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A pilot project conducted in October 1991, from Rig Seismic (AGSO Survey 104), utilising the continuous geochemical tracer [CGT] capability, showed that theanalyses of oceanic waters for light hydrocarbon content provides a useful method for characterising pollutants from various sources (BMR Research Newsletter, 16). The offshore Sydney component of Survey 104 was conducted between Botany Bay and North Head. Light hydrocarbon anomalies were detected from each of the three deepwater ocean outfalls operated by the Water Board. The results suggested that the molecular compositions of different hydrocarbon mixtures may be useful indicators of hydrocarbon 'sources' mixed together in the coastal zone. A reprint of the BMR Research Newsletter article of the pilot survey is reproduced in Figure 1.1. The usefulness of the CGT equipment, demonstrated during that pilot project, resultedin an additional survey (Survey 112), conducted on Rig Seismic during September/October 1992 (Heggie et al., 1992), which combined scientific staff from AGSO and the Water Board (Sydney). Scientific activities on Survey 112 included: (i)seafloor sampling, to gather environmental baseline information on the nutrient and contaminant (heavy metals and organochlorines) status of sediments, and also sedimentology of the nearshore region and, (ii) water column analyses, comprising approximately 500 line-km of CGT data (light hydrocarbons in seawater complemented with temperature, salinity, dissolved oxygen and pH) collected in the vicinity of the deepwater ocean outfalls. The purposes of this Record are to: (i) provide a description of the edited hydrographic (temperature and salinity), oxygen and pH data and, (ii) combine these data with some of the light hydrocarbon (DHD) data. Sediment and DHD data collected during Survey 112 are addressed in other AGSO Records (Heggie et al., 1993a; Heggie et al., I993b). A separate part of Survey 112, conducted with scientific staff from Sydney University, the NSW Geological Survey and the Ocean Sciences Institute, between Newcastle and Wollongong provides a regional context for thoseobservations focussed about Sydney. The preliminary results of that part of Survey 112 are included in Bickford and Heggie et al. (1993).

The Townsville Basin (new name) is an extensional basin which underlies the Townsville Trough, an east-west trending bathymetric feature separating the Marion and Queensland Plateaus off northeastern Australia. The present study forms part of a wider study of the regional stratigraphic and structural framework of Australia's northeastern margin undertaken as part of AGSO's Continental Margin Program. It is the first integrated study of a regional seismic grid across the Townsville Basin, and details the results of the interpretation of 5667 km of AGSO and industry seismic reflection data across the area. With the exception of several ODP holes which intersected Late Miocene to Recent sediments, there is no direct control on the stratigraphy of the Townsville Basin. The maximum sediment thickness in the basin reaches approximately 4.5 s TWT (::::: 6.5 km). The sedimentary fill can be subdivided into two main seismic megasequences, a synrift and a sag-phase megasequence. The synrift megasequence has a maximum thickness of up to 2 s TWT (::::: 2 km) and occurs in fault-controlled depocentres. The sag-phase megasequence occurs as drape fill and reaches a thickness of up to 2.6 s TWT (::::: 3.8 km). The two megasequences have been subdivided into regionally mappable sequences. An early synrift sequence can be distinguished in deeper half-graben. This is overlain by a regionally more extensive synrift sequence and a late-rift sequence. The early sag-phase sequences are thin or absent in the western Townsville Basin, but thicken into the central basin. The three overlying sequences consist of terrigenous and calcareous sediments of Neogene age, and are separated from the underlying section by a ?mid-Oligocene regional unconformity. Depth to basement, total sediment thickness, synrift isopach and gravity data all indicate that the underlying rift-forming structures compartmentalise the basin into distinct sub-basins which are separated by major north-northwest to northwesttrending transverse structural zones. These transverse structures are associated with distinct changes in structural trends and are thought to represent major preexisting crustal-scale terrane boundaries or shear zones. Overall, the structural style of the Townsville Basin is characterised by a half-graben morphology with occasional, apparently asymmetric graben structures. The half-graben are bounded by major rotational normal faults and are typically composed of a number of tilt blocks. The basin boundaries are defined by switches between steep normal faults and gently dipping hinges. An important feature of the Townsville Basin is the presence of northwest to north-northwest trending lineaments which generally offset half-graben bounding faults in a right-lateral sense along the basin margins. The rotational normal faults are compartmentalised by these lineaments which are interpreted as transfer fault zones or accommodation zones. Local thickening of late rift sediments in the opposite direction to that of the early rift sediments probably reflects at least two significant extensional structuring events during basin formation. A younger wrenching event, which occurred during early sag-phase sedimentation, was followed by ?Late Miocene to Early Pliocene reactivation events. The structural interpretation of the Townsville Basin confirms that it formed part of a complex rift system of probable Late Jurassic to Early Cretaceous age. This system formed through oblique extension which utilised pre-existing Palaeozoic structural trends. Comparison with interpreted structural trends of the adjacent Queensland Basin (Queensland Trough) supports the suggestion that formation of both basins was independent of the tectonism related to seafloor spreading in the Tasman and Coral Sea Basins.

Exploration in the offshore northern Carnarvon Basin during the last two decades has resulted in a number of major oil and gas discoveries. Recent discoveries in the Dampier (di Toro, 1994; Delfos, 1994), Exmouth (Bauer et al., 1994; Lawry & Carter, 1994; Mitchelmore & Smith, 1994) and Barrow (Beacher et al., 1994; Sit et al., 1994) sub-basins ensure that exploration activity is likely to remain high in these areas for the near future. However, some of these discoveries have been small fields or individual wells with residual oil columns, indicating that still greater quantities of hydrocarbons have escaped from the traps. Recent work on oil-filled fluid inclusions (Lisk & Eadington, 1994) indicates that the loss of hydrocarbons from pre-Cretaceous reservoirs and traps occurred during the past 20 million years, beginning in the Miocene. These hydrocarbons may have been lost, but could potentially have been trapped in younger Cretaceous and Tertiary reservoirs. The Carnarvon Cretaceousflertiary Tie study proposes to address this issue by collecting and interpreting a regional high-resolution seismic survey, within the broad structural and tectonic framework provided by the Continental Margins Program Northwest Shelf Project. The main objectives are: 1) construction of a regional, sequence-based chronostratigraphic framework for the Cretaceous and Tertiary within which the occurrence and distribution of potential seal and reservoir facies may be analyzed and predicted; 2) assessment of the post-Valanginian fault reactivation history of the northern Carnarvon Basin and the implications for: (a) the migration of hydrocarbons from pre-Cretaceous traps and (b) the integrity of potential Cretaceous and Tertiary seals; 3) determination of the probability of secondary migration and entrapment of hydrocarbons within Cretaceous and Tertiary strata. Approximately 4240 krn of high-resolution seismic data has been proposed for acquisition by AGSO's RV Rig Seismic. The data set will comprise 23 seismic lines tying 107 wells in the Exrnouth, Barrow, Dampier and Beagle Sub-basins. These data will tie with and complement the deep-seismic grid previously acquired by AGSO in the Carnarvon Basin. The seismic survey will be acquired using the latest high-resolution seismic technology. Data will be recorded using bubble-free GI air guns and with the following parameters: 3000m streamer; 12.5m group interval, 18.75m shot interval, recording frequency bandwidth of 4- 180Hz; 2ms sample interval; 5.5 second record length; and 80-fold CDP multiplicity. The program layout includes 5 strike lines linking the Exrnouth, Barrow, Dampier and Beagle subbasins and 18 dip lines orthogonal to the principal Mesozoic sub-basin fault systems.

Legacy product - no abstract available

Seismic Test Survey conducted by the Bureau of Mineral Resources, Geology andGeophysics (BMR) (now Australian Geological Survey Organisation (AGSO)) during the early part of 1989. The objective of the survey was to test the suitability of the seismicreflection technique for proposed regional deep reflection seismic lines in the Gunnedah Basin and Cobar Basin. The major emphasis of the test survey was to assess the feasibility of acquiring shallow and deep seismic reflections in order to examine various geologicalmodels of bounding faults and basin structure. The survey acquired data from five sites in the Gunnedah Basin and three sites inthe Cobar Basin. The quality of data in the deeper part of the sections, i.e. 6-15 seconds (TWT), varied from very good to excellent. Seismic reflections in the sedimentary part ofthe succession were, in general, very poor, but some surprisingly good seismic reflectionevents were obtained below the Pilliga Sandstone in the Gunnedah Basin. The test survey indicated that the deep seismic reflection technique in theGunnedah Basin and Cobar Basin would provide data that would be of assistance in developing new geological models, and an understanding of fault geometries and basinstructure, and would assist the exploration for mineral and petroleum resources in the future.

The Bureau of Mineral Resources, Geology & Geophysics (BMR) (now Australian Geological Survey Organisation (AGSO)), Department of Primary Industries & Energy, Australian Government, conducted the Bowen Basin Seismic Survey during July to October 1989. The major aim of the seismic survey was to record deep seismic reflection data across the northern part of the Bowen Basin, to test geological (extensional) models for the formation of the Bowen Basin. The locations of the seismic lines were determined in consultation with exploration companies and the Department of Resources Industries (now Dept. of Minerals & Energy),Queensland State Government. The requirement that the seismic lines be targeted andconstrained to follow a proposed geological corridor was a controlling factor in thepositioning of the seismic lines. The deep seismic reflection survey by the BMR recorded 254 km of 8-fold CDPseismic data, along three seismic lines. Line BMR89.B01, 157 km in length, crossed major features including the Comet Ridge, Bowen Basin, Duaringa Basin and Gogango OverfoldedZone. Line BMR89.B02 was recorded as an easterly extension of Line BMR89.B01, positioned further north due to ease of access. Line BMR89.B03 was positioned to providea north-south line crossing inferred transfer faults of the geological corridor followed by LineBMR89.B01. One expanding spread consisting of 9 shots was recorded on Line BMR89.B01centred at SP 2025 with maximum offsets of 25.6 km. Gravity observations were made at 480 m intervals on all seismic lines.

No abstract available

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No abstract available