Determination of the Sirius Group (Neogene deposits) mode of deposition at Allan Hills, Mt Feather and Table Mountain

An ancient glacial deposit termed the Sirius Group is a collection of Neogene deposits that crop out at high elevations throughout the Transantarctic Mountains (TAM). The paleoflow direction and how the Sirius Group was deposited, whether by valley glacier or continental ice sheet, by wet or dry based glacial ice or by a single depositional event or several overriding events was determined at Allan Hills. This low nunatuk has a mean elevation of around 2000 m above sea level, occupying a low point in the TAM, making the site susceptible to overriding by the East Antarctic Ice Sheet during minor volume fluctuations. The area was geologically mapped in detail. The deposits were studied to interpret the nature of the ice that deposited it by detailed investigations of selected major outcrops including orientation measurements of clasts and deformational features at both measured outcrops and stop locations and deposits were described in terms of texture, clast shape, fabric and composition. Rock and surface samples of several deposits of glacial debris and related features were collected for analysis. The orientation on abraded (striated) and faceted clasts throughout the study area was recorded. Striation direction was measured on lodged boulders in deposits and samples for matrix texture and palynology were taken. Several deposits were surveyed for further striation direction and measuring spot heights of the surface on which the Sirius was deposited, providing data for reconstructing the landscape during the deposition of the Sirius deposit. Surface samples and glacial deposits taken at key locations in Allan Hills and features judges to be much younger were collected for surface age dating of cosmogenic isotope. Glacial deposits near the edge of the Manhaul Glacier were studied in detail with glacial abrasions on bedrock and stone surfaces documented and their orientations measured. Mapping of the southern extent (or distribution) of the deposits in the central Allan Hills was completed using differentially corrected GPS to establish stratigraphic relationships to the Sirius Group. Samples from boulders in the Sirius deposits and more distant deposits were collected for surface age dating of cosmogenic isotopes. Samples were also taken of features judged to be much younger, and from surfaces close to the present ice where fresh glacial striae indicate very recent exposure. A minimum age for the formation and rates of erosion for the area was determined. The study was expanded to Table Mountain (an area similar in elevation to Allan Hills but the deposits are more varied) and Mount Feather (highest elevation deposits of the Sirius Group in the Dry Valleys) to provide a regional perspective. Outcrops were described (stone orientations, linear glacial abrasions, planar deformation structures) and samples were collected for thin sectioning, laboratory analysis, clast orientations, linear glacial abrasions and planar deformational structures.