Exploration Geophysics - Volume 4, Issue 1, 1973

The effect on stripping factors of the air between aircraft and ground can be determined by counting at various altitudes over pure sources of uranium and thorium. One published set of spectra from a small crystal indicates that stripping factors vary with altitude, and ground determined values are probably too low at 100 metres altitude. The ability of various window systems to separate uranium and thorium series radiation differs, even for identical crystal volumes and ideal conditions. The systems can be compared if complete calibration is available. The narrow window systems are most precise and in addition they offer practical advantages because they are highly specific for the radiation from natural radionuclides.

Offshore reconnaissance seismic sparker surveys shot during the mid-sixties in the Bonaparte Gulf Basin on the Northwest Australian Shelf, outlined a number of diapiric features in the southern part of the Basin. Early aeromagnetic and marine gravity programmes were run on too wide a grid to give clear indications of the nature of the intrus-ives. Later, more sophisticated seismic equipment was used to map the plugs and it became possible to date the age of the movement of the intrusives in several cases. A wildcat well, Sandpiper No. 1 was subsequently drilled on the crest of one of the features; it entered massive salt at a fairly shallow depth, as did another well, Pelican Island No. 1, a hundred miles to the south. Hypotheses involving salt migration toward the Basin margins are put forward to explain the Wickham Gravity High, uplift at the SW Basin Margin Fault and the Petrel Structure. The salt is dated as "probably Devonian" with salt flowage probably continuous from at least Upper Permian time.

The Second International Conference on Geophysics of the Earth and the Oceans was held at Sydney University in January. Over 450 delegates attended the Conference froti all over Australia and from many overseas countries. The undoubted success of this Second Conference has established it as a continuing series of Conferences. A particularly wide range of topics were covered both in the Invited Papers and in the many excellent contributed articles. The rapid development of the field of geophysics was reflected in the introduction of several topics that were not discussed at the First Conference in 1970.