OFR 151.pdf - CRC LEME

Due to complex tectonic processes, the ‘age of exposure’ (Taylor 1994) only provides a rough
guide to the depth of the weathering profile across Australia (Figure 1). For example,
Tertiary igneous and volcanoclastic rocks on the Southeastern Highlands of New South Wales
have developed a deep regolith (and fertile soils) whilst Precambrian quartzites and
Palaeozoic limestones in Tasmania are characterized by thin regoliths (and highly infertile
soils).
1.2.2 Role of plants
Plants contribute to the weathering processes (and CO2 levels in the atmosphere) by the
physical action of roots or via organic acids and methane released by living and decaying
plant matter.
Aluminium or iron-rich crusts (bauxite, ferricrete, laterite) reflect the preferential leaching of
silica under tropical (usually rainforest-supporting) climates. The same phenomenon can
occur in much colder climates. For example in basaltic areas of Iceland, the weathering
release of Ca 2+ and Mg + to streams is two to five times higher in vegetated areas than in
barren areas (Moulton and Berner 1998). Conversely, Meunier et al. (1999) have noted that a
significant part of the silica (SiO2) dissolved from the parent rock is retained in soils as
(biogenic) phytoliths.
Figure 1: Age of exposure of landsurfaces (from Taylor 1994)
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