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 lowl ands and ranges in Scandinavia and the Wilkes Basin-Transantarctic Mountain s region in Antarctica is the occurrence of basal till sequences (of the Si rius 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 n orthern Sweden, we infer altitudinal and lateral patterns of glacial erosio n and deposition governed by topography-dependent basal thermal regimes. Fu rthermore, 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 subgla cial thermal zonation of ice sheers overriding peripheral mountain ranges i s 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 S irius Group sequence on Mount Feather, McMurdo Dry Valleys. A glaciological ly plausible explanation for this deposit and similar Sirius Group sequence s on dissected summit and interfluve surfaces in the Transantarctic Mountai ns is that deposition occurred before the bulk of the relief formed. The pr esent relief in the Mount Feather vicinity is at least 11 Ma old. Consequen tly, the Sirius Group at Mount Feather is at least of middle Miocene age. ( C) 1999 Elsevier Science B.V. All rights reserved.