L061 St George-Eulo seismic reflection and refraction survey, Great Artesian Basin, QLD, 1962

A seismic aluvey was made between St George and the Queensland/South Australia border in the latter half of 1962. The results of the part of the survey over the Surat Basin, the Nebina Ridge, and the Eulo Shelf are presented in this Record. The survey aimed at providing information on the nature and structure,of the rocks underlying the Mesozoic sediments of the Great Artesian Basin, in particular across the Nebine Ridge and Eulo Shelf. The results of the survey between St George and Bollon indicated a sedimentary section of the order of 5000 ft overlying a basement rock of either metamorphic or igneous origin. The-deepest section recorded was of about 5700 ft, about 12 miles west of St George and probably corresponds to the Boolba Trough suggested by Jenkins (1958). The sedimentary section becomes gradually thinner westward as the Nebine Ridge is approached and about 3000 ft of sediments were recorded about ten miles west of Bollon. A reflection traverse northwards along the axis of the Boolba Trough indicated a thinning of sedimentary section of about 40 ft per mile. No structural explanation for a magnetic lineament interpreted from aeromagnetic work was found. Velocities of over 19,000 ft/s were recorded from granitic rocks at shallow depths over the Nebine Ridge. A velocity of 19,500 ft's was measured close to a granite outcrop at Eulo. A thickening of the sedimentary section between the Eulo Shelf and Nebine Ridge was confirmed by refraction shooting and depths indicated that the total section (3300 ft) was not significantly greater than the depth of the water bores. No apparent development of the trough to the north or west was indicated.