Cenozoic landscape evolution of the Convoy Range to Mackay Glacier area, Transantarctic Mountains: Onshore to offshore synthesis

On the basis of geomorphic mapping, we reconstruct the landscape evolution of the Convoy Range to Mackay Glacier area of the rifted margin of the Transantarctic Mountains and compare the land record with that obtained from offshore marine sedimentary rocks in the Ross Sea. Three landform assemblages reflect (1) fluvial planation and dissection, (2) local glaciation under temperate conditions, and (3) overriding by the East Antarctic Ice Sheet. Overall landscape evolution is typical of a passive continental margin. Contrasts in morphology between the Convoy Range and the adjacent Dry Valleys and Royal Society mountains reflect the varying location of the initial drainage divide in relationship to the rifted coast. In a wider synthesis we draw the following conclusions for the 260-km-long McMurdo sector of the Transantarctic Mountains. Denudation since rifting at ca. 55 Ma has removed a wedge 4-7 km thick at the coast, declining inland to similar to1 km. Most denudation occurred in the Eocene from planation and incision of river valleys near the coast. A subsequent pulse of denudation, most rapid at 34-31 Ma, and declining until ca. 17 Ma, coincided with further crustal extension and a change from cool temperate to polar climate. During the same interval, there was a progressive decrease in landscape modification by warm-based glaciers and/or rivers. Between 14.8 and 13.6 Ma the maximum overriding Antarctic ice sheet flowed northeastward across the mountains, leaving meltwater features crossing high-altitude saddles and areally scoured bedrock near the coast. Since 13.6 Ma, the landscape has seen little change under a hyperarid polar climate, either by local glaciers or subaerially. Fragile middle Miocene surficial deposits still survive. There has been tectonic stability since the middle Miocene.