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The Liverpool Plains in northern New South Wales contain some of the best agricultural land in Australia and are underlain by extensive smectite clay-dominated soils sourced from weathering the alkali basalts of the Liverpool Ranges. It had been thought that a relatively simple geological model explained the underlying Cenozoic sequence with salt-rich clays of the Narrabri Formation overlying sands and gravel aquifers comprising the Gunnedah Formation. Extensive groundwater modelling based upon this simple conceptualisation has been used in management plans proposed by the mining and agricultural industries. A 31.5 m core has been recovered using minimally disturbed triple-tube coring methods at Cattle Lane (Latitude –31.52° S, Longitude 150.47° E) to resolve uncertainty concerning the aquitard status of the upper layer. Recovered core has been examined and tested to determine grainsize, cation-exchange capacity, X-ray diffraction, X-ray fluorescence and microscopic examination of granular components. These measurements complement surface and borehole geophysical techniques, hydrogeological data and hydrochemical analysis of water samples recovered from a series of specially constructed piezometers adjacent to the cored hole. The sequence overlies a Late Cretaceous channel cut into Permian bedrock at 91 m depth with sands and clays below 31.5 m considered to represent various alluvial fill events mostly occurring since the Early Pliocene. Erosion of Late Eocene alkali basalts on the Liverpool Ranges, with the formation of smectite clays, pedogenic carbonates and with the addition of quartz from both eolian sources and locally derived from adjacent Triassic sandstone hills, provides the great majority of the sediment recovered from the cores. Late Pleistocene (114 ka) to Holocene ages were determined for the core from three optically stimulated luminescence (OSL) measurements on fine sands (13, 23 and 29 m BG). Detailed examination has failed to detect any evidence of a boundary between Narrabri and Gunnedah formations revealing rather a gradual change in dominance of clays and silts over sands and gravels embedded in a clay-rich matrix. This result challenges the conceptualisation used to conduct groundwater modelling on the Liverpool Plains. [ABSTRACT FROM AUTHOR]

The Frome airborne electromagnetic (AEM) survey was designed to provide reliable pre-competitive AEM data to aid the search for energy and mineral resources around the Lake Frome region of South Australia. Flown in 2010, a total of 32,317 line kilometres of high-quality airborne geophysical data was collected over an area of 95,450 km2at a flight line spacing mostly of 2.5 km, opening to 5 km spaced lines in the Marree–Strzelecki Desert area to the north. The Lake Frome region hosts a large number of sandstone-hosted uranium deposits with known resources of ∼60 000 tonnes of U3O8including the workingIn SituRecovery operations at Beverley, Pepegoona, Pannikin and Honeymoon, and deposits at Four Mile East, Four Mile West, Yagdlin, Goulds Dam, Oban, East Kalkaroo, Yarramba and Junction Dam. The aims of the Frome AEM Survey were to map and interpret critical elements of sandstone-hosted uranium mineral systems including basin architecture, paleovalley morphology, sedimentary facies changes, hydrological connections between uranium sources and uranium deposition sites and structures. Interpretations of the data show the utility of regional AEM surveying for mapping crucial elements of sandstone-hosted uranium mineral systems as well as for mapping geological surfaces, structures and depth of cover over a wide area. Data from the Frome AEM Survey allow mineral explorers to put their own high-resolution AEM surveys into a regional context. Survey data were used to map and interpret a range of geological features that are associated with, or control the location of, sandstone-hosted uranium mineral systems and have been used to assess the uranium prospectivity of new areas to the north of the Flinders Ranges. [ABSTRACT FROM PUBLISHER]

Cenozoic fluvial sediments present west of the Meckering Line occur at similar elevation ranges (mostly 200-260 m AHD) in the largely rejuvenated forested landscapes of the Darling Plateau between the Helena River catchment and the south coast of Western Australia. These widespread paleovalley sediments are more continuous than previously recognised, and possess common hydrogeological characteristics. The upper parts of catchments in southwest Western Australia are flat and poorly drained with widespread salt lakes and wetland systems developed on the sediments. The lower rejuvenated landscapes below the base of remnant sediments, which are locally marked by saline springs and right angle changes in river courses, have undulating topography with well-defined drainage lines cut into competent basement rocks. This paper identifies groundwater flow systems associated with the paleovalley sediments in three varied catchments and describes the role of the Cenozoic sand aquifer in the development and potential management of dryland salinity. Groundwater flow in the Cenozoic paleovalley sand aquifer has more significance for land and water salinisation than that in the local weathered basement. The sand aquifer is a conduit for salt mobilised from weathered basement following land clearing. Erosion of the sedimentary profile by rejuvenation has exposed this sand aquifer within specific elevation ranges in modern drainages facilitating saline groundwater discharge, and land and water salinisation. In the Helena River catchment 63% of the salt load to the Mundaring Reservoir is discharged through this sand aquifer in only 30% of the streamflow. Such mismatched salt load and flow means southwest landscapes respond differently to key dryland and stream salinity management actions. Revegetation to reduce the salt load should target areas of weathered basement locally discharging saline groundwater to the sand aquifer. Reforestation elsewhere in the rejuvenated bedrock landscape can, by contrast, reduce the streamflow (that is diluting large salt loads from the remnant sedimentary landscapes) and hence raise the overall stream salinity. [ABSTRACT FROM AUTHOR]

The Bland Basin is the broad alluviated paleovalley of Bland Creek, a tributary of the Lachlan River in the central part of New South Wales, Australia, within the drainage basin of the Murray-Darling river system. It covers about 4000 km2 and contains up to 120 m of terrestrial sediments, interpreted as being deposited by alluvial, colluvial, lacustrine/paludal and eolian processes. It is undated, but is likely to be coeval with the downstream contiguous fill of the Lachlan River paleovalley, dated elsewhere by palynology as Miocene to Holocene. The southwestern part of the basin has been studied in detail using airborne geophysics (electromagnetics, magnetics and gamma-ray spectrometry) and drilling. The small erosional catchment area of the modern basin surface has resulted in a paucity of sediment available for deposition in the basin, but the drainage base-level has been driven by the rate of sedimentation of the Lachlan paleovalley downstream of the basin. Therefore, most of the sediment derived from the catchment has been trapped in the basin rather than being transported downstream and into the Lachlan paleovalley, and at times large lakes and/or swamps have formed in the central part of the basin. The sediments in the southwest of the basin are dominated by clay and silt, with local sand and gravel, mostly in basal gravelly sand and a sandier interval in the middle part of the sequence. Quartz silt derived from eolian dust is a major component of the upper part of the sedimentary sequence. Geophysical responses of the sediment include high conductivity due to saline groundwater, low gamma response dominated by thorium decay emissions due to the leached nature of the sediment, and short-wavelength-low-amplitude magnetic anomalies resulting from local concentrations of detrital maghemite-rich gravel formed during weathering in the catchment area. Broad valleys draining to the Lachlan River west of the Bland Basin may contain similar mud-dominated Neogene basins, but a lack of drill data precludes detailed interpretation. [ABSTRACT FROM AUTHOR]

This paper focuses on a small back-barrier sand-island on the southeast coast of Queensland. The freshwater lens in the study area exhibits anomalously high short-range salinity gradients at shallow depths, which cannot be explained using a standard seawater intrusion model. The island groundwater system consists of two aquifers: a semiconfined aquifer hosting saline to hypersaline groundwater and an overlying unconfined freshwater aquifer. The deeper aquifer is semiconfined within an incised paleovalley, and groundwater flow is restricted to an east - west direction. Tidal response observations show that the tidal signal propagates far more rapidly and is of much higher magnitude in the semiconfined aquifer than the unconfined aquifer. The tidal wave-pulse amplitude is also subject to greater attenuation in the unconfined aquifer. A conceptual hydrogeological model illustrates how upwelling of hypersaline groundwater, induced by density-dependent flow and tidal pumping, has contaminated the shallow groundwater resource. Salinisation at shallow depths is restricted to an area proximal to the paleovalley aquifer. The spatial distribution of lithological heterogeneity is an initial limiting control on the movement of the upwelling saline plume. The extent of shallow groundwater contamination is also limited by the presence of a baroclinic field, resulting from lateral variations in fluid density. Hydrochemical signatures have been used to support the model hypothesis and link the salinisation of fresh groundwater with the semiconfined aquifer as opposed to the surrounding estuarine surface water. The geometry and thickness of the freshwater lens are further controlled by the presence of the largely impermeable bedrock paleosurface between 9 and 12 m depth. The combination of hypersaline groundwater and hydraulically restrictive lithology at shallow depths has produced excessive thinning of the freshwater lens, demonstrating that the application of a model such as the Dupuit - Ghyben - Herzberg relationship would grossly overestimate the available groundwater resource. [ABSTRACT FROM AUTHOR]