The Bureau of Mineral Resources has again'extended its geophysical programme in the search for oil to the continental shelf area of Australia by carrying out a combined gravity, and seismic survey in the Timor Sea/Joseph Bonaparte Gulf area of northwest Australia. The survey investigated the capabilities of the surface marine gravity meter for reconnaissance gravitywork at sea, and the penetration and quality of seismic reflections obtainable using a spark discharge source consisting of an array of electrodes. The possibility of operating the two methods simultaneously was also investigated.
The seismic reflection sections recorded were much better than expected, with good-quality reflections being recorded to 1.6.sec. the gravity meter and seismic'equiPment were operated simultaneously at boat speeds of 8 to 9 miles per hour.
The-seismic results have shown that a large Permian and Mesozoic sedimentary basin exists in the Joseph Bonaparte Gulf and extends to the north and north-west into the Timor Sea. It is an offshore extension of the
Bonaparte Gulf Basin, and contains at least 10,000 feet of post-Permian sediments. .Although the trends of the gravity anomalies agree with the general shape of the basin as defined by the seismic results, a large positive anomaly occupies the central deep part of the basinand does not seem to be related to basement relief.