Marine geology of the northwest Australian continental shelf

This Bulletin presents the results of a geological reconnaissance of the northwest Australian continental shelf by the Bureau of Mineral Resources carried out during two 3-month cruises, one in late 1967 and the second in late 1968. In compilation of the results some use has also been made of the shallow seismic reflection profiles and echograms collected during a marine geophysical survey of the Northwest Shelf by Ray Geophysical Division of Mandrel Industries Inc. under contract to the BMR in 1968. The other main sources of data used are the published and unpublished soundings compiled by the RAN Hydrographic Office, and the sea-bed sediment notations on Australian and British Admiralty Charts. The brief description of the offshore structural framework and Phanerozoic sedimentation is almost entirely based on the subsidized petroleum exploration work of BOC of Australia Ltd and associated companies; it does not include results obtained after 1971. The region surveyed extends from Barrow Island in the south to beyond Scott Reef, a distance of 1200 km (Fig. 1). It covers the Rowley Shelf and the southern part of the Sahul Shelf, as defined by Fairbridge (1953); in popular usage all this wide area is now referred to as the Northwest Shelf, and this term is preferred here. The basic objectives of the survey were to describe the sediments of the continental shelf and upper slope and to map their distribution, and to elucidate the late Cainozoic geological history of the continental margin from the study of surface morphology and shallow structures. The Northwest Shelf was chosen because of its position on the west side of the continent, and because the limited data available on ocean water chemistry and circulation patterns indicated that some potential for deposits of phosphate existed. Although sediments enriched with phosphorus were encountered locally, no material approaching economic grade was recovered.