OFR 151.pdf - CRC LEME

Dettmann et al. (1992) have argued that the trend reflects the colonisation of emergent areas
by fern heath and swamp communities as the sea retreated from the Eromanga-Surat Seaway
during the latest Aptian-Albian. If correct, then the link with climate is an indirect one. A
complicating factor is that the Wyandra-1 data also show simultaneous increases in marine
dinoflagellates, Gleicheniaceae and Sphagnum curves during the Early Aptian. A notunlikely
explanation is that other suitable habits for fern-dominated communities were created
by the progradation of deltas during times of high relative sea level. Sphagnum bog
development is likely to have been promoted by low mean temperatures (reducing water
losses by evapo-transpiration) as well as by the high humidity. The expansion of primitive
angiosperms within fern heath communities during the Albian is seen to be a consequence of
marine regression exposing large open areas of mineral soils around the margins of the inland
basins (Dettmann et al ibid.).
Inferred climate
Burger (1988, 1990) has proposed that climates were relatively constant (cool humid)
throughout the Aptian but suggests that the rapidly diversifying tricolpate pollen flora is
consistent with global warming during the Early Albian. Conversely the high relative
abundances of Sphagnum are more consistent with geological evidence for seasonally cold
(microtherm range) and effectively very wet (perhumid) conditions throughout Aptian-Albian
time (see below).
2.2.4 South-West Australia
1. Perth Basin
The stratigraphic correlation proposed by Backhouse (1988) indicates that only the
assemblages recovered from the top of the Leederville Formation are likely to represent
Aptian time. These assemblages imply two distinctive vegetation types were present around
the basin. These are: (1) mixed cheirolepidiacean conifer woodland and Austral Conifer
Forest, dominated by podocarps (Microcachrys) and araucarians (Araucariacites,
Balmeiopsis), which occupied uplands on the landward margin of the basin, and (2) fern
swamp communities dominated by Cyatheaceae, Dicksoniaceae, Matoniaceae and
Schizaeaceae, which grew in the coastal lowlands. Albian microfloras are dominated by
pollen of the brachyphyll araucarian Hoegisporis.
Inferred climate
Climates are suggested to have been humid at low elevations whilst seasonally drier climates
may have prevailed in adjacent uplands, assuming the ecological preferences of the
Cheirolepidaceae have been correctly interpreted (Backhouse 1988). The relatively low
palaeolatitude (~50 0 S) implies temperatures were mild (lower mesotherm) whilst winter
photoperiods are unlikely to have limited plant growth.
2.2.5 Central southern Australia
1. Duntroon Basin
Data provided by Morgan (1986a) and Morgan and Hooker (1993a, 1993b) indicate little
change in the relative abundance of commonly occurring taxa between Necomian and Early
Albian time. Anemia (Cicatricosisporites/Ruffordiaspora) spores become common (up to
25%) during the early Late Albian. Fern spores, especially Cyatheaceae (Cyathidites), are
more abundant than gymnosperm pollen during the latest Albian (and Cenomanian).
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