THE GEOMORPHOLOGICAL SETTING OF THE SIRIUS GROUP OF THE CENTRAL/SOUTHERN TRANSANTARCTIC MOUNTAINS, ANTARCTICA

In the central/southern Transantarctic Mountains of Antarctica the Sirius Group visibly occurs across exceptional relief, from the highest mountains along the Beardmore Glacier above 4000 m asl to the current surface elevations of the upper Beardmore, Shackleton and Reedy glaciers. It has been shown 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. Hence, the current topography would not allow the deposition of basal tills on topographic highpoints, rather the implication is that these are relict deposits, left perched as adjacent outlet glaciers deepened their beds and steadily increased local relief. Wide expanses of ice-free ground covered by Sirius Group deposits occur at lower elevations in the upper Shackleton Glacier region on Bennett Platform and the Roberts Massif. Here, the surface morphology of the Sirius Group also reveals them to be distinctly relict deposits, which have experienced subsequent down-cutting of adjacent outlet glaciers and tectonic modification. Consequently, there should be an exceptional age-range in the deposits occurring in this region across thousands of metres of relief and, by analogy to the better-dated surface topography of the northern Transantarctic Mountains, would possibly contain glacial sediments of the Eocene.