OFR 151.pdf - CRC LEME

Pteridosperms, cycads, bennettitaleans, ferns and fern allies, including isoetalean lycophytes,
formed the understorey. Necomian macrofossil collections from the Surat Basin indicate
conifers and ginkgophytes formed possibly open forests and woodlands. Here, the
understorey included relations of the horsetails (sphenopsids), as well as pteridosperms, and
ferns.
Inferred climate
The data indicate that conditions were humid. Temperatures are presumed to have been
seasonally cool-cold (microtherm range) due to the relatively high palaeolatitudes and
intraplate location. However the only firm evidence that temperatures fell below freezing
point during winter is geological (see below).
1.1.4 South-West Australia
Abundant Early Cretaceous macrofossils occur in the Collie Basin (Nakina Formation), Perth
Basin (Bullsbrook and Leederville Formations), Carnarvon Basin (Birdrong Sandstone and
Nanutarra Formation), Canning Basin (Broome Sandstone and Callawa Formation) and
Officer Basin (Cronin Sandstone) (references in McLoughlin 1996, McLoughlin and Hill
1996). The age of these formations vary but most pre-date the Aptian (Fig. 2 in McLoughlin
1996). Shared taxa suggest that many of the Western Australian macrofloras are correlatives
of the Necomian (Zone B) macrofloras of southeastern Australia.
Brachyphyll araucarians and podocarps appear to have been the dominant tree taxa.
Subcanopy taxa included bennettitaleans (abundant), pteridosperms, diverse ferns and fern
allies. Ferns included Gleicheniaceae, Osmundaceae and a possible Dipteridaceae (a family
whose one living representative is confined to tropical wet sclerophyll forest in northeastern
Queensland). Fern allies included isoetaleans. The macrofloras differ from those in
southeastern Australia in that ginkgophytes, equisetaleans and bryophytes had become extinct
by the end of the Necomian.
Inferred climate
Climates were humid throughout the region whilst mean temperatures are presumed to have
been relatively warm, possibly lower mesotherm, due to the relatively low palaeolatitude
(~47-50 0 S). Strong seasonal contrasts in climate are indicated by prominent growth rings in
fossilised conifer wood preserved in Carnarvon and Perth Basins. Fungal growth, which also
may have been seasonal, is evident in wood from the Carnarvon Basin (McLoughlin et al.
1995a).
1.1.5 Centra southern Australia
No known record.
1.1.6 South-East Australia
Early Cretaceous floras preserved in the Otway and Gippsland Basins, then located on the
palaeo-western margin, are amongst the best studied in Australia (references in Douglas and
Williams 1982, Douglas 1994).
Macrofossils assigned to the Tithonian-Berriasian (Megafloral Zone A of Douglas 1969) in
the Otway Basin are dominated by bennettitaleans, with sphenopsids forming the understorey.
Significantly, a number of the bennettitalean leaf-forms are not found in coeval Western
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