CHAPTER 4 - The Silurian System

Abstract

This chapter provides an overview of the Silurian system. Apart from relatively minor occurrences in the northern part of the Perth Basin and in the Carnarvon Basin, in Western Australia, and rather more widespread occurrences in the Amadeus Basin, the only Silurian rocks on the continent are to be found in the Tasman Orthogeosyncline. The bulk of these outcrop in the southeastern States, though their presence in the subsurface beneath the Mesozoic sediments of the Artesian Basin has been proved by deep exploratory wells in some areas. The sediments in the two Western Australian Basins are limestones, dolomites, and cross-stratified quartzose sandstones, products of deposition in broad shallow-water basins with margins of low relief. The Amadeus Basin was receiving only terrestrial sediments. In the Lachlan Geosyncline, the pattern of arches and troughs had been greatly modified during the Benambran Orogeny, the only structures that retained their characters being the Molong–Canberra High and the Melbourne Trough. Following this deformation, there was extensive acid and intermediate volcanism that seems to have been largely restricted to the deformed areas.