Abstract
New information from a deep offshore well at Ashmore Reef and from offshore seismic reflection surveys in the Timor Sea shows a total composite thickness of about 50,000 ft. (15,240 m) of Phanerozoic sediments in the Bonaparte Gulf Basin. The stratigraphic similarity between the Permian to early Middle Miocene sequences of the Carnarvon Basin, Ashmore Reef area, and east Timor seems to indicate that these areas consistently lay at the edge of the Australian continent. In Timor, this similarity has been hitherto overlooked because of geologically superficial effects brought about by the Mid-Miocene diastrophism and by subsequent events. Timor and the other Lesser Sunda Islands were deformed possibly because they were situated at the edge of the Australian continent facing Asia, whereas Ashmore Reef and the Carnarvon Basin faced on the Indian Ocean. The offshore seismic reflection surveys reveal that the Sahul shelf has evolved from a Palaeizoic depositional basin with structural axes trending northwestward to a Tertiary basin with axes trending northeastward. The interaction of these two trends is reflected today in the bathymetry of the shelf. The palaeogeography back to the Permian is shown in a series of maps.
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