II II II II II - Geoscience Australia

portion of Tasmania was the sporadic development across the north of the state of a
2 metre-thick nearshore Tasmanites oil shale.
Non-glaciated Regions
Apart from the great ice sheets, the most conspicuous feature of the continent during
Permian 1 was a 1800 km-long volcanic belt parallel to the east coast and stretching
from the Sydney Basin to Townsville. It consists of bimodal volcanics which, under
the Sydney Basin, form a pile at least 8.6 km thick (Qureshi, 1984). Between the
outcrops of the Boggabri Volcanics in the Gunnedah Basin and the Camboon Andesite
in the Bowen Basin, the eruptives are known from numerous petroleum and coal
exploration drill holes, and from their geophysical expression as the Meandarra Gravity
Ridge. With contemporaneous activity taking place northeast of Newcastle, north of
Mackay, and west of Cairns, the volcanism spanned a total length of about 2200 km.
Termed the Ayr Volcanic Rift by Scheibner (1976), it was attributed to rifting in front of
a subduction zone lying off the east coast. However, the Cannboon Andesite and
equivalents appear to represent a short-lived volcanic arc coincident with the earlier
Devonian - Carboniferous Connors - Auburn Arc (Day & others, 1983), while the suite
of volcanics to its west and south can be accounted for by back-arc extension.
A subduction complex existed in eastern New England in the Late Carboniferous, but
was terminated in the Early Permian, when tectonic movement changed from
essentially convergent to dominantly strike-slip (Cawood, 1982b). Deep-water
sediments collected in the region; they contain basalt occurrences of mid-ocean ridge
character, although this does not necessarily mean that a spreading centre formed
locally. The basic volcanics may have been associated with the earliest stages of
rifting which never proceeded to the sea-floor spreading stage (Leitch & Asthana,
1985; Scheibner & Pearce, 1978). Korsch (1982) suggested that one of the basalts
possibly represents a seannount.
In the Gympie Terrane, the sediment types at the start of the Permian are also
indicative of a deep oceanic setting (Day & others, 1983), but the subsequent
dominantly andesitic Highbury Volcanics are amygdaloidal (Runnegar & Ferguson,
1969), signifying lower water pressures and shallower depths, with chemical evidence
pointing to eruption in an intra-oceanic arc (Cranfield & Murray, 1989). The terrane
itself is allochthonous, being located at the time an unspecified distance to the east in
the Eopacific and attached to similar terrane, part of which now occurs in New Zealand
(Harrington, 1983; Waterhouse & SiveII, 1987).
Shallow marine environments in Queensland are represented by the clastic Burnett
Formation of the Yarrol Basin, and parts of the Rannes and Carmila beds of the
Gogango Folded Zone. The latter domain received appreciable ashfalls from nearby
volcanism. A continental shelf presumably existed northwards from these areas to
east of Cape York Peninsula. The Silver Spur beds near the New South Wales border
were also shallow marine. In the Sydney Basin, deposition was beginning with the
marine transgression which laid down the Lochinvar Formation in a cold climate,
accompanied by basaltic volcanism. Eastern Tasmania also experienced cold shallow
marine conditions, except for large island areas which were presumably erosional.
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