Long-term landscape evolution in Australia



The main features of the Australian physical landscape are of the order of 107-108 years old. This contradicts the widely held view that little of the Earth's topography predates the Quaternary and that erosion cycles are carried to planation within tens of millions of years. Much of the Australian landscape must have developed over similar timescales to that of the tectonic evolution of the continent itself. The study of the geomorphology of such ancient terrains may therefore be seriously deficient unless it is considered within the context of continental-scale tectonic development. Application of this approach shows that there are strong links between the geomorphology of Australia and plate movements, ocean spreading, plate convergence, tectonostratigraphic terranes, orogenesis and epeirogenesis.

The most important factor contributing to the survival of ancient landscapes in Australia is the low rate of denudation which the continent has experienced during the Mesozoic and Cenozoic. This is largely a consequence of orogenic stability, although the absence of significant Quaternary glaciation may also be of importance. However, in order for landforms to have survived over such timespans, denudation must not only have been low, but must also have been highly localized over space and time. This has been the case both on a regional scale, with long-term denudation rates of 0-2 m Ma−1 in central Australia contrasting with higher rates along the continental margins, and on a local scale, with denudation confined to valleys, leaving divides and interfluves almost unscathed.