OFR 151.pdf - CRC LEME

7.4.2 Palaeobotany
A disproportionate number of the taxa that became extinct at the K/T boundary were
angiosperms, especially Proteaceae characterised by large, highly ornamented pollen. Two
consequences of this during the Danian in southern Australia are: (1) Gymnosperm
populations expanded at the expense of angiosperms rather than cryptogams. (2) Austral
Conifer Forest and fern heath communities were impoverished (floristically simple) relative
to their Maastrichtian predecessors. On present indications, Paleocene forests and/or
woodlands in northern and central Australia were co-dominated by angiosperms and
gymnosperms although the most common canopy species were Cupressaceae and/or
Taxodiaceae and Cunoniaceae, not Podocarpaceae as in southern Australia. Sparganiaceae
(burr reed) swamps, which formed along the northwestern margin and in the centre during the
Late Paleocene, appear to be the first extensive herb-dominated communities to develop in
Australia.
7.4.3 Palaeoclimates
Floristic trends, especially the increased diversity and dominance of angiosperms during the
late Danian and Thanetian, are consistent with increasing global temperatures and (southern
Australia) photoperiods. For example, although ancestral Nothofagus spp. become
sporadically dominant in the south-east, these quasi-temperate rainforest communities usually
included angiosperms and cryptogams whose NLRs are found in subtropical and tropical
rainforest. Whether north-south climatic gradients were less strong than during the Late
Cretaceous is less clear because of the uncertain taxonomic affinity of some commonly
represented taxa, e.g. Casuarinaceae (Haloragacidites harrisii).
Palaeo-northern Australia
Lithostratigraphic evidence (Apthorpe 1988) indicates that Late Paleocene climates in the
Bonaparte and Browse Basins were very warm (upper mesotherm) as well as seasonally dry
(subhumid-humid). More generally, the shift from entirely coarse clastic to predominantly
carbonate sedimentation is seen as evidence that climates were relatively dry during the Early
Paleocene. The only palaeobotanical evidence for Paleocene climates in northeastern
Australia comes from a site on the Northern Tablelands of New South Wales. Here,
conditions were sufficiently wet (humid-perhumid) and warm (mesotherm range) to support
Austral Conifer Forest dominated by Araucariaceae and ferns. Nothofagus is absent despite
the moderately high elevation. Wildfires were common although the cause may have been
volcanism rather than a prolonged dry season. Indirect evidence for seasonally warm and wet
conditions across much of western Queensland is provided by deep weathering of Cretaceous
landsurfaces, although age control is poor.
Palaeo-central Australia
Reconstruction of Paleocene climates in central Australia is hindered by poorly constrained
ages and the unusual composition of the terrestrial vegetation. Nothofagus is rare or absent
and, assuming the source(s) of one dominant pollen type (Cunoniaceae) had similar climatic
preferences to the NLRs, then conditions were seasonally wet (humid) and relatively warm
(mesotherm range). The presence of Sparganiaceae swamps is consistent with sluggish flow
regimes and, by extrapolation, a pronounced dry season. Dinoflagellates imply that some of
the lakes or ponds were sub-saline although this could be due to an influx of saline
groundwater rather than a prolonged dry season. Silcrete began forming in the Eyre Basin.
90