Australian Geological Survey Organisation Research Articles

Crustal architecture of central Australia based on deep seismic reflection profiling

The crustal architecture of central Australia is interpreted from deep seismic reflection profiling conducted by the Australian Geological Survey Organisation in two surveys in 1985 and 1993. The seismic traverses, oriented normal to the main surface structures, ran north-south in central Australia, and crossed parts of the Arunta Block, Amadeus Basin, Musgrave Block and Officer Basin. The present crustal fabric was set in place by the end of the Mesoproterozoic (by about 1100 Ma). Reactivation of the structures took place in a continental intraplate setting mainly during the Middle-Late Palaeozoic Alice Springs Orogeny, but also during other orogenic events. In the Arunta Block. the crust is dominated by major north-dipping planar structures, interpreted as thick-skinned thrusts. Many of these thrusts cut deep into the crust, and at least one, the Redbank Thrust Zone, appears to cut and offset the Moho. In contrast, in the northern Musgrave Block, limited field mapping and teleseismic data suggest that the major crustal-scale planar structures are south-dipping. In the central to southern Amadeus Basin, deformation is essentially thin-skinned, with north-directed thrusting confined to the sedimentary succession. Thus, the deep seismic profiles in central Australia show a present day crustal architecture that is the response of the crust to Mesoproterozoic terrane amalgamation and to later reactivation by intraplate deformational events. Therefore. central Australia is a model for intraplate cratonic deformation that occurs in continental crust that is cold. thick and strong.

NON-VOLATILE HYDROCARBON CHEMISTRY STUDIES AROUND A PRODUCTION PLATFORM ON AUSTRALIA'S NORTH WEST SHELF

In September 1994 and 1995, scientists from the Australian Institute of Marine Science (AIMS) and the Australian Geological Survey Organisation (AGSO) conducted surveys aboard the Research Vessel Lady Basten to determine the dispersion, fates and effects of Produced Formation Water (PFW) discharged from the Harriet A production platform near the Montebello Islands, on the North West Shelf of Australia. This report describes the non-volatile hydrocarbon chemistry studies.We measured the dispersion of the PFW into dissolved and particulate fractions of seawater using moored high volume water samplers, surface screen samplers and moored and drifting sediment traps. We studied bioaccumulation using transplanted oysters, and we measured dispersion into sediment with benthic grabs. Samples were analysed for total non-volatile hydrocarbons and individual hydrocarbon components using ultraviolet fluorescence spectroscopy (UVF), gas chromatography with flame ionisation detection (GC-FID), and GC with mass selective detection (GC/MS). The hydrocarbon concentrations were used to calculate vertical fluxes and the total concentrations of hydrocarbons in the various ecosystem compartments. A mass balance model was then used to calculate the rates of other important dispersion and degradation processes.We estimate the potential zone of biological impact in the water column extends to a distance of approximately 0.5 nmile (900 m). Concentrations of oil in sediments were too low to indicate potential toxicity. By the collaborative application of oceanographic and geochemical techniques to marine environmental problems, we endeavour to provide effective feedback to the oil industry to gauge the effectiveness of their operational strategies in minimising impact in these pristine regions.

TRACKING PRODUCED FORMATION WATER DISCHARGE FROM A PETROLEUM PRODUCTION PLATFORM TO THE NORTH WEST SHELF

During September 1995, the Australian Geological Survey Organisation and the Australian Institute of Marine Science took part in a joint survey to monitor the dispersion, fates and effects of Produced Formation Water (PFW) discharged from the Harriet A production platform. Continuous Geochemical Tracer(CGT) analysis of benzene, toluene and C1−C6 hydrocarbons was used to map the spatial distribution of the PFW discharge in near surface waters. Hydrographic parameters were also continuously measured and four hydrocarbon vertical profiles were completed at various distances from the platform.PFW collected at the Harriet A production platform contained 3.75 mg/L of C1−C6 hydrocarbons; 1.59 mg/L of benzene and 1.72 mg/L of toluene. Benzene, toluene and total C1−C6 hydrocarbons are sensitive tracers of PFW, with concentrations of benzene and toluene in the PFW plume about 100 fold higher than typical 'detectable background' levels. Maximum concentrations measured within the PFW discharge plume were 140 ng/L for benzene, 250 ng/L for toluene and 1500 ng/L C1−C6 hydrocarbons. Minimum dilutions of about 2,500 for C1−C6 hydrocarbons and less than 10,000+ for benzene and toluene were measured at distances 1 km from the platform. Thus, close to the platform, benzene and toluene are apparently more 'reactive' than C1−C6 hydrocarbons and disperse more rapidly.The PFW discharge was mapped in a NNW and SSE direction on both the ebb and flood tides to a maximum distance of 10 km from the production platform. A net westerly drift of the plume was evident on both the ebb and flood tides toward the Montebello Islands and Varanus Island, rather than toward the east and the mainland. A one dimensional dispersion model found hydrocarbons are dispersed in seawater, with characteristic half-dispersion distances of about 3.5 km on a spring tide. Vertical profiles of PFW hydrocarbons suggest that within 1 km of the platform the PFW plume is primarily a surface feature but beyond 1 km all hydrocarbons are well mixed.

Aeromagnetics locates prospective areasandprospects

The experience of the Australian Geological Survey Organisation (AGSO) is that properly acquired, processed, and interpreted aeromagnetic surveys can locate not just areas with hydrocarbon exploration potential but specific prospects in them. Furthermore, in many situations aeromagnetics provides important ancillary information that can be related to such important factors as migration and maturation.

Data Preparations for a new Australian Gravimetric Geoid

Abstract The rationale is given for a new determination of the Australian gravimetric geoid. In preparation for this task, the Australian Geological Survey Organisation’s gravity data base has been validated and reformatted. Additional information in the form of digital terrain data are available from the Australian Surveying and Land Information Group’s 9″ by 9″ Digital Elevation Model (DEM), derived from ∼5.2 million spot elevations and the ∼0.6 million elevations in the gravity data base. Both gravity and terrain data were transformed to give their horizontal position on the GRS80 ellipsoid, which produces a homogeneous data source for subsequent geoid computations. The gravity anomalies were computed using a second-order, free-air correction and normal gravity was computed using GRS80 latitude. Satellite altimeter-derived gravity anomalies are also considered as an additional source of information in offshore areas. The statistical fit of the new EGM96 global geopotential model to geometrical control ...

Compilation of geophysical signatures of South Australian mineral deposits: a progress report

To take advantage of large quantities of new geophysical data and increased exploration interest due to the South Australian Exploration Initiative a compilation of the geophysical signatures of South Australian mineral deposits has been undertaken. This project has two stages which will be described in a two-volume publication. The first volume, scheduled for publication in 1996, summarises all publicly available data, and some proprietary data, on the geophysical signatures of the State’s mineral deposits. Separate chapters describe deposits according to the dominant commodity. These include copper, iron, uranium, lead-zinc, and other commodities such as gold, nickel, talc and graphite. The total number of deposits discussed is 44.The second volume, scheduled for publication in early 1997, is primarily concerned with newly acquired airborne geophysical data, from the South Australian Exploration Initiative and also Australian Geological Survey Organisation and commercial surveys. The majority of the data described will be aeromagnetic, but other data will be included as required and available. For each deposit, data from the surrounding few tens of kilometres will be presented and interpreted with emphasis on lithological and structural control of the deposit. Regional-scale interpretations will also be included, again emphasising controls on known mineralisation.

Automated AF-demagnetization on the 2G-Enterprises through-bore, cryogenic magnetometer

Since the early sixties, alternating field demagnetization (AFD) has been a standard laboratory technique for demagnetizing rocks to expose the multicomponent structure of their natural remanent magnetization (NRM). In the majority of AFD implementations, however, the procedure remains as labour-intensive as ever. The implementation that we have developed at the Australian Geological Survey Organisation, automates the procedure for AFD based on the static method, and results in significant productivity and efficiency gains without compromising data quality. A properly formulated procedure for static AFD may be the only method of retrieving higher-coercivity components of natural remanence in samples prone to developing gyroremanence at higher alternating fields (AFs). Our AFD environment comprises: a 2G-Enterprises through-bore, cryogenic magnetometer; 2G AF-coils and control equipment; and personal computer software, developed by us, to control all procedural aspects for a complete AFD of a sample including, importantly, a counteracting procedure to neutralize the effects of gyroremanence build-up at higher AFs. With our system, AFD of 8 samples/day, each of 20+ steps, requires only 20 min of user attention compared with a full day for conventional systems.

Tectonic structure and petroleum potential of TayabasBay southeast Luzon, Philippines

Tayabas Bay is one of four offshore Philippine areas where the Australian GeologicalSurvey Organization and the Philippine Department of Energy conducted a cooperative marine seismic, gravity, magnetic, bathymetry and geochemical survey. The project acquired new seismic data and reprocessed the 1983 World Bank seismic sections which were all integrated with previous oil company data. the absence of wells drilled offshore, interpretation of offshore seismic data was complemented by onshore well log information and stratigraphy of the Bondoc Peninsula. Geochemistry data, both offshore and onshore, were analyzed to confirm the presence of mature source rocks and hydrocarbon migration. A new seismic interpretation has revealed the structure of this tectonically active geologically complex area. A major structural feature interpreted in offshore Tayabas Bay was a N-NW-trending strike-slip fault which is believed to be a northern splay of the Sibuyan Sea Fault. The authors named this fault the Tayabas Bay Fault and due to its association with the Philippine Fault System the movement is assumed to be left-lateral. The present study suggested the presence of a prolific source rock in the Middle Miocene Vigo Formation and/or the Late Oligocene to Early Miocene Panaon Limestone. Oil and gas generation have been and are occurring in the Bondoc Sub-basin. Two groups of reservoirs were identified, the shelf carbonates beneath the Middle Miocene shales on the Marinduque Platform and the early Middle Miocene carbonates and basin-floor clastics near the base of the Vigo Formation. Carbonate reservoirs are believed to be present in traps formed when the Late Oligocene to Early Miocene carbonate reefs and shelf deposits of the Panaon Limestone were buried by the Middle Miocene shales. A later set of traps was formed and possibly superimposed by the intense deformation associated with the Philippine Fault System which has continued from the Late Pliocene up to the present. Evaluation for hydrocarbon reserves of several possible traps identified three significant leads, namely the Yuni Lead in the south, the Mulanay in the central area and the Mabio in the North.

Petroleum Hydrogeology of the Cooper and Eromanga Basins, Australia: Some Insights from Mathematical Modeling and Fluid Inclusion Data

Mathematical modeling and fluid inclusion data analysis are used to reconstruct the petroleum hydrogeology of the Australian Cooper and Eromanga basins. Our analysis focuses on the development of topography- and compaction-driven groundwater flow systems and their role in heat redistribution, petroleum generation, and oil and brine migration during basin evolution. Finite-element models of basin transport processes are constructed along northeast-southwest (AA´) and northwest-southeast (BB´) cross sections that generally follow the present-day groundwater flow patterns through these basins. Numerical results are presented in the ©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.1Manuscript received September 19, 1995; revised manuscript received July 3, 1996; final acceptance November 11, 1996. 2Independent Consultant, 12 Rinzee Road, Dracut, Massachusetts 01826. 3CSIRO Division of Petroleum Exploration, 51 Delhi Road, North Ryde, NSW 2113, Australia. 4Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, Minnesota 55455 (E-mail: mperson@ darcy.geo.umn.edu) 5GZA GeoEnvironmental Inc., 380 Harvey Road, Manchester, New Hampshire 03103. 6Santos Ltd., 101 Grenfell Street, Adelaide, SA 7000, Australia. This research is supported by a grant from the Petroleum Research Fund, administered by the American Chemical Society, PRF 24184-AC8. We would also like to acknowledge the Orpha and George Gibson Hydrogeology Endowment and the McKnight Land-Grant Professorship Program at the University of Minnesota. We thank the CSIRO Division of Exploration Geosciences for providing support for travel costs within Australia. Data provided by Santos Ltd. and the Department of Mines and Energy, South Australia, are also gratefully acknowledged. Computational work performed on this project was done at the Gibson Computational Hydrogeology Laboratory at the University of Minnesota, which is supported by the National Science Foundation under EAR 94-05807. Special thanks go to M. A. Habermehl of the Australian Geological Survey Organization, David Gravestock of the South Australia Bureau of Mines and Mineral Resources, and Mike Congreves of Santos Ltd. for their assistance on interpreting the petroleum geology and hydrogeology of the Cooper and Eromanga basins. The review comments of Joseph Toth, Stefan Bachu, and Michelle Walvoord, as well as discussions with Ward Sanford, greatly improved the quality of this manuscript. Three-dimensional model results presented in this paper are available in animated form on VHS videocassette and can be obtained by contacting Mark Person at the address listed for him as the corresponding author.

A National Digital Elevation Model for Resource and Environmental Management

The third dimension, elevation, is a vital component of Australiais National Spatial Data Infrastructure. Elevation information in an easily accessible digital form is necessary for efficient and effective management of natural resources and the environment. Elevation is needed for analysis and modelling in areas as diverse as climate, biodiversity, salinisation, the rectification of satellite imagery, hydrology, telecommunications, infrastructure planning, and geology and geophysics. The need for such information on a regional and national basis has been the catalyst for the production of a national gridded digital elevation model using a cell spacing of 9 seconds of latitude and longitude. Production of the recently released GEODATA 9 SECOND DEM was undertaken by the Australian Surveying & Land Information Group, Australian Geological Survey Organisation, Australian Heritage Commission and the Centre for Resource and Environmental Studies at the Australian National University. This paper briefly examine...

Short-period geomagnetic variations recorded concurrently with an aeromagnetic survey across the Bendigo area, Victoria

A high-resolution aeromagnetic survey was undertaken by the Australian Geological Survey Organisation (AGSO) across the Bendigo 1:250 000 map sheet area during February to April 1994. For part of this period, high-resolution ground magnetometers were also deployed to test for the way that short-period variations of the geomagnetic field (including micropulsations) affect data recorded by the aircraft. These ground instruments consisted of the newly developed Helium base-station for AGSO aeromagnetic surveys, and two ring-core fluxgate magnetometers developed by the School of Earth Sciences at The Flinders University of South Australia. The Helium instrument was deployed at the Bendigo airport, in the south-west corner of the area, and the ring-core instruments were buried in the north-west and north-east corners of the area. Preliminary results indicate that while the phases of continuous Pc3 micropulsations of about 20 s period change little across the map sheet area, the amplitudes can vary significantly. For longer period geomagnetic variations (60 s to 600 s), there are significant differences in the amplitudes and phases of the total-field values measured at different sites. Induction vectors indicate a shallow zone of higher conductivity between the east and west measurement sites. Data from a single base-station magnetometer subtracted from airborne survey data will not adequately remove the short-period geomagnetic variations of the total field recorded during this survey period ? they are an additional noise source in the survey data.

Research cruise yields new details of Macquarie ridge complex

During a 44‐day expedition on board the Australian vessel Rig Seismic, scientists collected new information on the morphology of the Macquarie Ridge Complex (MRC), located at the boundary between the Pacific and Australian plates. In the joint venture, funded by the U.S. National Science Foundation and Australian Geological Survey Organization (AGSO), investigators from the two countries studied deformation in the area along the MRC, which includes the site of the largest earthquake of the 1980s (May 23, 1989, Mω=8.2).The researchers acquired ∼160,000 km2 of HAWAII MR1 (HIG acoustic wide‐angle imaging instrument, mapping researcher 1) side‐scan sonar/bathymetry images and ∼7000 km of 8‐channel seismic reflection data (Figure 1). In addition, three ∼400‐km gravity transects of the MRC were completed across the morphologic ridge and trench system. The transects were augmented by 96‐channel seismic reflection imaging across the morphologic ridge and trench system. Gravity and magnetic data were collected during the entire survey.

The Australian National Seismograph Network

The Australian Seismological Centre of the Australian Geological Survey Organisation, operates and co-operates a national seismograph network consisting of 24 analogue and 8 digitally telemetred (3 broadband) stations (see fig. 1 and table 1). The network covers the Australian continent and the Australian Antarctic Territory.

Review of recent results from continental deep seismic profiling in Australia

The Australian Geological Survey Organisation regularly collects 450–500 km of onshore deep seismic reflection data and up to 4500 km offshore each year in Australia. These recordings are made in a wide range of tectonic provinces, including, in the last few years, late Palaeozoic-Mesozoic intracontinental and Palaeozoic-Mesozoic-Cenozoic continental margin extensional basins, moderately deformed Palaeozoic transtensional basins and compressional fold belts, and Archaean greenstone terranes. Several of these provinces are major petroleum exploration provinces, whereas others contain significant mineral deposits. The primary purpose of the deep seismic profiling program is to resolve the tectonic history of the Australian continent, and thereby to encourage exploration for hydrocarbons and mineral resources in Australia. On the northwest Australian continental margin, major basin systems including the Bonaparte Basin, formed as a result of complex interactions since the Carboniferous, involving episodes of extension followed by strike-slip movements and inversion, which reactivated both the primary extensional and ancient basement structures. Off southeastern Australia, basins such as the Gippsland Basin formed as part of a linked transtensional system related to movement on a common mid-crustal detachment complex. On continental Australia, the Bowen Basin, in the northeast, was deformed by thrust faults that root in a major E-dipping detachment that flattens in the middle crust. The Cobar Basin, in the southeast, is a case where the seismic data support a detachment model in which the upper plate displacement vector can be calculated by plate reconstructions linking the geometry of the detachment surface with that of the basin. The greenstone terranes within the Eastern Goldfields region of Western Australia show crustal-scale fault systems that are planar and steep dipping, more in keeping with those interpreted in data from other Precambrian provinces rather than those of the Palaeozoic provinces.

Tests of Australian aerial radiometric data for use in petroleum reconnaissance

Recon Exploration Pty. Ltd. has successfully completed initial testing of a new method for processing and interpretation of AGSO’s (Australian Geological Survey Organization, formerly Bureau of Mineral Resources) aerial gamma‐ray spectrometer data for petroleum exploration in the Canning Basin, Western Australia and the Otway Basin, Victoria. Count‐rate data for potassium and uranium were normalized to the thorium count rate for each sample to suppress unwanted effects of variations in surface lithology or soil type, soil moisture, vegetation cover, and counting geometry. The Canning Basin test area included five producing oil fields. All except one clearly exhibit significant and characteristic radiometric anomalies which include negative normalized potassium and more positive normalized uranium values. The Otway Basin test areas included PPL-1 commercial gas production which is associated with a group of significant radiometric anomalies similar to those in the Canning Basin. These results are similar to extensive ongoing tests in the U.S. and are explained in terms of well‐understood geological, geochemical, and geophysical models. Based on 69 wells in the three test areas, it is estimated that the chance of encountering hydrocarbons (economic production or shows) in wells within the radiometrically favorable zones is about 2.6 times greater than outside the favorable areas.

PETROLEUM POTENTIAL OF RAGAY GULF, SOUTHEAST LUZON, PHILIPPINES

During March-May 1992, the Australian Geological Survey Organisation and the Philippine Department of Energy conducted a cooperative marine seismic and underway geochemical survey in four offshore Philippine basins which included Ragay Gulf. The project was funded and supported by the Australian International Development Assistance Bureau.The newly acquired and reprocessed seismic data from Ragay Gulf show a significant improvement in penetration and stratigraphic resolution. Seismic interpretation has revealed the existence of five sedimentary sub-basins with 2.5 – 6 seconds of Eocene to Recent sediments. Several potential traps have been evaluated for hydrocarbon reserves and new prospects are identified.No well has been drilled offshore in the Ragay Gulf. Onshore well log information and stratigraphy have assisted in the correlation and interpretation of offshore seismic data and allowed potential reservoirs to be recognised. The primary reservoir targets are the carbonate sequences of both Early and Late Miocene age. The widespread volcanoclastic sand may be an important secondary target, especially for gas reservoirs.Onshore and offshore geochemical data have confirmed the presence of mature source rocks from which generated hydrocarbons are currently migrating to the surface and, by inference, to reservoirs.A wide diversity of play types is recognised which could have been sourced from three separate source kitchens in the Bondoc, Ragay and Burlas Sub-basins. Specific entrapment possibilities are:Compressional fault-dependent traps (e.g. Anima Sola).Compressional anticlinal fault independent traps (e.g. Alibijaban and Palad).Late Miocene carbonate reefal buildups (e.g. Apud and Gorda).Early Miocene carbonate reservoirs in drape over highs (e.g. San Narciso and Bagulaya).

A preliminary result of the Ragay Gulf survey in the Philippines

During March-May 1992, the Australian Geological Survey Organisation and the Philippine Office of Energy Affairs conducted a cooperative marine seismic, gravity, magnetic, bathymetry and geochemical sniffer survey in four offshore Philippine basins: NE Palawan, Cuyo Platform, Tayabas Bay and Ragay Gulf. The project was funded by the Australian International Development Assistance Bureau. The survey work was conducted using the Australian Government's geoscientific vessel, Rig Seismic. The cruise achieved all its objectives and was a major success. Of the four survey areas, the Ragay Gulf is of particular interest, with complex structures, multi-phase tectonism and massive sediment infill. It was in this region that many geochemical sniffer seeps were located. The geochemical sniffer data and its C-13 and C-14 isotope analyses have indicated the presence of significant source rocks. These seeps are thermogenic in origin and have reached sufficient maturity to generate significant quantities of hydrocarbons. In the near future, the geochemical data will be integrated with the seismic data to provide clues for hydrocarbon migration. The preliminary seismic interpretation have revealed the existence of five sedimentary sub-basins with 2.5 - 5 seconds of Eocene to Recent sediments. Several types of potential traps were documented. No well has been drilled in the offshore Ragay Gulf. Onshore well log information and stratigraphy have assisted in the correlation and interpretation of offshore seismic data. In addition, the importance of the carbonate and clastic reservoirs was recognised. Overall, the oil and gas potential in the Ragay Gulf area looks most encouraging.

On the Gravity Signature of Archaean Greenstones in the Widgiemooltha-Tramways Area, Eastern Goldfields, Western Australia

A detailed gravity traverse is described along the Western Mining Corporation ? Australian Geological Survey Organisation (WMC-AGSO) Widgiemooltha-Tramways crustal seismic profile. Positive Bouguer anomalies of up to 20 mGal over the greenstone sequence imply that up to 3.5 km of mafic stratigraphy occur along the profile. Comparisons to the seismic data imply the presence of a felsic stratigraphic unit forming the base of the supracrustal greenstone succession. The 3-D structure of local successor basins (Black Flags and Merougil Beds) above the mafic stratigraphy are also constrained by the gravity data to a maximum vertical thickness in the order of 3 km. The Widgiemooltha granodiorite is modelled by the seismic and gravity data as a steep-sided intrusion underlain at depth (~ 3 km) by felsic greenstone stratigraphy.

The Repeat Station Network and Estimation of Secular Variation in the Australian Region

The repeat station network run by the Australian Geological Survey Organisation is a cost-effective way of supplementing data from the permanent magnetic observatories for the estimation of secular variation in the Australian region.

COALBED METHANE RESOURCES IN THE PERMIAN OF EASTERN AUSTRALIA AND THEIR TECTONIC SETTING

The Bowen and Sydney Basins in eastern Australia contain vast coal resources which provide a source for coalbed methane. Through studies of the spatial and temporal distribution of the sedimentary packages, the structural geometry and tectonic setting of the sedimentary packages, and the maturation and burial history, the Australian Geological Survey Organisation (AGSO) is mapping the distribution and structural styles of the sources of methane, in particular, the Late Permian coal measures. AGSO's results from the Bowen Basin show at least two distinctly different structural styles of potential targets for coalbed methane drainage: on the Comet Ridge, the Permian coal measures are essentially subhorizontal and tectonically undisturbed, whereas in the western Taroom Trough, the coal measures are folded into a series of anticlines, each of which occurs above a thrust fault which in turn forms part of an imbricate thrust fan. Both of these styles occur at depths of less than 1000 m.Calculations by the Bureau of Resource Sciences (BRS) indicate that the inferred coalbed methane resources-in-place are 62 trillion cubic feet (1760 billion m3) for Australia, in which the Bowen and Sydney Basins are currently the only potential provinces of coalbed methane. The low permeability of the coal seams hinders attempts to utilise this vast amount of energy resources.Further exploration is necessary to delineate commercially feasible areas. This delineation is the only process that will be able to determine demonstrated coalbed methane resources.