Age of Sirius Group on Mount Feather, McMurdo Dry Valleys, Antarctica, based on glaciological inferences from the overridden mountain range of Scandinavia

A striking difference in the geomorphology of the ice-sheet overridden lowlands and ranges in Scandinavia and the Wilkes Basin–Transantarctic Mountains region in Antarctica is the occurrence of basal till sequences (of the Sirius Group) on summits and interfluves in the Transantarctic Mountains and the lack of basal tills on corresponding surfaces in Scandinavia. From the pattern of glacially eroded surfaces and preserved preglacial surfaces in northern Sweden, we infer altitudinal and lateral patterns of glacial erosion and deposition governed by topography-dependent basal thermal regimes. Furthermore, summits and interfluves in northern Sweden are often remnants of preglacial surfaces. Consequently, these preglacial surface remnants were preserved underneath patches of cold-based ice. We conclude that the subglacial thermal zonation of ice sheets overriding peripheral mountain ranges is self-sustained by topography; i.e., cold-based ice relates to topographic highs and warm-based ice to topographic lows. We use these inferences to explore the glaciological implications for the Sirius Group sequence on Mount Feather, McMurdo Dry Valleys. A glaciologically plausible explanation for this deposit and similar Sirius Group sequences on dissected summit and interfluve surfaces in the Transantarctic Mountains is that deposition occurred before the bulk of the relief formed. The present relief in the Mount Feather vicinity is at least 11 Ma old. Consequently, the Sirius Group at Mount Feather is at least of middle Miocene age.