Wongela GeoIilysical Pty Ltd conducted a helicopter gravity survey for the French Petroleum Company (Australia) Pty Limited in northern South Australia during the period 22nd August to 21st November, 1963, and established 2204 new gravity stations. The area surveyed is in Oil Exploration Licences Nos 20 and 21, and originally covered 34,000 square miles. This area was increased to 35,500 square miles to fill in a gap between the subject survey and the Delhi Alton Downs survey farther east. The work is tied to previous reconnaissance gravity surveys in Central Australia and completes the gravity coverage of the Simpson Desert.
The survey was carried out to determine the extent of Palaeozoic sedimentation in the area and in particular to determine whether Amadeus Basin sediments extend into the survey area. These sediments are masked in the area by relatively flat-lying Mesozoic and more recent sediments. The younger sediments have much the same thickness and density throughout the survey area, and for this reason their contribution to variations in the anomaly field is small. Hence the variations in the anomaly field are thought to be due mainly to density contrasts in the basement and between the basement and pre-Mesozoic sediments.
The survey results have defined some major geological structural units. These are described and discussed individually in the text of the report. Of particular interest is the Dalhousie Gravity Depression which probably represents a large area of pre-Permian sedimentation, about 8000 feet in thickness. To the east of this feature is a platform area which was probably fairly stable and high standing dUring pre-Permian time in which period it received only a thin cover of sediments. It is probable that since early Permian times the area has been depressed relative to the area of the Dalhousie Gravity Depression and the area farther west, and has received extensive Permian and Mesozoic sedimentation, the sediments thickening towards the east.
