OFR 151.pdf - CRC LEME

SECTION 8 (CONCLUSIONS)
Climatic inferences for each of the eleven Cretaceous and Tertiary time slices and seven
geographic regions are summarised in Tables 8a and 8b, respectively. These inferences
represent highly simplified versions of the data presented in Appendices 1-3 and summarised
in Sections 3-8 and must be treated as working hypotheses for reasons given in the
Introduction and re-iterated below:
• Each of the seven geographic regions almost certainly encompassed a wide range of
bioclimates at any particular period within the Cretaceous and Tertiary.
• Each of the eleven time slices almost certainly encompassed a number of shorter-term
climatic excursions imposed upon the longer term climatic trends.
• Many of the sedimentary sequences and spot samples represent very short intervals of
geological time.
• The fossil floras are strongly biased towards species living in mesic (environmentally
complacent) habitats, in particular plants living on coastal plains (fluvio-deltaic
environments) and along the shorelines of lakes or riverbanks. Plants living in
interfluve habitats are less likely to be represented in the fossil record. The relative
representation of plants that produce and widely disperse miospores in very large
numbers is exaggerated in large/deepwater lakes and analogous marine environments
(Neves Effect).
• The distribution of living plants (NLRs) provides only a general guide to the ecology
of fossil taxa, due to the climatically forced extinction of many genera, species and
ecotypes (most gymnosperms, ferns and fern allies) or adaptive radiation into novel
environments (many woody angiosperms and herbs). It is emphasised that none of
the NLRs of plants forming the Cretaceous to Paleocene vegetation in high to polar
latitudes are adapted to prolonged winter darkness under mild (upper microthermlower
mesotherm) conditions. Accordingly it is reasonable to assume that the
ecophysiological adaptations of these taxa to thermal and water stresses were
different from the presumed living relatives.
• Shorter-term trends in community composition and structure almost certainly reflect
forcing factors other than rainfall and temperature. The more important of these are
low light intensities during the Cretaceous and strongly leached, infertile soils during
the Tertiary. The role of volcanism and wildfires is less clear although both were part
of the Cretaceous and Tertiary environments.
Irrespective of the mostly low taxonomic and ecological resolution, the palaeobotanical (and
related) evidence is adequate to infer qualitative long-term trends in the Early Cretaceous,
Late Cretaceous and/or Tertiary climate for many regions of Australia with moderate
confidence.
8.1 Results in retrospect
8.1.1 Palaeoclimatic records
• Long-term trends correspond well with changes in global climate documented
elsewhere. Anomalies such as the persistence of very warm to hot conditions at high
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