THE NGALIA BASIN, NORTHERN TERRITORY — RECENT GEOLOGICAL AND GEOPHYSICAL INFORMATION UPGRADES PETROLEUM PROSPECTS

Abstract

The Ngalia Basin has been the subject of systematic geological and geophysical investigation by the Bureau of Mineral Resources since 1967 and by Magellan Petroleum Australia Ltd. since 1968. The Ngalia Basin is an intracratonic structural depression, containing a small accumulation of late Precambrian and Palaeozoic sediments in the southern part of the Northern Territory. It covers an area of about 6000 sq.mi. and contains shallow marine, glacial and continental rocks of Adelaidean, Cambrian, Ordovician and Carboniferous age. It is asymmetrical in north-south cross-section with the thickest sediments preserved near the faulted northern margin. These sediments can be correlated with those of the prospective Amadeus Basin, but they are yet to be tested for hydrocarbons by exploratory drilling.

Within the basin, where outcrops are sparse, seismic and gravity data provide valuable information pertaining to the depositional and tectonic history. The geological and geophysical studies have upgraded the hydrocarbon potential of the area. Structural traps are thought to exist, particularly in the western part of the basin, associated with folded faults developed over slightly dipping thin thrust plates. Further detailed interpretation of the geophysical results is under way directed towards defining drillable prospects.