Chapter in Geoscience Australia Record for Northern Yilgarn Seismic Workshop

Potential field data were used to constrain or support the geological interpretations of the 2006 and 2007 North Queensland seismic data. Potential field forward modelling, potential field inversions and worms of potential field data all supported the interpretations of the seismic data.

Labuan Basin lies in deep water adjacent to the eastern Kerguelen Plateau. The basin is about 800 km long and 300 km wide and contains up to 4.5 km of sediment. A general lack of geophysical data and geological samples in this remote basin have inhibited understanding of its stratigraphy and crustal origin. Our new seismic stratigraphic interpretation of the Labuan Basin is based on deep multichennel seimic data collected by Geoscience Australia in 1997 during "Rig Seismic" surveys 179 and 180 intergrated with results of Ocean Drilling Program (ODP) Leg 183 (1998-1999)

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No abstract available

In 1999, a grid of five deep seismic reflection traverses was acquired within an area approximately 50 km wide by 50 km long in the Kalgoorlie Region, Eastern Goldfields Province, Yilgarn Craton. The grid tied into the existing 1991 deep seismic reflection transect (EGF1) and the 1997 high resolution and regional seismic profiles acquired by the Australian Geodynamics Cooperative Research Centre (AGCRC) and Kalgoorlie Consolidated Gold Mines (KCGM). The data were acquired to examine the geometry of the major structural features of the region, particularly the highly mineralised Bardoc Shear, and to provide three-dimensional information on granites-greenstones relationships. This paper describes the geometry of the crust and, in particular, the geometry of the granite and greenstones above the prominent regional detachment surface that occurs at about 4-6 km depth, though in one place it may extend to a depth of approximately 11 km. From the seismic, the Bardoc Shear is confirmed as west dipping and a non-planar crustal penetrating structure. The gravity modelling suggests that there is no need for the large volumes of mafic or ultramafic material previously assumed to be at depth, apart from those mapped at the surface and projected to depth.

For the last 50 years, Geoscience Australia and its predecessors have been collecting onshore near-vertical-incidence deep seismic reflection data, first as low fold explosive data and more recently as high fold vibroseis data. These data have been used in conjunction with other seismic data sets by various research groups to construct depth to Moho models. The Moho has been interpreted either as a strong reflector per se, or as the bottom of a reflective band in the lower crust. However the amplitude standout of the Moho can be very much dependent on the fold of the data and applied processing sequence. Some low fold explosive data was re-processed by Geoscience Australia to enhance the Moho for comparison with recent vibroseis data, in the Mt Isa province in Queensland, and in the Southern Delamerian and Lachlan Fold Belts in Victoria. Marked improvement was achieved by time-variant band-limited noise suppression of reverberations, as well as by coherency weighted common mid point stacking. Post stack migration can also improve the clarity of the Moho, provided there is enough continuity of the data to avoid migration 'smiles'. An important consideration was amplitude scaling, with a time variant automatic gain control (AGC) employed before stack, and a weighted AGC applied after stack, in order to preserve seismic character. These results demonstrate that processing and acquisition issues need to be understood in order to assess the reflective character of the Moho and indeed to interpret its location.

New 2D seismic data acquired in the Mentelle Basin by Geoscience Australia in 2008-09 has been used for a seismic facies study of the post-rift succession. The Mentelle Basin is a large deep to ultra deep-water, frontier basin located on Australia's southwestern margin about 200 km southwest of Perth. The study focused on the post-rift sequences deposited following the breakup between Australia and Greater India. Stratigraphic wells DSDP 258 and DSDP 264 provide age and lithological constraints on the upper portion of the post-rift succession down to mid-Albian strata. The depositional environment and lithology of the older sequences are based on analysis of the seismic facies, stratal geometries and comparisons to the age equivalent units in the south Perth Basin. Fourteen seismic facies were identified based on reflection continuity, amplitude and frequency, internal reflection configuration and external geometries. They range from high continuity, high amplitude, parallel sheet facies to low continuity, low amplitude, parallel, subparallel and chaotic sheet, wedge and basin-fill facies. Channel and channel-fill features are common in several facies as well as a mounded facies (probably contourite) and its associated ponded turbidite fill. A progradational sigmoidal to oblique wedge facies occurs at several stratigraphic levels in the section. A chaotic mound facies, probably comprising debrite deposits, has a localised distribution. Seismic facies analysis of the post-rift sequences in the Mentelle Basin has contributed to a better understanding of the depositional history and sedimentation processes in the region, as well as provided additional constraints on regional and local tectonic events.

Between October 2008 and February 2009, Geoscience Australia undertook two major surveys off the coast of Western Australia. Areas of interest included the Mentelle and northern Perth Basins, the Southern Carnarvon Basin, the southern Exmouth Sub-basin (Northern Carnarvon Basin) and the Wallaby Plateau. These surveys collected a range of data, including industry-standard seismic reflection data and gravity and magnetic data. In addition to the new data collected, Geoscience Australia has reprocessed existing open file 2D seismic data within the survey area. These data are available for purchase. Please complete the order form on the downloadable information sheet and return to Geoscience Australia.

Abstract to be published as part of Seismix Conference Proceedings in a GA Record