Exploration Geophysics - Volume 5, Issue 4, 1974

The Western Coral Sea region contains one major and three minor marginal plateaux, partly surrounding a deep abyssal plain. The Coral Sea Abyssal Plain is underlain by about 1 km sediment and oceanic crust generated by an early Eocene seafloor spreading phase. The large Queensland Plateau consists of subsided continental crust with basement rocks of Palaeozoic age which are tectonically part of the onshore Tasman Geosyncline.

Graben, or continental rift features occur beneath the Queensland Trough, and beneath the plateau/ basin margin. Here 1-3 kms of probable Upper Cretaceous “rift valley” sediments overlie basement. Subsidence of the plateaux followed seafloor spreading in the basin and marked the onset of “post-break up” sedimentation. Lo’ws in the plateau basement are infilled by Eocene sediments, while changing ocean current patterns gave rise to an Oligocene depositional break. Residual plateau highs along old Palaeozoic trends subsided in the early Miocene and are locally capped by modern coral reefs.

In certain circumstances magnetic fields are contaminated by noise whose autocorrelation functions may be estimated. Least squares Wiener filters may be designed to effect transformations of the magnetic fields so that an optimum suppression of the autocorrelated noise is achieved.

Statistical studies of a computerised automatic interpretation technique based on the method of Koulomzine et al (1970) are extended to the evaluation of the dip parameter for semi-finite magnetized dykes. Results show that dip estimates are in general very good (within 5%) with some deterioration in accuracy for small depth to width ratios on more asymmetric anomaly shapes.

The so called resistivity gradient array, described by Whiteley (1973) and illustrated in figure 1, presents a unique opportunity for the application of semi-quantitative interpretation techniques based on potential theory. Large current electrode separations, as encountered in the resistivity gradient array, enable the applied potential field in the vicinity of the centre of the array to be closely approximated by a constant field (Kunetz, 1966). The assumption of a constant applied field considerably reduces the complexity of mathematical treatment.

The Physics Department of the University of Newcastle has owned and operated a Daedalus (USA) airborne thermal infrared line scanner for the past 4 years. Most of the work, which has ranged over the eastern half of Australia, New Guinea and Bouganville, has utilised the 8-14/µm waveband. A 3-5/µm detector can be interchanged with the longer band width detector, but because the 3-5 band is likely to pick up some reflected solar radiation, whereas the 8-14 band gives almost pure earth radiated energy, the latter has been found more generally useful.