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.

New earthquake risk maps of Tasmania have been prepared depicting risk by contours of peak ground velocity, acceleration and intensity with a 10 per cent probability of being exceeded in a 50 year period. The Cornell- McGuire method was used. The maps are based on seismicity up to the end of 1984, including the events of the 1883-1892 earthquake swarm east of Flinders Island and other historical data. The earthquake process was assumed to be Poissonian, so foreshocks and aftershocks were eliminated from the analysis. For this earthquake risk assessment, average eastern Australian background seismicity and attenuation for average site conditions were used. The earthquake source zones most affecting the risk in the Tasmanian region are the West Tasman Sea Zone and the Western Tasmanian Zone. The West Tasman Sea Zone, east of Flinders and Cape Barren Islands, appears to have been the site of the 1883 - 1892 swarm, with at least three intensity-deduced Richter magnitude 6.0- 7.0 events. Consequently, the highest risk land areas are Flinders and Cape Barren Islands, which lie predominantly between the 60 mm.s-1/0.6 m.s-2 and 120 mm.s-1/ 1.2 m.s-2 contours, with the risk increasing to the east. In the Western Tasmanian Zone, the largest event recorded was in 1880. It had an intensity-deduced Richter magnitude of 5.5. The northern part of western Tasmania (enclosed by the 59 mm.s-1/ 0.55 m-2 contour) is the second highest risk region. At Hobart and Launceston, outside the source zones, the values are 23 mm-1 / 0.21 m.s-2 and 30 mm.s-1/ 0.29 m.s-2 respectively, corresponding to a 10 per cent chance of an intensity MMIV - V being exceeded in a 50-year period. However, it appears that site amplification of strong ground motion takes place in some parts of Launceston, and this should be considered when zoning for the Building Code. The chief contributions to uncertainty in the estimates of earthquake risk are uncertainties in early earthquake locations and magnitudes, and in strong ground motion attenuation.

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 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.

From a study of middle to late Eocene calcareous nannofossil assemblages in four sections in the Otway Basin of southeastern Australia, a sequence of biostratigraphic events has been deduced, spanning the interval from the lowest appearance of Cyclicargolithus reticulatus (middle Eocene) to the disappearance of Discoaster saipanensis (latest Eocene). The sequence is compared with its coumerpart in New Zealand, and is placed against the planktic foraminiferal P. zones of the tropics. The previously determined foraminiferal biostratigraphy of the sections studied has been compared with the nannofossil biostratigraphy, and, as a result, the local highest appearance of the foraminiferid Acarinina primitiva is now placed in zone P. l3 of the tropics , and not P.12 or P.14, as previously. The disappearance up the section of the foraminiferid Acarinina collactea is found to be locally inconsistent with other evidence. During the middle Eocene, marine ingressions, represented by isolated nannofossil assemblages, occurred in the Gambier Embayment of the western Otway Basin, but did not reach the Browns Creek area, eastern Otway Basin, attesting to the diachroneity of Eocene marine sedimentation in the basin . The diachroneity is also indicated by transgressive rock units in the Gambier Embayment. The ingressions seem to coincide with a major change in the sea-floor spreading rate south of Australia. During the latest middle to early late Eocene, a major transgression began synchronously in widely separated areas across the basin. The upper Eocene section in the Gambier Embayment represents condensed sedimentation and ends in a sharp disconformity, indicated by the simultaneous disappearance of Cyclicargolithus reticulatus and Discoaster saipanensis. At Browns Creek, that part of the section between the highest appearances of C. reticulatus and D. saipanensis is thick, suggesting relatively rapid rates of sedimentation. However, in the expanded part of the section at Browns Creek and also at Castle Cove, there is evidence that extreme shoal conditions existed as a result of imbalance between sedimentation and subsidence. During the middle and late Eocene, conditions along the Australian southern margin were generally temperate, with surface-water temperature decreasing eastward, and the depositional environment was essentially shallow marine - nearshore or shelf.