The Brunhes/Matuyama (B/M) polarity transition (0.78 Ma) marks the end of the last major period of reversed polarity of the Earth s magnetic field. Weathered regolith materials with reversed polarity chemical remanent magnetisation (CRM) must, therefore, predate the B/M transition. Reversed polarity magnetisation can be preserved in a wide variety of regolith materials in eastern Australia, particularly in oxidising environments. At Sellicks Beach and Hallett Cove near Adelaide, the B/M transition is identified in a strongly mottled unit, the Ochre Cove Formation. In Canberra, strongly weathered fan gravels on the east side of Black Mountain have a mixture of reversed and normal polarities, indicating initial weathering and deposition before 0.78 Ma and continued weathering since then. In north Queensland, a soil formed on a 2.46 Ma basalt flow has reversed polarity in the lower B horizon, indicating that, over the last 0.78 Ma, pedogenesis has had little or no effect on the secondary iron minerals carrying the magnetic remanence in that part of the profile.

Dinoflagellates offer a reliable method for distinguishing the Late Miocene-Early Pliocene Bookpurnong beds from lithologically similar marginal marine sediments, such as the Winnambool Formation deposited during Oligocene-Middle Miocene transgressions. Species largely or wholly restricted to the Bookpurnong beds and correlatives in the central west Murray Basin include Melitasphaeridium aequabile, M . choanophorum, Tectatodinium psilatum , and (frequent) Tuberculodinium vancampoae. Species diagnostic of the older Murray Group correlatives, such as the Geera Clay and Winnambool Formation, include Apteodinium australiense and Pentadinium laticinctum.

Widespread clearing of native vegetation has dramatically increased recharge in the Mallee region by up to two orders of magnitude. The resultant rising water tables have caused land salinisation problems in low lying areas and, in the long term, will increase saline groundwater inflows to the River Murray with a consequent rise in river salinity. Computer modelling suggests that, 50 years after the water table begins responding to the increase in recharge, an increase of 70 Electrical Conductivity (EC) units in river salinity will occur at Morgan. Broadscale revegetation in strategic areas adjacent to the river will reduce saline groundwater inflows, and the economic and social aspects of this measure should be investigated.

36CI analyses of groundwater samples from 18 wells in the Victorian and South Australian Mallee region of the Murray Basin have been carried out using the technique of accelerator mass spectrometry. Results of these analyses are discussed and presented as evidence for significant recharge from rainfall over much of the study area to the underlying Murray Group limestone aquifer. In addition, results indicate areas where further 36CI measurements of Murray Mallee groundwater would provide useful hydrological information on both recharge and discharge mechanisms.

Large volumes of saline water are produced in the Murray Basin, principally from naturally occurring saline groundwater discharge to rivers and lakes and discharge induced by land use change, and subsurface drainage effluent from irrigation areas. Disposal of this saline water is fundamental to salinity and land management strategies. It has traditionally involved either River Murray or non-River Murray options, and should preferably include elements of both. Reuse of saline water is probably the major disposal technique in irrigation regions. Total reuse is limited by eventual soil degradation and groundwater salinisation; maintaining the appropriate salt balance in the root zone is essential for long term viability. River Murray options are either as uncontrolled outflow (mostly non-point saline inflows) or controlled outflow (e.g. from groundwater pumping, flushing of evaporation basins). Controlled outflow is limited by salt load, time of outfall and frequency of floods. Dilution flows to reduce river salinity are generally not economic. Non-River Murray options are evaporation basins (with or without salt harvesting), aquifer disposal, desalinisation and pipelines to the sea. Use of River Murray lagoons and backwaters to dispose of irrigation drainage waters often leads to severe environmental costs. Major existing and planned evaporation basins are reviewed. Full engineering, hydrogeological and environmental investigations should be encouraged; poorly sited evaporation basins should be evaluated and their use phased out if unacceptable. Detailed consideration of short and long term effects of leakage is essential. Most shallow disposal bores cause significant adverse effects by displacing highly saline groundwater to the Murray River. This practice should be phased out. The use of deep disposal bores requires detailed investigations, and is unlikely to be extensive. A good understanding of the rate of transmission of pressure and salt in the aquifer is critical in aquifer disposal. Desalination is very expensive, and not economic or practical. Pipelines to the sea have been shown to be highly uneconomic, although further analysis may favour this option in the long term. All disposal options are economically evaluated and contrasted. A key factor in the economics of disposal is salinity of the water. For low-salinity water, reuse and controlled outfall (often with holding basins) via the River Murray are clearly most economic. As salinity increases, evaporation basins become more economic. Most other options (except for well located shallow aquifer injection bores) are much more expensive. Public perceptions of feasible disposal options are often poor. Environmental effects can be grouped into those with short term costs to the ecosystem and those with long term hydrogeological consequences. Investigation and evaluation of environmental effects of the major salt disposal options (principally evaporation basins) are now becoming key factors in the choice of the preferred option. An effective saline water disposal strategy for the Murray Basin is one of the highest priorities in salinity management. Economic and environmentally acceptable options exist now, although they may be politically difficult at the local scale. More consideration of how to manage the naturally occurring discharge areas of the Mallee may have significant long term benefits. Best use should be made of all technically and environmentally feasible disposal sites.

The Bremer Basin underlies part of the upper continental slope of offshore southwest Australia. It occupies an area of 9000 km2, and contains a sedimentary pile probably 10 km thick in water depths of 200-3000 m. Though not tested by drilling, the basin is covered by a grid of seismic data. By analogy with the Eyre Sub-basin to the east, the Bremer Basin probably contains Late Jurassic to Barremian continental deposits overlain by Albian and Late Cretaceous marine deposits with a veneer of Tertiary open-marine carbonates of variable thickness. The Bremer Basin formed during the period of continental extension that preceded the breakup of Australia and Antarctica in the mid-Cretaceous. However, Triassic (?and older) extension and spreading events in the Perth Basin, a short distance to the west, are likely to have influenced its evolution. Basement structural trends in the basin indicate an old east-west-trending (?Palaeozoic) fabric that has been overprinted by north-northwesterly oriented Jurassic-Cretaceous extension and wrenching. The resultant structure is complex, particularly where the Palaeozoic and Mesozoic trends intersect. The hydrocarbon potential of the Bremer Basin is currently unknown. However, by analogy with the Eyre Sub-basin, potential source and reservoir sections can be inferred to exist, although the presence of a regional seal and a heatflow regime adequate for the generation of hydrocarbons is less certain. Potential trapping mechanisms for hydrocarbons include wrench-induced anticlines, clastic aprons adjacent to boundary and transfer faults, and stratigraphic traps within dipping Neocomian rocks beneath a major angular unconformity.

Sediments of the Late Palaeozoic Urana Formation in infrabasins beneath the Cainozoic Murray Basin include glaciomarine diamictite, fine-grained sediment, sandstone, and conglomerate facies. The facies assemblage is dominated by paratillites, formed by ice-rafting, and fine-grained sediments with a small ice-rafted component. Rhythmically bedded siltstone and claystone, sediment gravity-flow diamictites, traction-current deposits, and, possibly, subglacial tillites are also present. Interpretation of the facies indicates that grounded-ice deposits are absent from the glaciomarine sequence over large areas of the basin and has enabled estimation of the likely limits of grounded ice. Palaeontological and sedimentological evidence suggests that these rocks were deposited towards the end of the major Late Palaeozoic glaciation of southeastern Australia.

Sediments on the continental shelf of eastern Australia increase in carbonate content away from the present shoreline. However, the high values of the outer shelf sands show little latitudinal variation, both tropical and temperate continental shelves being mantled with sediments which are relatively pure carbonates. Thus a high calcimass productivity is not restricted to tropical regions. However, the types of carbonate-secreting organisms do show marked latitudinal variations. North of latitude 24°S the outer continental shelf is dominated by the Great Barrier Reef, and inter-reef and outer shelf sediments contain the remains of hermatypic corals and calcareous green algae, mainly Halimeda, together with varying amounts of foraminifera, Mollusca, Bryozoa, and calcareous red algae. Corals and Halimeda are not present in the sediments south of 24°S, which consists of foraminifera, mollusca, bryozoa and calcareous red algae. The bryozoan content of the sediments increases to the south, and between 38° and 44°S bryozoans become the dominant component of the outer shelf sands. Present-day sea-surface temperature and salinity data have been analysed to predict the distribution of carbonate particle associations. The observed distribution agrees with the predicted one, but the presence of relict carbonate sediments must be taken into account.

Concentrations of heavy minerals in the prograded coastal sequence of southeastern South Australia are generally low, partly as a result of the high content of locally derived biogenic carbonate in many of the sediments. Terrigenous input to the nearshore region appears to have been relatively slight, and the operation of concentrating mechanisms minimal. The highest heavy-mineral concentrations recorded in the area (up to 1.2% total heavies) occur in a sand of probable Pliocene age underlying Quaternary beach and dune deposits. In general, the heavy-mineral suite present in the sediments consists of between 25 and 45 percent magnetite-plus-ilmenite, 5 and 20 percent leucoxene, 5 and 25 percent zircon, 5 and 30 percent tourmaline, and between 0 and 10 percent amphibole, epidote, rutile and garnet. Andalusite, sillimanite, kyanite and staurolite occur as minor components in many assemblages. Sialic igneous, reworked sedimentary, metamorphic and to a slight extent mafic igneous components are present. Probable sources include the igneous rocks of the Padthaway Ridge, metamoraphic and sedimentary rocks of the Fleurieu Peninsula and Kangaroo Island, and older Tertiary sediments. Variations in the suite are defined by cluster and Q-mode factor analysis. Higher concentrations of heavy minerals occur within the older (probably Pliocene) ridges of the western Victorian Murray Basin. These ridges which approximately parallel the southeast South Australian ridge sequence, are siliceous, and commonly contain thin bands of concentrated heavy mineral (up to 20% total heavies in the bands) in the lower part of the Parilla Sand. The suite is mineralogically mature (generally 50-70% opaque, 15-30% tourmaline, 3-5% rutile, 5-15% zircon and 1-3% others) and differs considerably from that present in the southeast South Australian sequence. The difference reflects differences in provenance of the two areas and the probable modification by intrastratal solution of the assemblages originally present in the older deposits.