At this scale 1cm on the map represents 1km on the ground. Each map covers a minimum area of 0.5 degrees longitude by 0.5 degrees latitude or about 54 kilometres by 54 kilometres. The contour interval is 20 metres. Many maps are supplemented by hill shading. These maps contain natural and constructed features including road and rail infrastructure, vegetation, hydrography, contours, localities and some administrative boundaries. Product Specifications Coverage: Australia is covered by more than 3000 x 1:100 000 scale maps, of which 1600 have been published as printed maps. Unpublished maps are available as compilations. Currency: Ranges from 1961 to 2009. Average 1997. Coordinates: Geographical and either AMG or MGA coordinates. Datum: AGD66, GDA94; AHD Projection: Universal Transverse Mercator UTM. Medium: Printed maps: Paper, flat and folded copies. Compilations: Paper or film, flat copies only.

These documents have been scanned by the GA Library. Please refer to the document for contents.

These documents have been scanned by the GA Library. Please refer to the document for contents.

This bibliography mainly contains reports of those major surveys used to construct the 1976 1:5 million gravity map of Australia. The bibliography is listed in alphabetical order, and the list is numbered consecutively. Figure 1 relates the reference number to the area covered by each report. Most reports give the survey method, logistic information, the gravity meter number and its calibration details, the datum of horizontal coordinates, vertical coordinates and gravity, the accuracy of the reduced position and gravity data, a Bouguer anomaly map, and a description and geological interpretation of this map. Also included are selected publications on the progress of gravity mapping, on the establishment and refinement of a national gravity reference network of base stations to define datum and scale, and of the use of the mapped gravity anomalies in the definition of geological structure and in geodetic studies. A comprehensive bibliography of gravity in Australia has been prepared, and it is planned to make this available shortly.

Gravity features have been defined and named by the various authors who have interpreted the results of land and marine reconnaissance gravity surveys in Australia. In general, two classes of feature have been identified - gravity provinces and gravity units. A gravity province is a region where the gravity field is characterized by uniformity of some property, such as contour trend, gravity level, or degree of contour disturbance, which distinguishes it from neighbouring provinces. A gravity unit is a subdivision of a province. Neighbouring units are again distinguished from each other by differences in contour trend, gravity level, or degree of contour disturbance - but on a smaller scale. Many gravity features were originally defined from the results of individual reconnaissance surveys in isolated areas and have been shown to be inconsistent with the regional gravity pattern after more extensive coverage has been obtained. Land and marine gravity coverage is now virtually complete, and an attempt has now been made to rationalize gravity province boundaries and names over the whole of Australia and its continental margins. In all, 125 provinces have been defined and named. It is recommended that authors make use of the names when discussing regional gravity features.

A registry of stratigraphic names was started in BMR in 1949. In 1976 the Stratigraphic Names Index alone contains over 20 000 entries. The central registry now includes the following indexes: Author Index, Stratigraphic Name Index, Sheet Area Index, Basin Index, Subject Index, Reserved Name Index, and Definition Card Index.

The earliest known gravity measurements in Australia were made by French expeditions in 1819 and 1824, using pendulums at Sydney. Later in the 19th century, further pendulum measurements with an accuracy of about 10 mGal were made at various capital cities by observers from Britain, Bavaria, Austria-Hungary, Russia and Italy. A very early gravity meter was designed and constructed at Sydney University during the last decade of the century, but was used only experimentally. Reasonably accurate gravity meter surveys started about 1947. The Cambridge pendulums were used in 1950-51 to establish a national network of 59 stations with an accuracy of about 0.8 mGal; this was supplemented between 1950 and 1959 by gravity meter and pendulum measurements made as part of international surveys, which also helped to relate the Australian datum to the international network. Meanwhile, surveys, mainly for geophysical prospecting, were made by Government authorities, universities, and private companies; some of these surveys covered extensive areas and enabled compilation of a preliminary Bouguer anomaly map in 1959. Early marine gravity surveys included observations in nearby oceans with Vening Meinesz submarine pendulums, gravity measurements on offshore islands and reefs, and from 1956, underwater gravity meter surveys on the continental shelf. Two factors stimulated regional gravity coverage in 1959 - firstly the Petroleum Search Subsidy Act, which ensured that exploration data from subsidized surveys were publicly available, and secondly, use of helicopters for reconnaissance gravity coverage of the continent, which was completed in 1973. Gravity data at sea were obtained mainly from reconnaissance marine geophysical surveys carried out under contract to BMR between 1965 and 1973, but include also traverses by international survey vessels and exploration companies. Gravity meter calibration ranges were established in the main cities in 1960-61. Gravity values at the Cambridge pendulum stations were revised in 1962 using all relevant data, to establish a more accurate control network with standard errors ranging from 0.2 to more than 0.4 mGal for compilation of data from many surveys. These values were superseded by the Isogal Project of 1964-67, which gave values with standard errors of 0.1-0.2 mGal, in which several gravity meters were transported by aircraft along transcontinental east-west traverses. Values at the eastern ends of the traverses, forming part of the Australian Calibration Line (ACL), were established by a US Air Force survey in 1965. The accuracy of the ACL was significantly improved by Soviet pendulum measurements in 1972-74, and joint Soviet-Australian gravity meter measurements in 1973 - a precision of about 0.01 mGal being achieved.

Editorial

The Australian gravity field is analysed to determine whether the basement differs between regions of exposed basement and of covered basement (sedimentary basins). When the thickness of cover is allowed for, there is no systematic change in gravity variability from exposed to covered basement regions and the pattern of density differences is inferred to be similar in the two basement types. With one exception the trends of the gravity anomalies are continuous from covered to exposed basement regions; therefore geological structure and rock formations in the basement are considered to be continuous between the two kinds of regions. After making allowance for altitude and the effects of cover beds, the covered basement is calculated to have gravity anomalies that average 5 mGal less than the exposed basement. This gravity difference is probably caused by the two kinds of basement not being isostatically balanced relative to each other, rather than the basements having a different average density. No major differences between exposed and covered basement are apparent. It is likely that the two basement types have a similar history of formation, and consequently similar mineral potential.

Seismic refraction surveys in Australia and nearby marine areas provide data on crustal velocities and layer thicknesses. The averages of these at various places have been used to estimate a density-depth structure. By applying corrections for average elevation and free-air gravity, a crustal mass deficiency (CMD) is calculated for each site; this characterizes a standard crustal column with zero elevation and zero free-air anomaly, which is considered to be in isostatic equilibrium over a mantle of uniform density 3.32 t/m^3. The CMD ranges from about 13 kt/m^2 in the south-west of the continent, to about 21 in parts of Queensland; marine values range from 15 to 17 kt/m^2. The variations imply that isostasy on a broad scale is not complete at the base of the crust. As the gravity field indicates that departures from isostasy are comparatively small, compensation must occur partly in the mantle.