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salinity, the rest of the marine area being brackish (Banks & Clarke, 1987). Tasmania
then lay in an ennbayment with the western side formed by the northern Victoria Land
sector of Antarctica, which, because no contemporaneous sediments occur there
(Barrett & others, 1986), was probably erosional land. Brackish conditions would have
come about by the influx of fresh water into the restricted bay. Ice-rafted debris, some
up to 2 m across, were still being dropped in, perhaps by pack ice. Littoral deposits
formed in places around the shores of the gulf. A high proportion of silicic tuff in the
upper part of the sequence 30 km south of Hobart testifies to some local volcanism.
The large deltaic complexes in the Bonaparte Basin and Fitzroy Trough point to
considerable erosion in the central Australian hinterland, but this is not shown on the
map because the exact location of eroding areas is uncertain, and at least one
intermontane basin is known from the region. The eustatic fall in sea level intimates
that the Scott Plateau area may have been subaerial once more, and probably
remained so for the rest of the Permian.
PERMIAN 7: LATE TATARIAN (248 -250 Ma)
The last Permian time slice, of but short duration, represents the culmination of the
Late Permian progradation, when very few marine domains were left within the present
day coastlines. It was characterized by the most widespread coal deposition the
continent has ever known, for every non-marine basin from Cape York to Tasmania
and across to Perth was storing up coal (Harrington & Brake!, 1989; Brakel &
Totterdell, 1988). The base of the interval is defined as the base of the economically
important Newcastle Coal Measures, which corresponds to the recession of the
aforementioned short-term eustatic marine incursion. The top of the Permian is taken
as the top of the Protohaploxypinus reticulatus palynozone and its equivalents. A U-Pb
zircon date of 256 ± 4 Ma from near the top of the Newcastle Coal Measures (Gulson
& others, 1990) would make the time slice somewhat older than the dates intimated
by the Harland & others (1982) scale.
After the eustatic interruption, the subsiding Sydney-Bowen foredeep was again
overwhelmed by detritus shed from actively rising highs in the orogen to the east, and
to a lesser extent from westerly sources. The Sydney Basin was at first occupied by
deltaic peatlands, but with continuing southerly progradation alluvial fans advanced
into the depositional site from the north and northeast (Brakel, 1989a). In the northern
proximal areas, raised peat bogs formed on the fan surfaces during quiescent periods,
leading to coal seams becoming sandwiched between thick conglomerates. Large
volumes of tuff were contributed to the Newcastle and Wollombi Coal Measures,
mostly from volcanic centres along the Northumberland Ridge to the east. One
eruption took the form of a Mt. St. Helens - type laterally directed blast, which
devastated a forest and laid out the tree trunks in an ENE-WSW orientation, with a
thick blanket of volcanic ash completely overwhelming the peat swamp in which the
trees were growing (Diessel, 1985). The climate was still cold temperate (Riek, 1972).
The coal measures were succeeded by braided fluvials of the basal Narrabeen Group,
but some reports of glauconite and foraminifera near their mutual boundary suggest
a short-lived interlude of marine influence between the two units, at least locally. The
Gunnedah Basin, upstream from the Sydney Basin, exhibits a similar depositional
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