GEOLOGY OF THE OFF-SHORE AREAS OF NORTH-WESTERN AUSTRALIA

Abstract

CONTOURING of Admiralty Chart No. 475 "North West Coast of Australia with the Off-lying Island and Reefs", 1928-1950, has revealed the existence of a number of offshore ridges along the outer edge of the Australian Continental Shelf. These ridges connect the coastal ranges of Exmouth Gulf in Western Australia with Sahul Banks, opposite Timor. Some of them are very large features and they are separated from the Continental Shelf by pronounced troughs. On the other hand, an even deeper trough separates them from the islands of Timor, Roti and Sawu. Other swells, rising almost to sea level, run parallel with them further out to sea. Geological comparisons are drawn which suggest that a deep stratigraphic section may be present in the general area where these ridges occur. Evidence is also presented to show that these features are tectonically and positively active, whereas the bounding troughs are in process of structural sinking. The size of some of these ridges, which approach the dimensions of the Lesser Sunda Islands, suggest that they are largely submerged and complex folded ranges, of which considerable parts are accessible to exploration. It is shown that these ranges all occur within the boundaries of Teichert's "Westralia Geosyncline". It is suggested that folding, intermediate in in tensity between the Alpine nappes of Timor-Roti and the gently warped sediments of the continental sedimentary basins of Australia, may be present in them.

If so, these somewhat sharper folds may prove to be suitable for considerable accumulation of petroleum, as so often happens in the fore-front folds of other Alpine belts.