Cainozoic geology and geomorphology of the Wahgi Valley, central highlands of Papua New Guinea

The Wahgi Valley is a structural depression, between the Bismarck Fault Zone to the N and the Kubor Anticline to the S, which has been enlarged by erosional removal of N-dipping sedimentary rocks on the N flank of the Kubor Anticline. The geomorphic history of the area began when it became land about 35 Ma ago. The Wahgi Valley contains volcanic debris avalanche and lahar deposits in the W and fluviatile/lacustrine deposits elsewhere. The latter are dominated by undissected swamp and lake deposits in the We, and dissected fan and terrace deposits in the E. There is clear evidence of knickpoint retreat up the Wahgi River from the E, causing the fans to trench progressively from the E. Evidence from sediments, tephra, and landforms now suggests that reversal was probably restricted to the westernmost drainage, and any reversal of drainage occurred earlier than previously thought, perhaps 400 000 years ago.-from Authors