OFR 151.pdf - CRC LEME

Inferred climate
The combined data indicate that Aptian to possible Early Albian climates were very wet
(perhumid) and strongly seasonal, with temperatures possibly falling below freezing during
winter months (cf. Rich et al. 1988, Dettmann et al. 1992).
2. Early to Late Albian
The Aptian/Albian (Zone C/D) boundary is marked by the disappearance of several major
plant groups, which had been present in Australia since the Jurassic, such as pteridosperms
(including Pentoxylales), sphenopsids and, possibly bennettitaleans. Gymnosperms
(Araucariaceae, Podocarpaceae, Taxodiaceae) continued to dominate Albian (Zone D) forests
and woodlands, but many of the more prominent species were different from those recorded
in the Aptian (cf. Cantrill 1991). For example the prominent species Gingkoes australis was
replaced by ginkgophyte with smaller leaves. Osmundaceae appear to have been a common
ground cover based on the high relative abundance of their fronds. Angiosperms, were
present but uncommon.
Inferred climate
Floristic change within the Albian is suggested to reflect a high level of environmental
disturbance caused by fluctuating sea level, and tectonic or volcanic activity (Gledow and
Duddy 1981, Douglas 1986). Cantrill and Douglas (1988) interpret fungi associated with the
conifer roots as evidence for nutrient-deficient soils. Climates are interpreted as wet
(perhumid) and cool-cold (microtherm range) due to the high palaeolatitude. These
palaeotemperature inferences are supported by isotopic data (Gregory et al. 1989) which
indicate mean annual temperatures in the catchments of rivers flowing into the Otway and
Gippsland Basins were less than 5 0 C (lower microtherm) and possibly below freezing.
2.2 Microfloras
Marked differences exist in the composition of Aptian-Albian microfloras in the palaeosouthwestern
(~Victoria) and palaeo-eastern (~Queensland) regions of the continent. These
may reflect differences in topography, edaphic conditions and/or depositional regimes, as well
as differences in climate (Dettmann et al. 1992).
Correlation of these microfloras with assemblages on the palaeo-northern margin (~Western
Australia) is difficult due to absence of a number of biostratigraphically useful species in the
latter region (Backhouse 1988, Burger 1994).
2.2.1 North-West Australia
Range data (Helby et al. 1987) indicate that a number of phytogeographically significant taxa
entered Australia during Late Aptian-Albian time. Examples include a brachyphyll
araucarian (Hoegisporis), and several cryptogams. The latter include Cyatheacidites tectifera
whose NLR (Lophosoria) is restricted to cool temperate habitats in South America, Plicatella
(al. Appendicisporites) distocarinata whose NLR (Anemia subgen. Anemia) is restricted to
wet tropical habitats, and an extinct clade within the Gleicheniaceae (Clavifera triplex).
Balme (1964) has recorded tricolpate angiosperm pollen in Albian sediments in Western
Australia.
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