LANDSCAPE EVOLUTION OF THE CONVOY RANGE AND MACKAY GLACIER, TRANSANTARCTIC MOUNTAINS

We analyse the geomorphology and landscape evolution of the Transantarctic Mountains inland of McMurdo Sound and Cape Roberts. It is possible to distinguish a preglacial assemblage of landforms related to fluvial activity and a set of glacial landforms related to an expanded ice cover. The preglacial landscape is represented by a series of flattish erosion surfaces and escarpments that culminate in the Convoy Range at an altitude of over 2400 m. The surfaces are dissected by often sinuous valleys bounded by valley benches and/or rectilinear slopes. Landforms of glacial erosion comprise (a) glacial troughs, especially near the coast, (b) landforms of areal scouring on the flanks of Mackay Glacier and along the coast up to altitudes of 1450 m and (c) a remarkable suite of subglacial meltwater landforms including scablands, meltwater channels, plunge pools and potholes, the latter reflecting the sudden outburst(s) of a massive subglacial lake. Comparable meltwater landforms occur in the adjacent Dry Valleys block where they have been dated to the mid-Miocene. We conclude that, as in the Dry Valleys and the Royal Society Range, the landscape was eroded first by rivers with the aid of warm-based glaciers and secondly by an overriding ice sheet. The landscape had achieved essentially its present form by the mid-Miocene. Subsequent erosion is restricted mainly to the Mackay outlet glacier. The presence of drowned river valleys with rectilinear slopes extending below present sea level implies that there has been little, if any, tectonic uplift since the mid-Miocene. There is an impressive match with the initial findings derived from the Cape Roberts core immediately offshore.