II II II II II - Geoscience Australia

Of the erosional areas not already mentioned, those shown for the Cape York
Peninsula region and western New England are postulated on the basis of intruding
plutons probably being accompanied by uplift. The New England high was the likely
source of the conglomerates in the Temi Group.
PERMIAN 2: EARLY - MIDDLE SAKMARIAN (277-271 Ma)
This time slice is essentially a deglaciated version of Permian 1. The only ice
remaining was in the form of localised valley glaciers in northern Victoria, and in the
Oakover Valley area on the southern Canning Basin margin; the glacigene deposits
in both places have been dated by palynology.
As sea level rose because of the melting of the ice caps, marine transgressions
occurred in southern Victoria, Tasmania, the eastern Murray infrabasinal area (to the
Oaklands Basin), and the Bonaparte, Carnarvon, northern Perth, and Temi Basins, and
to a lesser extent in the Sydney Basin. But in the Canning and Arckaringa Basins the
influx of sediment on their northeastern sides more than kept pace with the rising sea
level, and actually caused the shorelines to prograde. An apron of fluvial and some
lacustrine deposits along the northeastern Canning Basin was fed by an erosional
region to the north, and similarly, a fluvial and deltaic apron along the northeastern
Arckaringa Basin was supplied from highlands to the east. In the Pedirka Basin,
initially low energy, fine-grained fluvials gave way to higher energy sand-dominated
fluvial aggradation by the end of the time interval. This sedimentary influx into the
central Australian basins was probably caused by recycling of glacial detritus left
behind on the land surface, and by increased erosion in highlands rising on the
removal of the ice load. Fission track dating indicates uplift around the northern
Amadeus Basin at 280-260 Ma (Tingate & others, 1986).
The southern Perth Basin was a graben between the Yilgarn Block and "Greater India",
and the site of fluvial peatlands. A significant amount of the sedimentary fill may have
been derived from the adjoining part of Antarctica to the south. A sedimentary basin
occupied a substantial portion of the southwestern Yilgarn Block, but now only
remnants such as the Collie Basin remain (Wilson, 1989). Apart from the Naturaliste
Plateau and the Leeuwin Block, the land shown west of the Perth Basin was rifted
away when India and Australia separated in the Early Cretaceous. The northern Perth
Basin and the Carnarvon Basin comprised a cold-water marine gulf, which only
supported a fauna of low diversity. Most of the Canning Basin, as well as the
Bonaparte Basin, experienced shallow marine conditions. The environment prevailing
over the Scott Plateau area at this time is conjectural.
Seismic sections in the Arafura Basin show a substantial thickness of sediments
between the sub-Jurassic unconformity and the youngest Palmozoic (palynological
Stage 2) found by drilling. This undrilled succession, which itself contains a sequence
boundary, probably spans the entire Permian period, and possibly much of the
Triassic as well. The seismic character of the beds is similar to shallow marine
equivalents in the Bonaparte Basin (J. Bradshaw, BMR, pers. comm.).
The marine sediments at the top of the sequence in the Bacchus Marsh area could
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