Special demagnetising apparatus was constructed to study the stability of several samples of basic igneous rocks from three localities in eastern Australia, particular emphasis being placed on the reliability of the directions of NRM. The direction of primary magnetisation acquired when the rocks first cooled was determined for samples at all three sites. Mesozoic dolerite from Red Hill Dyke in southern Tasmania has little or no secondary magnetisation and the mean direction of NRM is representative of the Jurassic in Tasmania. There is no evidence of systematic error due to stress or shape, and therefore the direction of NRM is a reliable estimate of the direction of the geomagnetic field at the time of intrusion. Devonian Nethercote basalt from southern New South Wales can be divided into two distinct groups, one in which the NRM is completely unaffected in either direction or intensity by demagnetisation in peak alternating fields of up to 1000 oersteds, and the other in which secondary magnetisation completely masks any primary magnetisation that may be present. Tertiary basalts from southern New South Wales show a wide range of stability. The NRM consists of primary TRM and varying proportionate amounts of secondary magnetisation, which is almost certainly viscous and which was probably acquired in the present Earth's field. The stability shown by the three rock types makes it more probable that previous palaeomagnetic results, which span a long period from Devonian to Tertiary, form a reliable record of the geomagnetic field in Australia.The general effects of alternating demagnetising fields are also discussed and a comparison made between the theoretical predictions and the data obtained.

Legacy product - no abstract available

Legacy product - no abstract available

From the commencement of European settlement onward, numerous levelling surveys have been made in Australia on various datums, and although professional surveyors from time to time advocated a national height datum based on mean sea level, no active move toward a national system of levels was undertaken until after the creation of a National Mapping Council in 1945.

No abstract available

This Bulletin describes the sequence of conodont species in the early Ordovician sediments of the Bonaparte Gulf Basin and the Daly River Basin, northwestern Australia (Fig. 1). The assemblage zones erected by Druce, Jones (1971) for the Lower Ordovician (Tremadocian) of western Queensland are recognized in the Bonaparte Gulf Basin. They are used to correlate the Lower Ordovician sediments both within the Bonaparte Gulf Basin, and between it, the Daly River Basin, and western Queensland. Intercontinental correlations are made on the basis conodonts previously described from Asia, North America, and Europe.

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.

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.