Late Palaeozoic and Mesozoic Epi-Cratonic Sedimentation
Late Carboniferous to Early Permian (300-285? Ma):glaciation and marine sedimentation
MacFarlane Syenite, part of the Triassic Mount Leinster Igneous Complex of eastern Victoria.
At this time the Australian portion of Gondwana lay near the South Pole and had a glacial climate. Glacial deposits are widespread across southern Victoria, especially at Bacchus Marsh and east of Bendigo. They consist of tillite, slump deposits and sandstone and siltstone (Wild Duck Formation and Boorhaman Conglomerate) deposited by glaciers and periglacial and sub-glacial streams, probably in a glaciomarine environment. Striated pavements show that ice movement was mainly towards the north. Marine conglomerates occurring as far south as Bacchus Marsh suggest that a substantial part of the tillites may have been deposited in shallow marine conditions. The Urana Formation, occurring in the subsurface in north-central Victoria, is entirely marine, deposited in quiet, anoxic water.
Triassic (250-205 Ma): rivers and granites
Triassic rocks are of very limited distribution in Victoria. At Council Trench near Bacchus Marsh, a very thin cap of conglomerate, sandstone and mudstone with chopped-up plant fossils is a fluvial deposit. It overlies glaciomarine Permian sediments. In the Benambra region in Eastern Victoria, the Mount Leinster Igneous Complex is scattered over an area of about 350 Km2. It is a suite of alkaline igneous rocks consisting of trachyte, volcaniclastics, volcanogenic sediments, syenites and porphyritic granites. The Teapot Creek Formation represents the remains of a once extensive sheet of volcanics which was deposited onto the Triassic land surface. This was subsequently intruded by a number of high level syenite and granite porphyry bodies. Apart from being within-plate intrusions, the tectonic setting of these rocks is poorly understood. Perhaps they herald the extension and subsequent breakup of Gondwana.