6
1 General Review of Permian Sediments in Western Australia
1.3 Wilga Basin
The smaller Wilga Basin is situated 40 km south of the Collie Basin (centred on
33° 6
S latitude; 116.4° E longitude) and is smaller in size. The Permian sequence
in the Wilga Basin starts with tillites at a depth of about 200 m, which are overlain
by coal measures. The entire sequence contains plant microfossils of Sakmarian to
Artinskian age. The Upper Permian is missing in the Wilga Basin.
1.4 South Perth Basin (Sue-1 Bore)
The South Perth Basin is marked by un-interrupted deposition throughout the entire
Permian. The Permian coal measures in S.P.B. are 4653 m thick compared to about
900 m in Collie B bore and about 700 m in Collie D bore. Sakmarian samples in
Sue-1 samples are 120 m thick compared to the 82 m thick tillite deposits in Collie
B bore, and 12 m thick tillites in Collie C bore.
The Artinskian biostratigraphic units II and III are represented more or less
equally in all Collie-Muja basin bores (Fig. 1.2). On the other hand, unit IV of Upper
Permian age is represented in a diminished thickness in Collie Basin compared to
the accumulation of around 2000 m in Perth Basin. This supports the Darling fault
becoming active around the end of the Artinskian–early Upper Permian.
1.4.1 The Coals of the Collie–Wilga and Perth Basins
The coal samples of the present study were generally rich in exinites supplying
the abundant pollen/spores; vitrinite/inertinite ratios varied. Generally, the coals are
seen as inertinite-rich and vitrinite-poor. The samples usually displayed thin vitrite
layers alternating with thick inertite/fusite layers. The high ratio of inertinite/fusinite
relative to vitrinite in all Permian Gondwana coals has been traced to the climate at the
time, which was wet and cool in summer and freezing in winter. Oxidation through
freeze-drying of the organic matter led to the development of inertinite/fusinite.
The inertinite-abundant dull coals or durains were particularly rich in
pollen/spores. The latter due to their lipid-dominated composition are significantly
more resistant to degradation and oxidation than woody remains. Bright coals, vitrains dominated by the maceral vitrinite, were poor or often devoid of spores/pollen.
On the other hand, some vitrinite-rich coals were found to be exceptionally high in
acritarchs, supporting a water body, and higher water table at times.
The pollen and spore exines belong to the macerals of the Liptinite group that
originates from H-rich lipidic (oily) plant material. The liptinites are relatively stable
and therefore are resistant to biodegradation; hence they preserve in sediments, and
are useful in reconstructing ancient climates and vegetation. Liptinites when observed
1 General Review of Permian Sediments in Western Australia
1.3 Wilga Basin
The smaller Wilga Basin is situated 40 km south of the Collie Basin (centred on
33° 6
S latitude; 116.4° E longitude) and is smaller in size. The Permian sequence
in the Wilga Basin starts with tillites at a depth of about 200 m, which are overlain
by coal measures. The entire sequence contains plant microfossils of Sakmarian to
Artinskian age. The Upper Permian is missing in the Wilga Basin.
1.4 South Perth Basin (Sue-1 Bore)
The South Perth Basin is marked by un-interrupted deposition throughout the entire
Permian. The Permian coal measures in S.P.B. are 4653 m thick compared to about
900 m in Collie B bore and about 700 m in Collie D bore. Sakmarian samples in
Sue-1 samples are 120 m thick compared to the 82 m thick tillite deposits in Collie
B bore, and 12 m thick tillites in Collie C bore.
The Artinskian biostratigraphic units II and III are represented more or less
equally in all Collie-Muja basin bores (Fig. 1.2). On the other hand, unit IV of Upper
Permian age is represented in a diminished thickness in Collie Basin compared to
the accumulation of around 2000 m in Perth Basin. This supports the Darling fault
becoming active around the end of the Artinskian–early Upper Permian.
1.4.1 The Coals of the Collie–Wilga and Perth Basins
The coal samples of the present study were generally rich in exinites supplying
the abundant pollen/spores; vitrinite/inertinite ratios varied. Generally, the coals are
seen as inertinite-rich and vitrinite-poor. The samples usually displayed thin vitrite
layers alternating with thick inertite/fusite layers. The high ratio of inertinite/fusinite
relative to vitrinite in all Permian Gondwana coals has been traced to the climate at the
time, which was wet and cool in summer and freezing in winter. Oxidation through
freeze-drying of the organic matter led to the development of inertinite/fusinite.
The inertinite-abundant dull coals or durains were particularly rich in
pollen/spores. The latter due to their lipid-dominated composition are significantly
more resistant to degradation and oxidation than woody remains. Bright coals, vitrains dominated by the maceral vitrinite, were poor or often devoid of spores/pollen.
On the other hand, some vitrinite-rich coals were found to be exceptionally high in
acritarchs, supporting a water body, and higher water table at times.
The pollen and spore exines belong to the macerals of the Liptinite group that
originates from H-rich lipidic (oily) plant material. The liptinites are relatively stable
and therefore are resistant to biodegradation; hence they preserve in sediments, and
are useful in reconstructing ancient climates and vegetation. Liptinites when observed