The age of Canberra landforms

Abstract

The interpretation of Canberra's landforms as unexhumed survivals from Bowning faulting and mid‐Devonian vulcanicity is opposed. Some major faults are truncated whereas sharp scarps coincide with others. In the nearby Taemas area, the Canberra‐Yass Plains cut across Tabberabberan folds. Summit surface remnants surviving high in the A.C.T. Ranges and discordant river gorges are incompatible with extreme age of the relief. River nick‐points and steps between surfaces are some related and some unrelated to faults, with like import. Stripping of the Murrumbidgee Batholith, also of Bowning age, would have caused substantial filling of the Canberra Rift; during subsequent removal, erosion would not have entirely respected Silurian rocks similar in resistance to Devonian fill. Permian rocks to the east must in part derive from erosion of the Canberra area. Local rates of denudation of 5 cm/1000 y. are hard to reconcile with survival of high steep relief from the mid‐Devonian. Alternative explanations are given for those characters of the Fyshwick Gravels which led them to be regarded as Permian glaciofluvials. The same evidence supports Browne's standpoint that the relief is polycyclic through epeirogenic uplift at intervals, together with posthumous movement along some old faults.