II II II II II - Geoscience Australia

the map), perhaps being joined by coalescing ice streams descending from the higher
topography, but if precipitation was inadequate, only scattered valley glaciers may
have been possible here, as in New South Wales. In SE South Australia, a marine
connection existed between the Murray infrabasinal area and the sea beyond. During
the coldest periods, a floating ice shelf was probably established over this water, to
connect the glacial lobes of Victoria and South Australia, but in warmer times an open
seaway may have been present, except for a cover of seasonal winter ice.
Meanwhile, western Tasmania experienced an invasion of ice from the west, but the
flow was deflected to the northeast and southeast by a number of monadnocks. The
glacial sheet met the sea in central Tasmania, giving rise to another floating ice shelf.
Islands to the east bore only small ice caps.
Clearly, the ice encroaching onto Tasmania, Victoria, and South Australia radiated out
from a centre in northern Victoria Land, in adjacent Antarctica. To do so, it had to
pass over marine passages lying across its path. Its access to South Australia was
via a rather narrow neck, which may have been wider than shown if it is assumed that
any glaciation on the Yorke and Eyre Peninsulas left no trace of its presence.
Nevertheless, the broad expanse of this lobe compared to its constricted southern
connection strongly implies additional nourishment of this sheet by precipitation.
The eastern seabord region of the continent developed only minor valley glaciers.
Carboniferous palfflochannels cut to over 200 m deep in the southern Sydney Basin
have been interpreted as glacially carved by Herbert (1972), and glaciers may still have
occupied the heads of these valleys at the start of the Permian, supplying coarse
glaciofluvial debris downstream. The "late upper marine" (Kungurian) glacial valleys
described by Dulhunty (1964) may have been first cut by ice at this time (to be reoccupied
by glaciers in the Kungurian), and a glacial moraine on the northern rim of
the basin has been claimed by Dickins & Sutherland (1979). However, there is no
evidence of glaciation in the nearby Gloucester Basin.
Contemporaneous sediments in Queensland's Galilee Basin have been interpreted as
glacigene in part, and derived from alpine glaciers in highlands to the east and north
(Crowell & Frakes, 1971; Hawkins, 1978). Local ice developments may have existed
as far north as the Gulf of Carpentaria, where subsurface diamictite has been
intersected in the Burketown Depression (Meyers, 1969). Dating of this rock has been
frustrated by the complete absence of fossils, and because it overlies a Cambrian
carbonate, it has been considered by some to be part of the Cambrian sequence.
However, there is no evidence of glaciation in Australia during the Cambrian, and we
agree with Burgess (1984) that the lithology is more likely to represent a Permian tillite.
Both the glacier shown in the southeastern lobe of the Burketown Depression, and the
fluvial environment in the rest of the depression, are speculative. The presence of
glacial ice elsewhere in northern Australia is conjectural.
By the end of the time interval, most of the ice had withdrawn from Australia, leaving
retreat sequences behind in places. An extensive example of such a sequence is
found in the Officer Basin, where glaciofluvial deposits overlie the basal tillite; the
palocurrents shown on the map (from Jackson & van de Graaff, 1981a) refer to this
post-glacial condition. Notable following the departure of the ice from the marine
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