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This summary of palaeontological data derived from Meda #1 well is based on information provided in the original well completion report and its subsequent publication (Pudovskis 1959, 1962), updated with reference to more recent palaeontological and biostratigraphic research in the Canning Basin and elsewhere. No samples have been re-examined, but in some cases this would seem to be a requirement to resolve uncertainties in dating certain horizons.

This GA Professional Opinion report is one of a series of 4 reports being undertaken by the GA Groundwater Group under the National Collaboration Framework Project Agreement with the Office of Water Science (in DSEWPaC). TheOtway Basin in Victoria and South Australia is a priority coal-bearing sedimentary basin that is not currently slated for Bioregional Assessment.

Geoscience Australia (GA) was engaged by Sydney Water Corporation (SW) to review existing geological, geophysical and geotechnical data from the Sydney region in an effort to better understand seismic hazard in SW's area of operations. The main motivation is that this information can be used to improve SW's understanding of the level of earthquake risk to their infrastructure in order to support their asset management practices. Of particular interest is improving SW's understanding of asset damage or loss and potential network disruption following a large earthquake. One of the main factors influencing earthquake hazard in the Sydney Water area of operations is the likelihood of a large earthquake to the west of Sydney on what is known as the Lapstone Structural Complex. Research conducted by Geoscience Australia suggests that large earthquakes in the Lapstone Structural Complex are extremely rare (i.e. they may only happen once every few million years). This means that the area probably does not contribute as much to the seismic hazard in Sydney as has been previously thought. An equally important factor is the response of near-surface geological materials to earthquake shaking. Two seismic site classification maps for the Sydney region have been developed here to characterise materials in terms of their potential response. One uses the modified United States National Earthquake Hazard Reduction Program (NEHRP) classification scheme, while the other uses the Australian Earthquake Loading Standard (AS1170.4-2007) classification scheme. Assessment and validation of the classifications against independently acquired data from sub-surface investigations in the region suggest that both classifications provide a satisfactory representation of the distribution of materials and their potential to amplify earthquake energy. The exception to this outcome is the area underlain by the Botany Basin, where geophysical investigations and drilling data have identified the thicker basin fill sediments as having the potential to effectively increase earthquake hazard. The aforementioned AS1170.4 site classification was used to generate Australian Standard (AS1170.4-2007) earthquake hazard maps covering SW's area of operations. The analyses were completed for three spectral periods (0 s, 0.2 s and 1.0 s) and two return periods (500 years and 800 years). Results show that earthquake shaking at 0.2 s spectral period produced the highest hazard at both return periods. Overall, areas characterised by the presence of unconsolidated Cenozoic sedimentary units exhibited the highest earthquake hazard under all conditions. The modified NEHRP site classification outputs were used to produce a probabilistic seismic hazard assessment for the SW area of operations, using the same spectral periods and return periods. Comparison of the AS1170.4-2007 and EQRM outputs reveal several key findings. Firstly, the use of the modified NEHRP site classification scheme better differentiates the properties of geological materials, and therefore the seismic hazard, across the SW area of operations. Secondly, the probabilistic seismic hazard assessment produced values that were up to 6 times lower than those generated using the Australian Standard methodology. Lastly, regardless of the site classification schema or hazard methodology employed, areas characterised by relatively unconsolidated Cenozoic (predominantly Quaternary) sedimentary deposits always represented the highest levels of earthquake hazard.

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Phase 3a of the Broken Hill Managed Aquifer Recharge (BHMAR) project is tasked with assessing whether a sustainable ground water extraction approach, including MAR, is a feasible option for securing Broken Hill's water supply in times of drought. More specifically, the project is charged with determining, with a defined level of confidence, whether at least 3 years water supply (~30 GL), at a similar salinity to that already available for Broken Hill would be available at all times through these new arrangements. This interim report documents the preliminary findings of the Phase 3a study, which is focussed on a priority target immediately south of Menindee.

This study was aimed at testing whether the regional tectonostratigraphic history established for Australia's premier hydrocarbon province, the North Carnarvon Basin, is applicable to the less well endowed, western Exmouth Sub-basin on its southern margin. This was achieved through the first systematic analysis of the structural architecture of the basin utilising 3D seismic and potential field data. Analysis focused on the Late Triassic to present basin history which highlighted some significant departures from the established tectonostratigraphic paradigm. The results indicate rifting occurred in two separate events. The first occurred under an east-west paleostress field and developed north striking faults controlled by Phanerozoic and Carbonifer to Permian pre-rift structures. This phase of basin development climaxed in the Callovian which resulted in the development of a significantly under filled basin and the deposition of anoxic petroleum source rocks. The first phase of rifting ceased in the Oxfordian and was followed by post-rift subsidence and later, previously unrecognised, Oxfordian to Tithonian south directed inversion localised above Proterozoic basement west-northwest oriented structures. This inversion event occurred under a detached stress filed which resulted in the formation of doubly plunging fault propagation anticline above south directed thrusts which terminated at a depth of 5-6 km. accompanied by contemporaneous extension along north to north-northeast striking fault segments in the upper most crust. Inversion ceased at the base of the Cretaceous and was followed by the second phase of rifting this time under west-northwest extension which resulted in rift fault system reorganisation and new normal fault growth. Rifting terminated at the onset of nearby Valanginian sea floor spreading. Post-rift thermal subsidence followed punctuated by variably directed periods of basin inversion over the last 130 Myrs. This long phase of inversion was enabled by an abnormally thick pre-rift lithosphere which took a long time to cool following rifting and hence could accommodated shortening over this long time span. A consideration of this thick lithosphere in hydrocarbon charge modelling in the Exmouth Sub-basin may lead to a change in the prevailing view that the main hydrocarbon charge occurred before the deposition of the regional seal, thereby making this apparently less well endowed basin more prospective for future exploration. A new understanding of the tectonstratigraphic evolution of the area has also highlighted new petroleum plays in previously un recognised structures some of which have been unaffected by Valanginian fresh water flushing and hence may contain non-biodegraded hydrocarbons.

Legacy product - no abstract available

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