3 The Microfloral Assemblages—Their Environmental and Climatic …
107
Biostratigraphic Unit II—The Lower Artinskian is characterised by the dominance of the saccate pollen Sulcatisporites potoniei, and accompanying spores; the
trilete spinate Acanthotriletes and Microbaculispora are also conspicuous members
of this assemblage. Unit II is referred to as Sulcatisporites zone. This assemblage is
found in siltstones and sandstones overlying the tillites. The entire sequence of tillites
and overlying sandstones and siltstones was referred to as the Stockton Formation
(Low 1958). This sequence consists of coal measures, referred to as the Collie Formation or the Lower Coal Measures (Lord 1952). The Collie Coal Measures correspond
to the Irwin River Coal Measures in the northern Perth Basin (Playford 1959). The
latter have been dated as Artinskian (McWhae et al. 1958).
Microbaculispora tentula and Parasaccites gondwanensis dominant in the tillites
of UNIT I decrease in numbers dramatically towards the end of the Sakmarian and
have only a sporadic presence in Zone II; they are overrun by Sulcatisporites potoniei
and Acanthotriletes tereteangulatus. Generally, the microflora in Unit II is richer in
pollen and spore forms than Unit I. Disaccate pollen usually having a very small
isolated appearance in UNIT I increase notably in UNIT II (Appendices B, C, D).
Marsupipollenites is present (Figs. 3.2, 3.3 and 3.4).
Zonate spores such as Kraeuselisporites and Gondispora reach in Collie Basin
26%, smaller numbers in Sue No. 1 bore in the Perth Basin. Zonate spores are
produced today by ferns such as Lycopodium complanatum and Angiopteris as well as
by some species of Selaginella and Asplenium. They can thrive only in wet conditions.
The Lower Artinskian therefore was wet and still cold.
The change in the composition of pollen and spore types in the Sulcatisporites
Zone signifies a change in vegetation which follows a change in climatic conditions.
The changes in the depositional environment as expressed in the vegetation community are recorded by the fossil pollen and spores. The plant community that existed
in UNIT I dominated by the Cordaites and represented by Parasaccites gondwanensis became sparse. Likewise, Punctatisporites gretensis has only a trace presence
in UNIT II. The Cordaites became extinct, and have no representatives in younger
geological formations.
The ‘lowlands’ swamps with varying water level have been taken over by fernlike plants, forming the under story, including pollen of Marsupipollenites and other
spores such as several species of Microbaculispora and spores of Retusotriletes. On
the other hand, Calamites represented by monolete spores such as Laevigatosporites
are horsetails, the major contributors to the coal deposits in the Northern hemisphere,
are also represented in the Collie-Perth Basin, Permian and also in the equivalent zone
of the Lower Gondwana sediments in India (Banarjee and D’Rozario 1990). They
have today a sole representative in the herbaceous Equisetum. Zhuo Feng (2017) in
his reconstruction of the Permian flora in China, based on fossil forests, describes the
Calamites as “fast growing upright, forming bamboo-like thickets and an extensive
prostrate rhizome system.” The rhizome system is reminiscent of today’s mangroves.
In the second half of the Lower Artinskian, water level in the wetlands had risen.
A sign of a change in the climate towards higher rainfall, flooding of lowland and
forming of lakes is evident from the peaks of acritarchs (Figs. 3.2 and 3.3). Peaks in
acritarchs are met with extreme lows in disaccate pollen, including Sulcatisporites
107
Biostratigraphic Unit II—The Lower Artinskian is characterised by the dominance of the saccate pollen Sulcatisporites potoniei, and accompanying spores; the
trilete spinate Acanthotriletes and Microbaculispora are also conspicuous members
of this assemblage. Unit II is referred to as Sulcatisporites zone. This assemblage is
found in siltstones and sandstones overlying the tillites. The entire sequence of tillites
and overlying sandstones and siltstones was referred to as the Stockton Formation
(Low 1958). This sequence consists of coal measures, referred to as the Collie Formation or the Lower Coal Measures (Lord 1952). The Collie Coal Measures correspond
to the Irwin River Coal Measures in the northern Perth Basin (Playford 1959). The
latter have been dated as Artinskian (McWhae et al. 1958).
Microbaculispora tentula and Parasaccites gondwanensis dominant in the tillites
of UNIT I decrease in numbers dramatically towards the end of the Sakmarian and
have only a sporadic presence in Zone II; they are overrun by Sulcatisporites potoniei
and Acanthotriletes tereteangulatus. Generally, the microflora in Unit II is richer in
pollen and spore forms than Unit I. Disaccate pollen usually having a very small
isolated appearance in UNIT I increase notably in UNIT II (Appendices B, C, D).
Marsupipollenites is present (Figs. 3.2, 3.3 and 3.4).
Zonate spores such as Kraeuselisporites and Gondispora reach in Collie Basin
26%, smaller numbers in Sue No. 1 bore in the Perth Basin. Zonate spores are
produced today by ferns such as Lycopodium complanatum and Angiopteris as well as
by some species of Selaginella and Asplenium. They can thrive only in wet conditions.
The Lower Artinskian therefore was wet and still cold.
The change in the composition of pollen and spore types in the Sulcatisporites
Zone signifies a change in vegetation which follows a change in climatic conditions.
The changes in the depositional environment as expressed in the vegetation community are recorded by the fossil pollen and spores. The plant community that existed
in UNIT I dominated by the Cordaites and represented by Parasaccites gondwanensis became sparse. Likewise, Punctatisporites gretensis has only a trace presence
in UNIT II. The Cordaites became extinct, and have no representatives in younger
geological formations.
The ‘lowlands’ swamps with varying water level have been taken over by fernlike plants, forming the under story, including pollen of Marsupipollenites and other
spores such as several species of Microbaculispora and spores of Retusotriletes. On
the other hand, Calamites represented by monolete spores such as Laevigatosporites
are horsetails, the major contributors to the coal deposits in the Northern hemisphere,
are also represented in the Collie-Perth Basin, Permian and also in the equivalent zone
of the Lower Gondwana sediments in India (Banarjee and D’Rozario 1990). They
have today a sole representative in the herbaceous Equisetum. Zhuo Feng (2017) in
his reconstruction of the Permian flora in China, based on fossil forests, describes the
Calamites as “fast growing upright, forming bamboo-like thickets and an extensive
prostrate rhizome system.” The rhizome system is reminiscent of today’s mangroves.
In the second half of the Lower Artinskian, water level in the wetlands had risen.
A sign of a change in the climate towards higher rainfall, flooding of lowland and
forming of lakes is evident from the peaks of acritarchs (Figs. 3.2 and 3.3). Peaks in
acritarchs are met with extreme lows in disaccate pollen, including Sulcatisporites