BASAL ICE CONDITIONS OF THE ANTARCTIC ICE SHEET INTERPRETED FROM OLIGOCENE THROUGH PLEISTOCENE TILLS OF THE CAPE ROBERTS DRILLING PROJECT

Grain size analysis was done on diamictites of Cape Roberts drilling Project (CRP) for cores 1, 2 and 2A, with the purpose of reconstructing basal ice sheets conditions in East Antarctica in the Miocene through Pleistocene. Grain size distribution can give evidence of paleoenvironmental conditions and basal ice conditions to determine if diamictites are subglacial tills. Samples were selected from diamictites that are nonfossiliferous, structureless and fabrics typical of subglacial till. Preliminary results show higher concentrations of silt size particles in Late Oligocene to Early Miocene samples and sand size particles in samples of Pleistocene age. Higher silt content from older samples can be interpreted as greater amounts of basal meltwater in which subglacial grinding of larger particles creates silt size particles. In addition, younger samples with greater sand content can be interpreted as polar ice conditions like today in which the ice sheet may be frozen to the bedrock and there may be little, if any, meltwater. Furthermore, work will include geochemical analysis of sediment and particle size analysis of older samples of Oligocene age.