OFR 151.pdf - CRC LEME

5. TIME SLICE K-5
Age Range: Early Campanian [83- ~70 Ma]
Zones: Nothofagidites senectus Zone
Upper Nelsoniella aceras to Xenikoon australis Zones
5.1 Macrofloras
Douglas (1994) has noted that leaf cuticle is often a major component in microfossil
preparations.
5.2 Microfloras
Marine and non-marine sediments, which preserve Early Campanian palynofloras, occur in
offshore basins along the southern, western and northern margins. The first appearance of
Nothofagidites is widely used as a marker for the basal Campanian and this may conceal
diachronous or time-transgressive trends in the first occurrence of other botanically important
species along the southern margin.
Like Lagarostrobos and Dacrydium, the first appearance of Nothofagus is of potentially
major palaeoclimatic significance, as three of the four living subgenera (Fuscospora,
Lophozonia, Nothofagus) are confined to relatively cool to cold (microtherm range) and
uniformly wet climates in Australia, New Zealand and southern South America. The fourth
subgenus (Brassospora), which is endemic to New Caledonia, New Guinea, is also confined
to uniformly wet climates but is tolerant of a wider temperature range (upper microthermlower
mesotherm).
The clade represented by Campanian Nothofagidites was ancestral to the four extant
subgenera (Dettmann et al. 1990) and its palaeo-distribution makes it probable that the genus
was adapted to extended periods of winter darkness (possibly deciduous) and high levels of
environmental disturbance. The latter characteristic is retained by many living Nothofagus
species whilst the deciduous trait occurs in several Nothofagus species that are confined to
upper subalpine and alpine habitats, e.g. N. gunnii in Tasmania.
Accordingly, the spectrum of responses to modern drought and temperature extremes makes it
unwise to rely too closely on modern bioclimatic data when interpreting Late Cretaceous
palaeoclimates. For example, the possibility exists that ancestral Nothofagus species were (or
included) shrubs occupying exposed and/or disturbed sites such as along rivers and therefore
that the relative abundance of its pollen may reflect edaphic factors rather than climate per se.
Conversely, there is weak evidence that some ancestral Nothofagus were growing in the
Eastern Highlands, implying some ecotypes were adapted to more stable environments. An
example is the high relative abundance of Nothofagidites senectus in the Wild Dog-1 well,
located on the southwestern margin of the Gippsland Basin adjacent to the South Gippsland
Range (Macphail 1993). Systematic analysis of Campanian microfloras across the Gippsland
Basin would help resolve this point.
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