Glacial Geology of the Reedy Glacier Area, Antarctica

Abstract

The Reedy Glacier is an outlet from the East Antarctic Ice Sheet and flows through the Transantarctic Mountains to the Ross Ice Shelf. The higher parts of the mountains consist of plateau remnants at about 3000 to 3500 m elevation. A shallow depression in this surface is filled with 40 m of till underlain by mass-wasted sandstone bedrock. The basal till consists of granite fragments, probably derived from a hill nearby. The remainder has a clay-rich matrix and contains fragments of igneous, metamorphic and sedimentary rocks that were probably derived from the plateau surface. All the till except the superficial layer was apparently deposited by temperate, wet-based ice. In an ice-free area at 1400 m elevation alongside the Reedy Glacier, about halfway between the East Antarctic Ice Sheet and the Ross Ice Shelf, stranded lateral moraines indicate former ice levels 750 m, 400 m, and 260 m above the present glacier surface. Granitic boulders on the surface at 750 m are highly weathered, those at 400 m are moderately weathered, and those at 260 m are virtually unweathered. Toward the head of the glacier these three sets of stranded moraines progressively approach each other and are also closer to the present ice surface. There is no evidence that the ice of the Polar Plateau has varied much since its establishment. Alongside the Reedy Glacier at about 1500 m elevation, 90 m of ice-marginal lake sediments are exposed. At present virtually no meltwater is present. Inactive solifluction flows occur further up the glacier at about 2000 m elevation. The till sequence on the high plateau is believed to indicate progressive refrigeration and the replacement of a small, local glacier by a temperate, local ice cap that later became polar and dry-based. The temperate ice cap must have antedated the Antarctic Ice Sheet and probably existed during the Pliocene. The variations in thickness of the Reedy Glacier after it had become an outlet of the East Antarctic Ice Sheet are thought to have been determined mainly by the position of the grounding line of the Ross Ice Shelf, which was controlled by eustatic changes in sea level, so that the glacier thickened during northern hemisphere glaciations. The lake sediments and solifluction flows indicate “interglacial” conditions 6° to 10° C warmer than at present.