Stream Profile Change and Longterm Landscape Evolution: Early Miocene and Modern Rivers of the East Australian Highland Crest, Central New South Wales, Australia

Early Miocene basaltic lavas that flowed into river systems in central eastern New South Wales are still preserved as sinuous hill-top cappings. They permit reconstruction of many of the characteristics of the Early Miocene river systems and allow for comparison with the adjacent modern counterparts of these rivers. The long profiles of both the Early Miocene and modern valleys are rather similar and apparently exhibit adjustment to the lithologies of their channel substrates, as would be proposed under Hack's condition of dynamic equilibrium. Slightly less post-Early Miocene incision in the rivers' headwaters indicates, however, that the landscape has not experienced uniform catchment-wide downwasting, as would also be proposed by Hack. Traditional geomorphic models which propose declining relief and decreasing importance of lithological influences over long time periods also are inapplicable to the area. On balance, the most suitable model of the post-Early Miocene evolution of this area would incorporate slow rates of landscape evolution, the persistence, rather than waning, of lithological influences on river systems, and minor increases in relief. Such a model is probably applicable to other humid areas which are of moderate relief and have experienced tectonic stability.