antarctica, from 38-164E, together with brief descriptions of all the major tectonic elements.

This report (Record 2009/38) contains the description and preliminary analysis of datasets acquired during Geoscience Australia marine reconnaissance survey GA2476 to the west Australian margin. The survey, completed as part of the Federal Government's Offshore Energy Program, was undertaken between 25 October 2008 and 19 January 2009 using the German research vessel RV Sonne. The survey acquired geological, geophysical, oceanographic and biological data over poorly known areas of Australia's western continental margin. Data from the marine reconnaissance survey (GA2476) and the concordant regional seismic survey (GA0310) will improve knowledge of frontier sedimentary basins and marginal plateaus and allow assessment of their petroleum prospectivity and environmental significance. These data will be used to improve resource management and underpin decisions regarding future acreage release in offshore Western Australia and marine zone management. Four key areas were targeted: the Zeewyck and Houtman sub-basins (Perth Basin), the Cuvier margin (northwest of the Southern Carnarvon Basin), and the Cuvier Plateau (a sub-feature of the Wallaby Plateau). Over the duration of the survey a total of 229,000 km2 (26,500 line-km) of seabed was mapped with the multi-beam sonar, 25,000 line-km of digital shallow seismic reflection data and 25,000 line-km of gravity and magnetic data. A variety of sampling equipment was deployed over the duration of the survey, including ocean floor observation systems (OFOS), deep-sea TV controlled grab (BODO), boxcores, rock dredges, conductivity-temperature-depth profilers (CTD) and epibenthic sleds. A total of 62 stations were examined throughout the survey, including 16 over the Houtman Sub-basin, 16 over the Zeewyck Sub-basin, 13 in the Cuvier margin, 12 over the Cuvier Plateau and four in the Indian Ocean. This report is intended to provide a comprehensive overview of the survey activities, equipment used and preliminary results form survey GA2476.