OFR 151.pdf - CRC LEME

5. Facies architecture and lithostratigraphy
Many sediments and sedimentary sequences are the result of cyclic processes operating under
particular environments (Schwarzacher 2000). The environmental signatures of these
processes may be physical, geochemical or architectural.
An example of a sediment type that has well-defined climatic implications is aeolian dust
preserved in the Late Cenozoic regolith in arid and semi-arid south-west Western Australia
(Glassford and Semeniuk 1995). Cool water shelf carbonates provide evidence for SSTs
along the southern margin during the Oligo-Miocene (references in Nelson and James, 2000).
Elsewhere, Alley et al. (1999) have used sediments infilling palaeodrainage systems to
reconstruct a weathering history for central southern Australia; Dingle and Lavalle (1998)
have used chemical weathering and maturity of sediments to infer palaeoclimates in western
Antarctica during the Late Cretaceous and Cenozoic; and Pederson et al. (2000) have shown
that sediment production and delivery to piedmont fans can be correlated with climatic
change during the Mio-Pliocene in tectonically quiescent areas.
Sequence stratigraphy concepts have revolutionised the interpretation of sedimentary
sequences infilling continental margin basins (cf. Haq et al. 1987, Miall 1995, Bohacs and
Suter, 1997). Gammon et al. (2000) and Li et al. (2000) provide examples of the role of
oscillating sea levels in determining sedimentation patterns (and therefore stratal architecture)
in the Eucla and Otway Basins, respectively. However, sequence stratigraphy concepts are
difficult to apply inland where deposition may not be directly linked to changes in relative sea
level (McCarthy and Plint 1998, McCarthy et al. 1998).
6. GCM Modelling
General Circulation Models (GCMs), which simulate past climates, increasingly are being
used as an alternative to reconstructions founded on proxy-climatic data. For example, GCMs
have been used to model conditions during Quaternary glacial and interglacial cycles and to
predict how sensitive regional climates will be to future changes in atmospheric CO2. Similar
models have been used to reconstruct mid Cretaceous and Early Eocene climates for the
Australian region (Frakes 1997, 1999), or the globe as a whole (cf. Sloan 1994, Barron et al.
1995, Sloan and Rea 1995, Price et al. 1998, Haywood et al. (2000).
Climatic predictions, however, may be difficult to test, e.g. because of uncertainties in the
boundary conditions such as the extent of the East Antarctic Ice Sheet during the middle
Pliocene. At present, the resolution provided by GCM simulations is too coarse to accurately
predict past environments at the regional geographic scale. A recent example is a model that
failed to ‘predict’ the formation of bauxite deposits in Tertiary Australia (Price et al. 1997,
Price 1998, Taylor 1998). Thus palaeobotanical and related evidence are likely to remain an
essential part of the data used to define and test boundary conditions used in modelling
experiments (Thompson and Fleming 1996, O’Brien 1998).
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