L031 Oodnadatta experimental seismic reflection and refraction survey, SA, 1957

Brief description

In July and August 1957 an experimental seismic survey was done in the Oodnadatta area of the Great Artesian Basin. The purposes of the survey were to find whether reflections could be recorded from beneath duricrust, a siliceous surface deposit, and whether structures mapped by surface geological methods persist with depth. Reflections were recorded from beneath the duricrust using shallow pattern holes and six geophones per trace; the sub-surface structure was mapped with reasonable accuracy. In areas where the duricrust is eroded, reflections of fair quality were obtained using a single shot-hole and six geophones per trace. A seismic reflection traverse across the Oodnadatta anticline indicated that the structure was present in a horizon which corresponds to the top of the artesian aquifer at a depth of about 1000 ft below datum (400 ft above MSL). The seismic results indicated that the anticline was of smaller relief than had been e stimated from surface mapping. There was a change from fair-quality persistent reflections at shallow depths to poor-quality less numerous reflections with sporadic dips at greater depths; this probably represents the base of the Cretaceous. The greatest depth from which Cretaceous sediments were recorded was about 2350 ft below datum. Reflection depths computed by seismic methods correspond closely with lithological boundaries, and in particular the base of the Cretaceous sediments, encountered in the Santos No. 1 bore. The results of a refraction traverse on the crest of the Oudnadatta anticline show the presence of a 'basement' refractor with a velocity of 13,900 ft/sec at a depth of about 1245 ft below datum. There is slight evidence of a refractor with a substantially higher velocity at about twice this depth. The 'basement' velocity of 13,900 ft/sec is consistent with the assumption that there is a pre-Cretaceous layer between the Cretaceous sediments and the Precambrian basement complex.

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Maintenance and Update Frequency: asNeeded

Statement: In July and August 1957 a seismic party from the Bureau of Mineral Resources, Geology and Geophysics made an experimental seismic survey near Oodnadatta, South Australia. Oodnadatta is a small town about 600 miles north of Adelaide on the railway between Port Augusta and Alice Springs. It is on the western margin of the Great Artesian Basin,just within the western limit of the flowing bores. The Oodnadatta artesian bore is 1571 ft deep and, when first drilled, provided a supply of good water which rose 34 ft above the ground surface (Jack, 1915). The seismic work done by the Bureau was requested by Santos Ltd through the Department of Mines, South Australia. Santos Ltd was represented during the survey by the geological and geophysical consulting company; Geosurveys (Aust) Ltd. Mr. J.E. Webb, senior geophysicist of the Department of Mines, visited the seismic party in the field.