II II II II II - Geoscience Australia

Fitzroy Tough underwent subsidence instead, to become the locus of a barrier -
lagoonal complex, mostly with fringing deltas in the southeast, and very shallow marine
water to the northwest.
The Wagina Sandstone of the northern Perth Basin denotes marine regression in this
area, as it records continental to paralic environments, including coal swamps
(Playford & others, 1976). Coal-prone fluvial aggradation remained the feature of the
Collie and southern Perth Basins, and appeared for the first time in the Oaklands Basin
of southern New South Wales.
The main erosional terrains of the continent were little changed in broad aspect from
Permian 4 times.
PERMIAN 6: MIDDLE KAZANIAN - MIDDLE TATARIAN (250-256 Ma)
Although many marine areas continued as such, the Permian 6 interval witnessed the
start of the general progradation that characterized the rest of the Permian and the
Triassic, when non-marine and paralic depositional sites increased at the expense of
marine ones. The development of large progradational complexes on both sides of
the continent, except where local tectonics determined otherwise, points to a eustatic
drop in sea level as the common cause. The base of the time slice is set at the
beginning of the regression in the Sydney and Gunnedah Basins (which allowed the
deposition of the important upper coal measures succession in eastern Australia); it
also corresponds to the beginning of regression in the Bonaparte Basin, and
approximately to the change from marine to non-marine/paralic in the Cressbrook-
Buaraba Block of southeastern Queensland. The 250 to —256 Ma date of the interval
is based on K-Ar dating of latites at the base of the Illawarra Coal Measures and the
Harland & others (1982) time scale, but as noted previously, if a U-Pb zircon date of
266 ± 0.4 Ma from the middle of the Tomago Coal Measures by Gulson & others
(1990) is confirmed, this time slice would be considerably older.
The Sydney and Gunnedah Basins filled with deltaic and fluvial coal measures, as
clastics poured in from adjacent uplifted areas in New England, and to a lesser extent
from the western Lachlan highlands. The major anticlines in the northern Sydney
Basin were also active. The main progradation direction was southerly along the basin
axes, but most detritus was introduced into the depositional system from the sides via
alluvial fans. Early in the interval, subsidence of the eastern parts of the basins briefly
admitted the sea (the Kulnura Marine Tongue and equivalents), and promoted the
growth of an extensive alluvial fan apron along the western margins (Marangaroo
Conglomerate) (Brakel, 1984 ; Havord & others, 1984; Hunt & others, 1986).
Another marine incursion (Dempsey Formation and equivalents), this time eustatic in
nature (Brake!, 1986), marked the end of the time slice.
Volcanoes were active in the southeastern Sydney Basin at the start of the interval (the
Gerringong latitic eruptions). Later, felsic volcanism began further north on the eastern
side of the basin off Newcastle, contributing tuffs to the Tomago Coal Measures, and
one of these tuffs, the Thornton Claystone, originated in a lateral blast eruption which
devastated a forest and laid out the tree truncks in a NE-SW orientation (Diessel &
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