The Geomorphology of the Miller Range, Transantarctic Mountains with notes on the glacial history and neotectonics of East Antarctica

Abstract

Abstract The geomorphology and glacial history of the Miller Range on the edge of the Polar Plateau in the central Transantarctic Mountains is described. Three high-level glacial erosion surfaces are mapped and these surfaces represent progressive degradation of an original peneplain by successive advances of the continental ice sheet. Extrapolated to the coast they correlate with a summit erosion surface 1,600–1,900 m above the Ross Ice Shelf. During this early Pleistocene period of glaciation, the level of the Polar Plateau was apparently 800–1,000 m higher than at present. Following a major interglacial hiatus, the present glacial valleys were cut, deepened, and filled by ice, which gradually receded leaving a sequence of recessioml moraines. During this younger Pleistocene glaciation the Polar Plateau was no more than 300–400 m above its present level. Regional correlations with the McMurdo Sound district are suggested. The older glacial surfaces are correlated with the Insel Glaciation, the younger moraines with the Victoria Glaciation, and the interglacial hiatus with the Scallop Hill Formation containing Chlamys (Z.) anderssoni of probable mid-Pleistocene age. The present cycle is one of slow glacial retreat and correlates with postglacial retreat of the Antarctic ice sheet and isostatic rebound of the coast. Raised beaches, with the Adamussium colbecki fauna, along the Victoria Land coast indicate a 20–40 m rebound since the Climatic Optimum. The apparent level of the Polar Plateau appears to be controlled by: (a) Quaternary elevation of the Transantarctic Mountains; (b) Glacial downcutting by the outlet glaciers; (c) Eustatic rise and fall in sea level. Rises in plateau level and advances of outlet glaciers correlate with grounding of the Ross Ice Shelf and hence with glacial periods of falling sea level. This indicates an in-phase relation of expansion of the Antarctic ice sheet with glacial advances elsewhere on earth, and leads to rejection of theories of glaciation which demand an out-of-phase relation. The neotectonic history of East Antarctica is briefly reviewed. Deformation of the early glacial surfaces and geophysical evidence support crustal thickening and regional elevation—perhaps as rapid as 1 ft/1,000 years—along the Transantarctic mountain chain. Complementary subsiding regions with a thinner crust are the Polar Basin and the Byrd Basin. Elevation of marginal fault-block mountains and subsidence of interior basins dominate the neotectonic and glacial history.