Geological and geomorphic data and Sirius Group core analysis (stratigraphy, petrographical analysis, ground temperature and isotope analysis) from Table Mountain to determine the depositional history

The depositional and post depositional history of the Sirius Group tillite in the Dry Valleys area was investigated to resolve the ongoing debate as to whether the East Antarctic ice sheet formed 14 million years ago and retained its shape until present day (stabilists view) or if the nearly complete deglaciation of the East Antarctic Ice Sheet occurred 3 million years ago explaining the presence of rare marine diatoms in the Sirius Group (dynamic view). Detailed geological and geomorphic data was collected at 12 sites of the Sirius Group at Table Mountain and Mt Feather. Hand-held aerial photographs were taken of the area from an altitude of about 3000m. Enough data was collected to provide a detailed map of about 4 kilometres square on the northwest flank of Table Mountain. Cores were drilled in the Sirius at Table Mountain to gain information on its depositional history that cannot be determined from surface exposures. Coring locations were selected on the basis of geomorphic mapping and previous sites where study samples were taken. A total of 49m was drilled with 42 m of core recovered (87% recovery rate). On average, the core holes were 3.5m deep but two of them reached depths of 9.5m and 8m. Each core was analysed (stratigraphy and petrographical analysis) comparatively to determine the cause and relative timing of mineral dissolution and precipitation (mineral diagenesis). Stable isotope ratios of ice in pores and fractures was measured to provide important clues about the post depositional history of the Sirius. In addition to core drilling, closely spaced (10-30cm) ground temperatures from the surface to 4m depth were recorded from 4 holes to provide background information to (a) determine the potential for periglacial or active ground movement that could produce patterned ground on Sirius Group sediment and (b) calibrate oxygen isotope temperatures obtained from ice in fractures and in pores of the sediment. Temperature measurements were taken for a duration of five days at one hole but for only one to two days at the other holes. A reconnaissance of Mt Feather was completed and two holes were drilled to a depth of 0.8 and 0.4m.