OFR 151.pdf - CRC LEME

INTRODUCTION
Mineral resources, whether precious or base metals, hydrocarbons or groundwater, continue
to underpin the Australian economy.
In most cases, the geologic environment controls mineral formation. Minerals found in
alluvium (placer deposits) or weathered bedrock (saprolite deposits), and groundwater and
hydrocarbon reserves are exceptions in that these have indirect or direct links to past climates
and/or vegetation.
This report reviews palaeobotanical and related data for climatic change in continental
Australia during the Cretaceous (141-65 Ma) and Tertiary (65-1.78 Ma).
Amongst the more unmistakable indicators of climatic change are the fruits and foliage of
trees whose nearest living relatives (NLRs) are confined to tropical rainforest, and the skeletal
remains of freshwater crocodiles, dolphins and turtles preserved in the (now) arid north of
South Australia. The fossil cysts of algae and the spores and pollen of the higher plants
provide less obvious but much more widespread evidence of past climates. The same
microfossils also provide a cheap, relatively precise means of dating the host sediments.
The relationships between plants, climate and other elements making up ancient or 'hidden'
(Fortey 1993) landscapes remain speculative. However, it is certain that environmental forces
in the past included extreme (catastrophic) terrestrial and extraterrestrial events as well as
more gradual changes in rainfall and temperature (Budyko 1999). The relative importance of
the individual processes can be difficult to unravel. Nonetheless, there is every reason to
suppose that ecological relationships were varied during the Cretaceous and Tertiary as they
are now, and many organisms were able to reproduce and disperse under less than optimal
conditions.
For these reasons, this monograph briefly discusses the strengths and weaknesses of
palaeobotanical and other forms of proxy-climatic evidence, as well as modern bioclimatic
relationships. These relationships provide benchmarks for inferring regional trends in
temperature and rainfall during the Cretaceous and Tertiary.
Sloan and Morill (1998) claim that terrestrial palaeotemperature is the key to understanding
the past. In Australia, rainfall is equally or more important and trends in the amount and
seasonal distribution of rainfall in the past is a primary focus of the review.
A. RELATIONSHIP OF THIS STUDY TO PREVIOUS REVIEWS
a. Previous reviews
Numerous papers and monographs purporting to review the evolution of the Australian
environment during the Mesozoic and/or Cenozoic are in print. In spite of ambitious titles
that imply an Australia-wide coverage, reconstructions published before about 1990 are
almost always based on specific deposits (usually in southeastern Australia) that represent
relatively short intervals of geologic time.
This situation changed dramatically in 1994 with the publication of History of the Australian
Vegetation: Cretaceous To Recent (Hill 1994a) for two reasons. Firstly, the majority of
articles did attempt to review all published data on a continent-wide basis, e.g. Quilty (1994)
and Taylor (1994). Secondly, for the first time a concerted attempt was made to incorporate
unpublished data generated by the earth resources industries, e.g. Dettmann (1994) and
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