THE DEVONIAN OF WESTERN AND CENTRAL AUSTRALIA

Abstract

The Devonian of Western and Central Australia consists of sedimentary rocks deposited in intracratonic basins. No igneous activity is known. Devonian rocks are scattered over more than one million square miles and fall into three divisions:

5,000 to 10,000 feet of mainly Upper Devonian marine platform limestones and sandstones in the three western basins with laterally equivalent siltstone and shale in the Canning and Bonaparte Gulf Basins;Upper Devonian terrestrial fish-bearing quartz sandstone and associated siltstone and conglomerate in the Amadeus Basin (12,000 feet) and Dulcie (500 feet) and Toko (unknown thickness) synclines; andpoorly known probable Lower and Middle Devonian red-beds and evaporites in the Canning Basin (8,000 feet), barren quartz sandstone in the Amadeus Basin (3,000 feet), and vertebrate-bearing quartz sandstone in the Dulcie (1,500 feet) and Toko (500 feet) synclines.

Except fr the Amadeus Basin, all these rocks are flat-lying to moderately tilted, and high-angle faults are the chief structural elements. Metamorphism is wholly absent except adjacent to major faults. Steep dips in the Devonian of the Amadeus Basin are related to folding. The rocks of the first division represent part of a depositional phase which continues into the Lower Carboniferous; divisions (ii) and (iii) are probably the end phases of depositional cycles which started before the Devonian.

Interesting features of these rocks are the well-exposed and essentially undeformed carbonate reef complexes of the northern Canning Basin and the Bonaparte Gulf Basin, the thick Frasnian sandstones of the Bonaparte Gulf Basin, and the thick redbed-evaporite sequence of the southern Canning Basin. The reef complexes with their associated basinal facies provide prospects for petroleum production.