Australian Geological Survey Organisation Research Articles

New insights on Upper Cretaceous stratigraphy and sedimentology of the Bight Basin, Australia from IODP Site U1512

The Bight Basin, on Australia’s southern margin, is one of the world's most prospective deepwater frontier basins. The 10 offshore wells drilled in the basin had limited success or yielded disappointing results. There has been a strong dependence on seismic data to interpret stratal ages and the regional depositional history because of the limited number of wells, which are all in the more proximal region. In October 2017, the International Ocean Discovery Program Expedition 369 drilled a hole at Site U1512 that straddled the Australian Geological Survey Organisation Survey s065 line 06 on the continental slope, ~67 km south-east of the Jerboa 1 well. The recovered core is the most extensive lithological dataset acquired from the basin and consists of a 10 m thick Pleistocene ooze overlying a 690 m succession of Turonian–Santonian strata. The Cretaceous strata consist of silty claystone with a few thin beds of glauconitic and sideritic sandstone (<32 cm thick). The Tiger Supersequence is substantially thicker than had been anticipated. Preliminary palynofacies analysis indicates a prevailing dysoxic marine environment, with the assemblage dominated by phytoclasts (40–90% of the assemblage). This may have been a consequence of high rates of freshwater runoff into the restricted basin. Rapid sedimentation rates (up to 260 m/Myr), the silt content (2–25%) and the palynofacies suggest the strata were deposited primarily by hyperpycnal and hypopycnal flows. These new datasets will provide a means to re-evaluate the palaeogeography of the basin and its resource potential.

Radiometric survey in geological mapping of basement complex area of parts of Southwestern Nigeria

Radiometric methods were used to investigate the radioactive properties of rocks in parts of southwestern Nigeria with a view to interpreting the geological structure and abundance of natural radioactive elements in the main type rocks. The airborne radiometric dataset of Ikole Sheet and ground radiometric data recorded from eight traverses in Akoko axis of the study area were processed. Results presented as maps and profiles displayed variations of high and low radioactive concentrations across the area. These maps showed moderate to very high concentrations and very low to low concentrations of the radioelements; uranium (4.5-13.0 ppm); (LLD-low limit of detection -3.0 ppm), Th (25.0-70.0 ppm); (8.5-16.0 ppm) and K (2.0-4.0 %); but the most often observed values are in the range 2.5-7.0 ppm, 22.0-30.0 ppm and 3.0-4.0% for U, Th, and K respectively. High concentrations imply that the rocks are crystalline, undeformed and are rich in feldspar and U-Th bearing minerals. While low radioactivity is attributed to varying geologic framework compositions; weathered materials or fluids formed as a result of intense metamorphism. The radiometric datasets proved valuable in delineating different rock types and serve as a complementary tool in identifying geochemical zoning of rocks in the area.ReferencesAjibade A.C. and Fitches W.R., 1988. The Nigerian Precambrian and the Pan-African Orogeny, Precambrian Geology of Nigeria, 45-53.Ajibade A.C., Woakes M. and Rahaman M.A., 1987.Proterozoic crustal development in Pan-African regime of Nigeria: In A. Croner (ed.) Proterozoic Lithospheric Evolution Geodynamics, 17, 259-231.Appleton J.D., Miles J.C.H., Green B.M.R, Larmour R., 2008. Pilot study of the application of Tellus airborne radiometric and soil geochemical data for radon mapping. Journal of Environmental Radioactivity, 99, 1687-1697.Arisekola T.M. and Ajenipa R.A., 2013. Geophysical data results preliminary application to uranium and thorium exploration. IAEA-CYTED-UNECE Workshop on UNFC-2009 at Santiago, Chile 9-12, July, 12.Bayowa O.G., Olorunfemi O.M., Akinluyi O.F. and Ademilua O.L., 2014.A Preliminary Approach to Groundwater Potential Appraisal of Ekiti State, Southwestern Nigeria. International Journal of Science and Technology (IJST), 4(3), 48-58.Bierwirth P.N., 1997. The use of airborne gamma-emission data for detecting soil properties.Proceedings of the Third International Airborne Remote Sensing Conference and Exhibition.Copenhagen, Denmark.Grasty R.L. and Multala J., 1991. A correlation technique for separating natural and man-made airborne gamma-ray spectra. In: Current Research, Part D, Geological Survey of Canada, 111-116.Grasty R.L., Minty B.R.S., 1995a. A guide to the technical specifications for airborne gamma ray surveys. Australian Geological Survey Organization, Record.Grasty R.L., Minty B.R.S., 1995b. The standardization of airborne gamma-ray surveys in Australia. Exploration Geophysics, 26, 276-283.IAEA, 1991. Airborne gamma ray spectrometer surveying, International Atomic Energy Agency, Technical Report Series, 323.IAEA, 2007.International Atomic Energy Agency. Safety Glossary, Terminology used in Nuclear Safety and Radiation Protection-2007 Edition.Jones H.A. and Hockey, 1964.The Geology of part of’ Southwestern Nigeria.Geological Survey, Nigeria bulletin, 31.Kearey P., Brooks M. and Hill I., 2002. An Introduction to Geophysical Exploration.3rd ed. Oxford: Blackwell Science, 262.Milsom J., 2003. Field Geophysics: The geological field guide series, John Milsom University College, London. Published by John Wiley and Sons Ltd. Third edition, 51-70.MontajTM Tutorial, 2004. Two - Dimensional frequency domain processing of potential field data.Nigeria Geological Survey Agency (NGSA), 2009. Geological map of Nigeria prepared by Nigeria Geological Survey Agency, 31, ShetimaMangono Crescent Utako District, Garki, Abuja, Nigeria.Omosanya K.O., Ariyo S.O., Kaigama U., Mosuro G.O., and Laniyan T.A., 2015. An outcrop evidence for polycyclic orogenies in the basement complex of Southwestern Nigeria. Journal of Geography and Geology, 7(3), 24-34.Oyawoye, M.O., 1972. The Basement Complex of Nigeria.In African Geology. T.F.J. Dessauvagie and A.J. Whiteman (Eds) Ibadan University Press, 67-99.Oyinloye A.O., 2011. Geology and Geotectonic Setting of the Basement Complex Rocks in Southwestern Nigeria: Implications on Provenance and Evolution. Earth and Environmental Sciences, 98-117. ISBN: 978-953-307-468-9.Rahaman M.A., 1981. Recent Advances in the Study of the Basement Complex of Nigeria.First Symposium on the Precambrian Geology of Nigeria, Summary.Rahaman M.A., Emofureta W.O. and Vachette M., 1983. The potassic-grades of the Igbeti area: Further evaluation of the polycyclic evolution of the Pan-African Belt in South-western Nigeria. Precambrian Resources, 22, 75-92.Woakes M., Rahaman M.A., Ajibade A.C., 1987. Some Metallogenetic Features of the Nigerian Basement. Journal of African Earth Sciences, 6(5), 655-664.

Customising the geological timescale for use in Australasia

The global standard geological timescale (GTS 2004) is largely built around northern hemisphere datasets. Consequently, a large proportion of the biozones used in Australia were not included, thus hampering its implementation in the region. Previously, most of the Australasian biozonal schemes had been tied to the Australian Geological Survey Organisation timescale (AGSO 1996) but each of these needed to be recalibrated to tie with the updated and globally standardised GTS 2004. This process was complicated by the fact that several of the local biozonal schemes have been revised in the intervening period. The updates of Australian biozones to GTS 2004 compliance were accomplished using extensive literature searches as well as targetted reviews of some biozonal schemes. These recalibrated and amended schemes have now been included in Geoscience Australia’s Timescales Database, which acts as a core lookup table for numerous databases across the organisation. In 2010, GTS 2004 will be replaced by an updated standard timescale. To facilitate this transition and other future revisions, Geoscience Australia’s Timescales Database is being revised to store the relationships between biozones and the geological timescale in a format that will allow essentially automatic, rather than protracted manual, updates. A public visualisation software package, Time Scale Creator, is available on the web from the International Commission on Stratigraphy (ICS) to display user-selected intervals from an ICS database suite of over 20,000 biological, geomagnetic, sea-level, and other events with ages consistent with GTS 2004. Geoscience Australia (GA) has compiled a customised datapack for Time Scale Creator which includes most Australian biozonal schemes. In addition, Geoscience Australia is using the lithostratigraphic capabilities of this software package to generate basin biozonation and stratigraphy charts, which supersede those published nearly a decade ago.

A Special Issue Devoted to the Early to Middle Archean Mineral Deposits ofthe North Pilbara Terrain, Western Australia

The Archean eon is a highly mineralized eon in geological time, producing a significant proportion of the world’s Au, Cu, Zn, and Ni. However, much of this mineralization is concentrated within the period from 2740 to 2620 Ma, a time characterized by extensive crustal growth and mineralization and referred to by Barley et al. (1998) as the Archean Numerous papers have been written about Late Archean mineral deposits and their tectonic environments, yet this Late Archean bonanza comprises only 120 m.y. of an eon that spanned from 4000 to 2500 Ma. By comparison, the period prior to the Late Archean bonanza is poorly mineralized and its metallogenesis has not been as comprehensively described, in part because few rocks of this age have been preserved. To understand the evolution of mineralizing processes through time, however, it is essential to document the characteristics of mineral deposits and their environments during the Early to Middle Archean, as well as in the Late Archean bonanza. The North Pilbara terrain (previously known as the Pilbara block) of Western Australia is one of the best preserved regions of Early to Middle Archean crust on Earth and as such offers an ideal opportunity to record mineralizing processes prior to the Late Archean. In 1995, Geoscience Australia (then the Australian Geological Survey Organisation) joined with the Geological Survey of Western Australia in the North Pilbara National Geoscience Mapping Accord project to document the geology …

Geological Sequestration of Carbon Dioxide

John Bradshaw is Project Manager of Project 1 (Regional Analysis) in the GEODISC research project at the Australian Petroleum Cooperative Research Centre. He has a B.Sc. (Honours) and Ph.D. in Applied Geology from the University of New South Wales. John is an exploration technologist, with a regional knowledge of Australian sedimentary basins, and is employed as a Principal Research Scientist at the Australian Geological Survey Organisation. He has also worked for Esso (Australia) and on staff exchange for a year with WMC Petroleum and Ampolex/Mobil. He has extensive fieldwork experience throughout central Australia and Papua New Guinea, where he consulted for several years. John has previously run major industry-funded research projects examining the petroleum systems of Australia. He is a member of GSA, PESA, and AAPG. Peter Cook is currently Executive Director of the Australian Petroleum Cooperative Research Centre (APCRC) and a director of various companies. Previous positions include Senior Research Fellow (Australian National University), Division Chief-Associate Director (Australian Geological Survey), and Director of the British Geological Survey (1990–1998). It was during his time as Director of BGS that he became interested in the issue of geological sequestration of CO2, and on his return to Australia he established the GEODISC program of the APCRC. He has acted as an adviser to government organizations and companies in Europe, Asia, Australia, and North America, and he has held academic positions in Australia, the United States, France, and the United Kingdom. Peter Cook holds degrees in geology from the United Kingdom, Australia, and the United States. His research career has included studies of the sedimentology, geochemistry, and economic geology of ancient and modern environments in both inland and coastal parts of Australia and the evolution of Australia over the past 500 million years. He was leader of a major UNESCO program …

Long‐Term Landscape Evolution of the Northparkes Region of the Lachlan Fold Belt, Australia: Constraints from Fission Track and Paleomagnetic Data: A Reply

Previous articleNext article No AccessLong‐Term Landscape Evolution of the Northparkes Region of the Lachlan Fold Belt, Australia: Constraints from Fission Track and Paleomagnetic Data: A ReplyPaul B. O'Sullivan, Brad Pillans, David L. Gibson, Barry P. Kohn, and Colin F. PainPaul B. O'SullivanAustralian Geodynamics Cooperative Research Centre, School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia1Current address: 204 Heroy Geology Laboratory, Syracuse University, Syracuse, New York 13244‐1070, U.S.A.; e‐mail: [email protected] Search for more articles by this author , Brad PillansAustralian Geodynamics Cooperative Research Centre, School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia2Cooperative Research Centre for Landscape Evolution and Mineral Exploration, Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory 0200, Australia. Search for more articles by this author , David L. GibsonAustralian Geodynamics Cooperative Research Centre, School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia3Cooperative Research Centre for Landscape Evolution and Mineral Exploration, Australian Geological Survey Organisation, P.O. Box 378, Canberra, Australian Capital Territory 2601, Australia. Search for more articles by this author , Barry P. KohnAustralian Geodynamics Cooperative Research Centre, School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia Search for more articles by this author , and Colin F. PainAustralian Geodynamics Cooperative Research Centre, School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia3Cooperative Research Centre for Landscape Evolution and Mineral Exploration, Australian Geological Survey Organisation, P.O. Box 378, Canberra, Australian Capital Territory 2601, Australia. Search for more articles by this author Australian Geodynamics Cooperative Research Centre, School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, AustraliaPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 108, Number 6November 2000 Article DOIhttps://doi.org/10.1086/317957 Views: 10Total views on this site Citations: 1Citations are reported from Crossref HistoryReceived June 23, 2000 © 2000 by The University of Chicago. All rights reserved. PDF download Crossref reports the following articles citing this article:Paul Green, Ian Duddy, Peter Japsen Episodic kilometre-scale burial and exhumation and the importance of missing section, Earth-Science Reviews 553 (Oct 2022): 104226.https://doi.org/10.1016/j.earscirev.2022.104226

Acoustic Structure and Seismic Velocities in the Carnarvon Basin, Australian North West Shelf: Towards an Integrated Study

High quality refraction and wide-angle reflection seismic data recorded by ocean-bottom seismographs (OBSs) deployed by the Australian Geological Survey Organisation along the 700 km long transect in the Carnarvon Basin effectively supplement results obtained by means of the conventional reflection technology. Velocity information can now be derived from both CDP (nearvertical reflection) and OBS (refraction/wide-angle reflection) data. Generally, CDP-derived average velocities are lower than OBS-derived velocities and this deviation increases with depth: from ~0.1 km/s at 8 s two way time (TWT) to 0.8-1.6 km/s at 16 s TWT. If the CDP-derived velocities are used to depth convert reflection data, then depth to these TWTs would be underestimated by 0.4 to 6.4-12.8 km respectively. Some local anomalies (at ~6s TWT CDP-derived velocities may be more than 0.1 km/s higher than the OBS-derived velocities) distort this general trend. These would result in ~0.3 km local overestimates of the depth equivalent of 6s TWT. Co-analysis of the interval velocity field reconstructed from the travel time-based interpretation of the OBS data and the conventional reflection image of the crust in some cases shows their poor correlation. Prominent reflectivity seen in the conventional reflection data at depth 13-17 km does not correspond to any significant velocity increase imaged by refraction/wide-angle techniques. These reflections were taken in our pre-OBS interpretation to mark the top of the underplated layer in the crust. Velocity below that level estimated from the OBS data is in the range 5.7-6.4 km/s. This velocity range is considerably lower than anticipated for mafic rocks under appropriate PTconditions. Quite significant local velocity increase in the depth range 15-23 km does not produce high-amplitude near-vertical reflections. Only a combination of reflection and refraction/wideangle techniques provides a clue to a consistent geological interpretation of seismic data. Improved velocity estimation in the crust is crucial for accurate depth conversion of near-vertical reflection data.

THE EVALUATION OF THE GEOLOGIC MAPPING ACTIVITIES AND THE MANAGEMENT OF THE GEOLOGICAL SURVEY ORGANIZATIONS

Evaluation programs of research institutions began to be established in Europe in the late 70's, concerning the assessment of science and technology activity. In the geoscientific world this enterprise took place in the 1990's, with the implementation of evaluation processes in some national geological surveys (Australian Geological Survey Organization, Geological Survey of Canada, Council for Geoscience - South Africa, Geological Survey of Finland). Among the results of these evaluation/review processes it has been common to recommend the establishment or strengthening of Advisory Councils or Advisory Committees, made up of representatives from industry, academia and governmental agencies. On the trail of the Geological Surveys evaluation process, partnership national geological mapping programs with regional geological surveys, having customers, universities and industry representatives as advisory has also been stimulated. The National Geoscience Mapping Accord in Australia (1990), the National Geoscience Mapping Program in Canada (1991), and National Cooperative Geological Mapping Program in United States (1992) are examples of the government policies in wake of evaluation process. Nevertheless, it is important to say that institutional staff has not accepted evaluation with tranquillity or understood it as an instrument of management. This recent trend of management - making a connection to the customers/users/stakeholders - has been introduced into the Geological Surveys by initiative of government or agencies at high level hierarchy, i. e., from top to bottom, from outside to inside the corporation.

The evaluation of the geologic mapping activities and the management of the geological survey organizations

Evaluation programs of research institutions began to be established in Europe in the late 70's, concerning the assessment of science and technology activity. In the geoscientific world this enterprise took place in the 1990's, with the implementation of evaluation processes in some national geological surveys (Australian Geological Survey Organization, Geological Survey of Canada, Council for Geoscience - South Africa, Geological Survey of Finland). Among the results of these evaluation/review processes it has been common to recommend the establishment or strengthening of Advisory Councils or Advisory Committees, made up of representatives from industry, academia and governmental agencies. On the trail of the Geological Surveys evaluation process, partnership national geological mapping programs with regional geological surveys, having customers, universities and industry representatives as advisory has also been stimulated. The National Geoscience Mapping Accord in Australia (1990), the National Geoscience Mapping Program in Canada (1991), and National Cooperative Geological Mapping Program in United States (1992) are examples of the government policies in wake of evaluation process. Nevertheless, it is important to say that institutional staff has not accepted evaluation with tranquillity or understood it as an instrument of management. This recent trend of management - making a connection to the customers/users/stakeholders - has been introduced into the Geological Surveys by initiative of government or agencies at high level hierarchy, i. e., from top to bottom, from outside to inside the corporation.

Palaeochannels near West Wyalong, New South Wales: A case study in delineation and modelling using aeromagnetics

In November 1998, the Australian Geological Survey Organisation (AGSO) and the New South Wales Department of Mineral Resources acquired high-resolution airborne magnetic and gamma-ray spectrometric data along lines spaced 50 m apart and 60 m above ground level north of West Wyalong, New South Wales. In addition,AGSO post-processed a proprietary dataset of similarly high-resolution from an area immediately to the south, between West Wyalong and Temora, along the Gilmore Fault Zone. Anomalies interpreted to be caused by palaeochannel deposits have been identified in these datasets. Modelling of the airborne magnetic data was used to define the geometry of the palaeochannel deposits. These models were constrained using data from drill holes and downhole magnetic susceptibility measurements.Mapping palaeochannel deposits is of potential significance for mineral exploration and land and water research. Historically, alluvial gold, often palaeochannel-hosted, has accounted for a large proportion of Australia’s gold production. The study area is part of the historic Wyalong Goldfield and is part of the Bland Creek palaeovalley. Palaeochannel deposits may also be reservoirs of saline groundwater, and therefore are important in developing hydrogeological models for dryland salinity hazard assessment.Due to their depth of burial (often concealed beneath surficial sediments, to depths of 150 m), the palaeochannel deposits in the study area are mappable using either airborne magnetic or electromagnetic data, but not using gamma-ray spectrometry. The palaeochannel deposits contain detrital ferruginous maghaemitic pisoliths (which have extremely high magnetic susceptibility) concentrated in lenses in sand and clay.The resolution of the aeromagnetic datasets is compared with results obtained from surveys with different acquisition parameters. These tests suggest that an airborne geophysical survey flown with line spacing of less than 100 m can reveal important information about regolith materials, including channel-fill deposits such as in the sedimentary fill of the Bland Creek palaeovalley.

Crustal structure across the Vulcan Sub-basin from seismic refraction and gravity data

The attenuated continental crust between the Kimberley Block and the Timor Trough hosts some of the major oil and gas fields in Western Australia. The crustal structure has been interpreted from wide-angle seismic data acquired by the Australian Geological Survey Organisation during 1995/96. Ten ocean-bottom seismometers were deployed along a deep seismic reflection profile aligning NW with exploration wells Fagin and Crane. Data were recorded to offsets of 300 km. A total profile 335 km long and 48 km deep has been developed, by ray-tracing and inversion modelling of the refraction data, and verified by modelling gravity data. The model differentiates 7 crustal and 2 upper mantle layers. The crustal thickness varies between 25 to 30 km, being greatest beneath the Kimberley Block and Vulcan Sub-basin. The velocities within the upper mantle are ~8.1 km/s, while in the lower crust they vary from 5.9-6.2 km/s beneath the Kimberley Block, to 6.4-7.0 km/s elsewhere. Mid-crustal velocities are 5.5-6.2 km/s and 2.0-5.0 km/s in the overlying sedimentary section. Significant lateral variations exist in the lower crust and can be used to infer the limit of the Kimberley Block. A prominent reflector at 6s twt, which is widespread in the region, is not a significant velocity discontinuity. The Moho is not seen on the reflection records, but is a prominent feature in the refraction data. Iso-velocity lines do not necessarily coincide with reflection boundaries, possibly due to decreasing porosity with depth, especially beneath the Cartier Trough.

Seismic velocities in the North West Shelf Region, Australia, From Near-vertical and Wide-angle Reflection and Refraction Studies

A significant limitation of conventional seismic reflection technology is that it poorly constrains seismic velocities in the deep part of the section. These velocities are needed for seismic migration, to convert from time to depth, and to estimate the likely rock composition at depth. Seismic observations at large offsets can compensate for this limitation. The Australian Geological Survey Organisation recorded high-quality refraction and wide-angle reflection seismic data using ocean-bottom seismographs (OBS) along 5 profiles on Australia’s North West Shelf, to maximum offsets of 300 km. The OBS transects coincide with previously acquired deep-crustal seismic-reflection profiles. Consequently, velocity information can now be derived from two independent data sets: common-depth point (near-vertical) reflection data and refraction/wide-angle reflection data. Residual (difference between these two velocity data sets) velocity images can be produced and analysed. Even within the top 5 km of the section residuals between the OBS- and CDP-derived interval velocities vary from -0.5 to +3.5 km/s and increase further with depth. Consequently, the depth equivalent of 4 s two-way time will vary by up to 1.2 km or 10%. The practical implications of co-processing of seismic velocity information are: improved seismic velocity estimation, more accurate depth migration and depth conversion of seismic data and less distortion of amplitudes and shapes of geological structures after depth conversion.

USING INTEGRATED REMOTE SENSING TECHNOLOGIES TO EVALUATE AND CHARACTERISE HYDROCARBON MIGRATION AND CHARGE CHARACTERISTICS ON THE YAMPI SHELF, NORTHWESTERN AUSTRALIA: A METHODOLOGICAL STUDY

As part of a major interpretative study of the Yampi Shelf, northeastern Browse Basin, the Australian Geological Survey Organisation (AGSO) acquired regional seismic, water column geochemical sniffer (WaSi), RadarSat Synthetic Aperture Radar (SAR), and high resolution bathymetric data over the area between 1995 and 1998. These data have been integrated in order to better understand both the hydrocarbon charge and top seal capacity characteristics of the area, and the relative responses of assorted remote sensing technologies to hydrocarbon migration, leakage and seepage. The area investigated comprises part of a Palaeozoic to Mesozoic flexural ramp margin, which dips northwest away from the flanking cratonic Kimberley Block. The basement has a rugose topography, with some horst blocks elevated 500 m above the surrounding basement. Progressive onlap of Cretaceous post-rift seals onto the ramp causes the regional seal to become thinner and sandier margin- ward. In some of these more margin-ward locations, some prominent basement highs are 'bald' of seal, whereas in others, the seal thins dramatically onto topographically prominent, landward-dipping tilt blocks. Natural hydrocarbon seepage was confirmed independently by SAR and WaSi, though the relative response and sensitivity of each technology to seepage of varying rates and compositions are quite different. Overall, the principal seeping hydrocarbon is dry (

Seismic microzonation in Australia

Since the 1980s seismic microzonation studies have been undertaken in Australia to assess the likely effects of earthquakes on urban centres built on unconsolidated sediments. Presently the Nakamura method is used for processing data. So far parts of Perth, Adelaide, Cairns, Gladstone, Rockhampton, Newcastle, Sydney and Launceston have been zoned. The Launceston, Tasmania, study was the pilot study for many of these as it refined the methodology used and the data obtained were incorporated into a GIS database. Building heights and site factor zoning maps were produced for the Launceston City Council. One of the major activities, of the new initiative by the Australian Geological Survey Organisation (AGSO), popularly known as the ‘Cities Project’, is coordinating seismic microzonation throughout Australia. Microzonation data have been included in AGSO’s geohazards GIS database. This is helping local councils zone land for seismic hazards. State Emergency Services use the information to plan for emergencies resulting from the effects of earthquakes. These practical applications of seismic microzonation data will help mitigate the destructive effects of any future large earthquakes occurring near major urban centres. In the Launceston case it was found that there is a variable risk dependant on epicentral distance and the nature of relatively unconsolidated sediments in various parts of the city. Disastrous amplification could occur at some sites.

Non-volatile Hydrocarbon Chemistry Studies Around a Production Platform on Australia's Northwest Shelf

In September 1994 and 1995, scientists from the Australian Institute of Marine Science (AIMS) and the Australian Geological Survey Organization (AGSO) conducted surveys aboard the RV Lady Basten to determine the dispersion, fates and effects of produced formation water (PFW) discharged from the ‘Harriet A’ oil production platform near the Montebello Islands. This report is one of four related papers and describes the non-volatile hydrocarbon chemistry studies. The dispersion of the PFW into dissolved and particulate fractions of seawater were measured using moored high volume water samplers, surface screen samplers and moored and drifting sediment traps. Bio-accumulation was studied using transplanted oysters, and dispersion measured into sediment with benthic grabs.Results showed enrichment in non-volatile hydrocarbons in surface microlayer samples to a distance of 1·8km in the direction of tidal flow. Concentrations in surface microlayers near the platform varied by an order of magnitude and corresponded to when a surface slick was visible or not visible. Concentrations of oil in seawater ranged from 2·0 to 8·5μg l−1at near stations to 1·3μg l−1at 1·8km. Water column samples showed the processes of desorption from particles for soluble components occur within the range of 1·8km. Most particulate hydrocarbons drop out of suspension within c. 1 to 2km from the platform. Fluxes of particulate hydrocarbons through the water column at c. 1km, as estimated by moored sediment traps in 1995, were 138 to 148ng cm−2day−1. A decrease in sediment concentrations within c.1km of the platform was measured as 2·45±1·29μg g−1dry wt (n=15) in 1994 to 0·86±0·54μg g−1dry wt (n=21) in 1995, after the platform installed a centrifugal separator in the discharge treatment process. Thus the residence time of this relatively low molecular weight oil was estimated in the coarse aerobic sands surrounding the platform to be less than one year. Oysters suspended near the platform bio-accumulated hydrocarbons and other lipophilic organics in their tissues. Uptake rates and bio-concentration factors of hydrocarbons indicated potential toxicity at the near-field stations within c.1km radius.A mass balance was constructed to show the partitioning of the input of hydrocarbons from the PFW into the surrounding marine ecosystem. The rates of dissipation processes were estimated as follows: dilution from tidal currents>degradation in the water column>sedimentation>evaporation. The calculations based on maximum concentrations measured in the environmental samples accounted for 85% of the daily input suspended within a 1km radius.It is estimated that the potential zone of toxic influence in the water column extends to a distance of approximately 1km. 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 minimizing impact in these pristine regions.

Terrain correcting Australian gravity observations using the national digital elevation model and the fast Fourier transform

The release of a digital elevation model (DEM) for Australia on a 9″ (∼250 m) grid has enabled the computation of gravimetric terrain corrections thus allowing the computation of complete Bouguer anomalies across the continent. The terrain correction was calculated through a two‐dimensional fast Fourier transform algorithm applied to a linear, planar approximation of the terrain‐correction formula, and with a constant topographic density of 2670 kg.m‐3. The technique was applied to two datasets in order to test for instabilities in the terrain‐correction algorithm: the original 9″ DEM, and a 27″ DEM averaged from the 9″ data. The 27″ terrain corrections were compared with values supplied by the Australian Geological Survey Organisation in Tasmania: 86% of these data were found to agree within 3.91 μm.s‐2; 98% agreed to within 5.32 μm.s‐2 (1σ).

Multinational seismic investigation focuses on Rabaul volcano

An improved disaster‐reduction strategy for civil authorities and communities on the Gazelle Peninsula in Papua New Guinea is anticipated as a result of a multinational seismic investigation now under way there. Data collection has been completed but interpretation is at a preliminary stage. Volcanic eruptions in 1994 devastated the town of Rabaul and other communities on the peninsula.The investigation, known as the Rabaul Earthquake Location and Caldera Structure (RELACS) program, is building a seismic tomography image of the Rabaul volcano that will improve the precision with which volcano‐related earthquakes can be located in real time. This will enable the Rabaul Volcanological Observatory (RVO) to interpret seismicity patterns in detail and provide better advice to civil authorities. Among other things, the scientific analytical capacity of RVO will be upgraded by improving knowledge about the subsurface structure of the caldera. Conducting the work are scientists from the Australian Geological Survey Organisation (AGSO), the Australian National University (ANU), the University of Hokkaido in Japan, and the University of Wisconsin (UW) in the United States.

Australian geologists left reeling by budget cuts⃛

The Australian Geological Survey Organisation (AGSO) is to lose one-fifth of its funding and staff numbers as a result of budget cuts announced after the 1999-2000 budget earlier this month.

Radiometric evidence for Middle Devonian inversion of the Hill End Trough, northeast Lachlan Fold Belt

The publication of a new geological time‐scale by the Australian Geological Survey Organisation and radiometric dates from the Hill End goldfield have prompted the re‐examination of the timing of deformation of the Hill End Trough to determine whether it occurred in Middle Devonian or Early Carboniferous time. Palaeontological evidence from the western trough margin and the Capertee High dates the end of deposition in the trough as late Emsian or early Eifelian (385–382 Ma). After a mid‐Devonian hiatus of at least 15 million years, paralic sedimentation commenced on the Molong and Capertee Highs in late Frasnian or early Famennian time (367–363 Ma). No Upper Devonian sedimentary formations occur in the Hill End Trough. Structural relationships indicate that the oldest mineral veins at Hill End preceded cleavage formation in the deformed trough sedimentary rocks. Early vein muscovites have Middle Devonian 40Ar/39Ar dates of 380–370 Ma. Regional metamorphic biotites from Hill End have well constrained 40Ar/39Ar closing ages of 360–358 Ma (mid‐Famennian). The metamorphic (thermal) maximum which outlasted penetrative deformation, is estimated here by modelling to have been about 370 Ma (latest Givetian). This clearly places the earlier main deformation in the Middle Devonian. Deformation probably began by terminating trough deposition in latest Emsian to early Eifelian time and ended in early Givetian time at about 375 Ma ago. Published pressure and temperature data from the Hill End goldfield suggest that deformation thickened the 6 km sediment column to around 11 km. The thermal model suggests there was post‐deformation erosion of about 4 km and little if any further erosion occurred during Late Devonian to Early Carboniferous time. The shortening accompanying the inversion of the northern Hill End Trough may have been taken up in the region to the south, both east and west of the Copperhannia Thrust, and east of the southern termination of the Capertee High. The general conclusions are not affected by a new Devonian time‐scale discussed in Appendix 2.

The continental margin off east Tasmania and Gippsland: structure and development using new multibeam sonar data

The continental margin facing the southern Tasman Sea off southeastern Australia is of high petroleum and geological significance because it contains Australia’s richest oil province, the Gippsland Basin. Exploration activity in the region has concentrated on the shelfal part of this basin. Off Tasmania the upper margin is host to important deep sea trawl fisheries, and regional geophysical data suggest some long-term petroleum potential.In early 1997, 20,000 km2 of the margin were surveyed by the Australian Geological Survey Organisation, in cooperation with Scripps Institution of Oceanography and the University of Sydney. The SeaBeam 2000 multibeam sonar system of the US RV Melville was used to map the topography and character of the seafloor in unprecedented detail. The SeaBeam 2000 is a 12 kHz, 121-beam echo-sounder that collects both bathymetry and backscatter (sidescan) data across a swath of ~3.4 times the water depth. The survey also collected 3500 km of magnetic and gravity profile data.The margin off Gippsland is dominated by a large embayment 100 km across and floored by a ESE-trending chasm, the Bass Canyon, which is 60 km long and 10-15 km wide. The canyon has cut down about 2 km into the margin and is bounded to the north and south by very steep inner canyon walls 1000 m high. Sediments transported down the canyon debouch at its mouth, at~4000 m depth, and spread onto the abyssal plain via a network of distributary channels and levees. Sediment from the shelf is channelled into the entrance of Bass Canyon by three major, deeply-incised tributary canyons and a number of smaller ones. Bass Canyon has probably acted as a conduit for clastic sediment to the deep sea floor since breakup at ~80 Ma. Seismic profiles over the Bass Canyon complex show that canyon erosion has exposed sections of almost the entire Gippsland Basin sequence down to the Early Cretaceous and underlying basement. Numerous suitable dredge and core sampling sites in the canyons have been identified for a geological sampling program.Off east Tasmania, the survey showed the margin to be generally steep and rugged, with relatively little sediment having been deposited on the continental slope, except in narrow rifts, since breakup. The adjacent abyssal plain is commonly underlain by 2 km of Late Cretaceous-Cainozoic sedimentary section. The continental slope is cut by an extensive system of canyons, some more than 30 km long and 500 m deep. Large fault blocks on the lower slope show structural trends consistent with a NW-NNW rift direction and NE-ENE transfer direction. The upper slope appears to be underlain by a subsided Miocene carbonate shelf. Volcanics, of probable late Cainozoic age, are fairly widespread on the seafloor off northeast Tasmania. Such volcanic terrain includes a number of scattered cones, the largest 450 m high.