Post-palaeozoic uplift history of southeastern Australia revisited: Results from a process-based model of landscape evolution

Developments over the last decade in the debate concerning the geomorphic evolution of the southeastern Australian highlands are reviewed, taking as a starting point the model of passive denudation and isostatic rebound of a Palaeozoic mountain belt presented by Lambeck and Stephenson (1986). This model has been popular in the geomorphological community because it provides a quantitative framework to explain the very low rates of landscape evolution inferred from most geomorphological studies. The model has, however, also been criticised for its treatment of erosion as being linearly dependent on elevation, as well as for its predictions of regional uplift and denudation patterns that are not in accord with inferences from fission-track thermochronological data. First results of a new physical process-based model for large-scale, long-term landscape evolution in the southeastern highlands are presented. These show that the denudation history and drainage development of southeastern Australia can be explained to a first order without invoking large-scale mid-Cretaceous or Tertiary uplift events. The model predicts drainage patterns in southeastern Australia to have evolved by rearrangement of an initially northwesterly directed drainage net, caused by drops in base-level during Mesozoic rifting along the southern and eastern margins of the study region. The geomorphology and available fission-track data in the Snowy Mountains region (and possibly also in the Bathurst - Blue Mountains region) do require renewed (mid-Cretaceous?) uplift to have taken place. The model results are discussed in the light of recent controversies surrounding the southeastern highlands-their uplift history, denudation rates, depth of denudation of the coastal strip and inferred Mesozoic drainage patterns.