Permian coals of Eastern Australia

An overview of the Permian coals and coal bearing basins of eastern Australia is presented. The report is unusually large because it covers an enormous area equivalent to the Carboniferous coal basins of Europe from Scotland, through France, Germany and Poland, to the western Soviet Union. The report contains two major data-bases (see microfiches in vol. 1). The BMR data-base covers the stratigraphy and structure of the basins between the coast and the middle of the Great Artesian Basin, and between Cape York and Tasmania. The CSIRO data-base deals with the properties of the coals in these basins. The databases are summarised in 42 plates (vol. 2) and dozens of line drawings showing surface and under ground geology, stratigraphy, sedimentology and structure, and the chemical and petrographic properties of the coals. T h e illustrations are described and discussed in the text. Three tectonic groups of basins exist: (1) small rifts and valleys with seams u p to 30 m thick; (2)large interior intracratonic basins, with histories comparable to the North Sea and West Siberia Basins, e.g., the Cooper and Galilee Basins, which formed on an early Palaeozoic orogen, were filled by mainly non-marine sediments and coals (over 3 x 101 2 tonnes, but not yet mined), and were then covered by the Mesozoic Great Artesian Basin; and (3) marginal basins, so-called because they formed near the Permian coast of Australia. In the last group, the Sydney-Bowen Basin, which contains almost all of the major black coal mines, was 1700 km long, sub-parallel to the present east coast, and was separated from the palaeo-Pacific Ocean only by a ridge in the developing Palaeozoic and Mesozoic New England-Yarrol Orogen. The basin is thought to have been a foredeep to the orogen, and was possibly also a marginal basin formed over a strike-slip fault system at the western edge of the orogen. The interior and marginal basins have basal, middle, and upper coal measures, which are separated in the interior basins by lacustrine sediments and in the marginal basins by marine sediments. An ice sheet, reaching its maximum in the Early Permian, extended from Antarctica to the southern quarter of Australia. Periglacial conditions occurred farther north but moved southwards as the ice waned in the late Permian, being succeeded by cold-temperate conditions resulting in the widespread upper coal measures. In the marginal basins they were deposited in prograding sedimentary environments, ranging from alluvial fan through fluvial to deltaic, but were subject to marine incursions (one eustatic), and some deformation. They also received a large volume of volcanogenic sediments from major igneous centres in the orogen. With higher and more stable palaeo-water tables, and faster deposition, the marginal basins generally have coarsely banded coals, rich in vitrinite and with high semifusinite ratios. The interior basins had lower water tables and slower deposition and tend to have finely banded coals, low in vitrinite and with low semifusinite ratios. High sulphur, as usual, is related to marine influences. Coal rank is a matter that has received much attention, in part because of its significance in petroleum exploration. It can be correlated directly with palaeo-temperatures in the basins, and indirectly with depths of burial which, in turn, were controlled by Permian tectonic events, and by several Mesozoic and Cainozoic episodes of folding, faulting and igneous activity. Some of these events were more localised than others, but the rank changes are regular and systematic.

Tags: AU, Bulletin, Earth Sciences, GA Publication, Published_External, geology, stratigraphy, structural geology
Organization: Geoscience Australia Data