LATE QUATERNARY GLACIAL HISTORY OF THE SOUTH ORKNEY PLATEAU, ANTARCTICA

Piston cores from the South Orkney Plateau penetrated overcompacted diamictons in water depths of up to 250 m. Detailed textural and petrological analyses of these diamictons indicate that they are basal tills. Seismic records from the plateau show a widespread surface of glacial erosion and provide additional evidence of an ice cap grounded to a depth of 250 m. Piston cores from the slope of the plateau penetrated diatomaceous muds resting directly on poorly sorted muds with very little to no biogenic material. The ice-rafted debris in these glacial-marine sediments is composed almost exclusively of material derived from the South Orkney Islands. This implies deposition beneath an ice shelf as opposed to iceberg rafting. In contrast, diatomaceous muds contain relatively abundant exotic iceberg-rafted material and reflect a glacial-maritime setting similar to that of today. The sharp contact separating diatomaceous surface sediments from basal tills and sub-ice shelf deposits indicates that the ice cap and ice shelf retreated from the plateau rapidly. Radiocarbon dates for diatomaceous muds from a glacial trough on the plateau indicate that the ice cap and ice shelf retreated from the plateau prior to 6000 to 7000 years ago. The homogeneity of surficial diatomaceous sediments suggests that sea ice conditions over the plateau have not changed radically since that time. © 1990.