From 1 - 10 / 1823
  • The Early Cretaceous Gage Sandstone and South Perth Shale are a prospective reservoir-seal pair in the Warnbro Group of offshore Vlaming Sub-basin, Western Australia. Gage Sandstone reservoir plays include post-breakup pinch-outs against the Valanginian Unconformity, and 4-way dip closures with the South Perth Shale forming the top seal. Deposited as a lowstand component of the deltaic South Perth Supersequence, the Gage Lowstand Fan (previously referred to as the Gage Sandstone) infilled palaeotopographic lows of the Valanginian breakup unconformity. Sequence stratigraphic analysis was used to characterise the reservoir-seal pair by integrating 2D seismic interpretation, well log analysis and new biostratigraphic data. Palaeogeographic mapping of the South Perth Supersequence reveal a series of regressions and transgressions that lead to the infilling of the central palaeodepression. The Gage reservoir is a sand-rich submarine fan system and ranges from canyon-confined inner fan deposits to middle fan deposits on a basin plain. Major sediment contributions were from north-south trending canyons adjacent to the Mandurah Terrace. More detailed seismic facies mapping and well log analysis of the Gage Lowstand Fan determined that the sand sheets in the distal middle fan and stacked channelized sands in the inner fan may provide an extensive reservoir of good to excellent quality. Seal quality varies greatly and may explain the lack of exploration success at some structural closures. A re-evaluation of the regional seal determined the extent of the pro-delta shale facies within the South Perth Supersequence that provides an effective seal for the underlying Gage reservoir. 3D geological modelling confirms that the Gage reservoir exhibits properties suitable for hydrocarbon entrapment and CO2 storage. Migration path analysis identified the presence of multiple structural and stratigraphic closures at the top of the Gage reservoir, with the most favourable located in the Rottnest Trough. Previous petroleum systems modelling concluded that the maturity of some source rocks in the sub-basin likely occurred after the deposition of the effective seal. Deep-seated faults, penetrating the syn-rift section, are in direct contact with the Gage reservoir and it could be actively receiving hydrocarbon charge.

  • The existence of two Formations, the Laurel and Gumhole, in the Upper Devonian to Lower Carboniferous Fairfield Group from the Lennard Shelf in the Canning Basin has been established during field studies and confirmed using a multivariate analysis based on petrographic and geochemical data. Limestones of the Gumhole Formation are generally characterised by a dominance of either ooids or brachiopods, or the presences of bryozoa, as well as higher levels of Mn, Fe, Pb, Zn and the ratio Ca/Mg than are present in the limestones of the Laurel Formation, which are characterised by the presence of either pelecypods or silt, and higher levels of Mg, Sr, and the ratio Sr/ Ca. For the study, two representative groups of limestones from these formations were analysed. The analysis involved a taxonometric technique incorporating classification, ordination and diagnostic programs, and utilized in all 19 petrographic and 14 geochemical attributes. In both groups, at least 74 per cent of the samples were successfully differentiated on the criteria presented.

  • Data presented elsewhere in this issue (Page, Blake, and Mahon, 1976) provide some of the first ages from The Granites-Tanami Block. Unfortunately it did not prove possible to date or even adequately sample the weathered low grade metasediments and metavolcanics of the Tanami complex, clearly the oldest exposed component of the block. For this reason age data pertaining to the Halls Creek Group, the suggested correlative of the Tanami complex in the Kimberley region to the northwest (Page et al., this volume, Fig. 1), are now reinterpreted in an attempt to arrive at a reasonable estimate of the age of these old rocks. In considering the available information on the geochronology of this part of Australia it is also pertinent to review the age of the Whitewater Volcanics, Castlereagh Hill Porphyry and Bow River Granite, which form a Lower Proterozoic comagmatic suite overlying and intruding the Halls Creek Group in the Halls Creek Mobile Zone.

  • A new rock unit, the Bullara Limestone, is proposed for a Late Oligocene bioclastic limestone, which is probably restricted to the subsurface of Rough Range. The Bullara Limestone is a lateral equivalent of the lower part of the Mandu Calcarenite, and contains a Tertiary lower e stage larger foraminiferal fauna and a Zone N.3 planktic fauna.

  • Seismic reflection profiles over the southwestern margin of the Exmouth Plateau, which have been tentatively tied to the Northwest Shelf stratigraphic sequence, indicate that rocks of probable Permian to Early Tertiary age form bedrock on the lower continental slope and probably crop out in places. Water depths range from 1400 to 4000 m. It is surmised that the rocks present include pre-Late Jurassic fluvial, deltaic and shallow marine sandstone, siltstone and shale; Late Jurassic to Neocomian deltaic sandstone, siltstone and shale; mid Cretaceous shallow marine shale; Late Cretaceous shelf limestone and Cainozoic foraminiferal ooze. The Exmouth Plateau is cut by normal faults which are predominantly downthrown oceanwards and trend north-northeasterly across most of the area, except near the southwestern margin where they trend northwesterly. Faulting occurred primarily in the Middle to Late Jurassic and led to formation of the north-western and northern margins by seafloor spreading. A major anticline, which parallels the southwestern margin, has one limb truncated by the lower continental slope, probably resulting in older rocks cropping out in places. Deep Sea Drilling Project results on the Cuvier Abyssal Plain indicate that the southwestern margin formed in the Late Cretaceous, either as a transcurrent fault associated with seafloor spreading or by collapse along normal faults. Sampling of outcrops along the southwestern margin would enable the sequence to be dated more reliably and this would permit the theories of geological evolution and favourable petroleum potential of the Exmouth Plateau to be tested.

  • Nettletons concept of density profiling can be utilised to give useful estimates of the bulk density of topographic features. These estimates can be used to infer the composition of such topography, or to assist in the interpretation of local gravity anomalies. Two methods that facilitate multiple density profiling over elongate topography are presented. One is a simulation reduction method utilising the two-dimensional line integral formula of Talwani, Worzel and Landisman (1959). It enables data from any detailed gravity traverse crossing an elongate topographic feature at right angles to be automatically reduced by computer to a set of multiple density Bouguer profiles. From these profiles, the bulk density of the topographic feature can be estimated by visual correlation. The other is a graphical method of converting a set of multiple density Bouguer profiles directly to point density estimates, without the need for visual correlation. Both methods are theoretically exact for the ideal case. A visual correlation determination of 2.85 ± 0.05 g cm^-3 is demonstrated for a traverse crossing the 300 m high Harts Range, Northern Territory, and three point determinations of 2.97,2.97, and 2.99 g c^-3, for a traverse crossing the 100 m high Fraser Range, Western Australia.

  • Categories  

    The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. The terrestrial dose rate grid is derived as a linear combination of the filtered K, U and Th grids. A low pass filter is applied to this grid to generate the filtered terrestrial dose rate grid. This GSWA Murgoo Doserate Grid Geodetic has a cell size of 0.00042 degrees (approximately 44m) and shows the terrestrial dose rate of the Murchison 1 (Murgoo), WA, 2011. The data used to produce this grid was acquired in 2011 by the WA Government, and consisted of 131101 line-kilometres of data at 200m line spacing and 50m terrain clearance.

  • Categories  

    Digital Elevation data record the terrain height variations from the processed point- or line-located data recorded during a geophysical survey. This GSWA Murgoo Elevation Grid Geodetic is elevation data for the Murchison 1 (Murgoo), WA, 2011. This survey was acquired under the project No. 1239 for the geological survey of WA. The grid has a cell size of 0.00042 degrees (approximately 44m). This grid contains the ground elevation relative to the geoid for the Murchison 1 (Murgoo), WA, 2011. It represents the vertical distance from a location on the Earth's surface to the geoid. The data are given in units of meters. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose.

  • Categories  

    The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This radiometric potassium grid has a cell size of 0.00042 degrees (approximately 44m) and shows potassium element concentration of the Murchison 1 (Murgoo), WA, 2011 in units of percent (or %). The data used to produce this grid was acquired in 2011 by the WA Government, and consisted of 131101 line-kilometres of data at 200m line spacing and 50m terrain clearance.

  • Categories  

    The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. The terrestrial dose rate grid is derived as a linear combination of the filtered K, U and Th grids. A low pass filter is applied to this grid to generate the filtered terrestrial dose rate grid. This GSWA South West 1 Moora Doserate Grid Geodetic has a cell size of 0.00042 degrees (approximately 43m) and shows the terrestrial dose rate of the South West 1 (Moora), WA, 2011. The data used to produce this grid was acquired in 2011 by the WA Government, and consisted of 137623 line-kilometres of data at 200m line spacing and 50m terrain clearance.