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Victoria University Antarctic Research Expedition Science and Logistics Reports 1996-97: VUWAE 41

1 Aims

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1 Aims

The main goal of the project is to understand the Sirius Group tillite in the Dry Valleys area. The significance of this deposit centres on an intense international debate concerning the extent of the East Antarctic ice sheet three million years ago. The dynamic view in the debate favours a nearly complete deglaciation, while the stabilist view favours an ice sheet which formed nearly 14 million years ago and retained its shape through until the present day.

The aims of the field work, as established by the PGSF grant in December 1995, were to collect data for a geologic and geomorphic map of the Sirius Group at Table Mt and Mt Feather. Cores at least one metre long of the Sirius Group outcrops were to be obtained from at least three sites each at Table Mt and Mt Feather. Coring locations were to be selected on the basis of geomorphic mapping and previous sites where study samples were taken.

The achievements of the November - December 1996 field season were significantly greater than the initial goals of the project established in December 1995. Over the 23 field days, enough geologic and geomorphic data were collected to provide a detailed map of about four square kilometres on the northwest flank of Table Mt. Detailed glacial fabric analyses of the Sirius were made at 12 sites. Hand-held aerial photographs were taken of the area from an altitude of about 3000 metres. Included in the photographs were four GPS positions, accurately surveyed to within 0.5 metres with reference to the Table Mt trig.

A total of about 49 metres was drilled at seven locations on Table Mt. Of this, about 42 metres of core was collected, giving an average recovery rate of 87%. On average, the core holes were 3.5 metres deep, but two of those reached a depth of 9.5 and 8 metres. The significant amount of ice in the pores and fractures of the core was a surprise. The age and origin of this ice is open to much speculation and research.

Ground temperatures from the surface to a depth of 3.5 metres were measured in four holes. Measurements were taken at 25 cm spacings down the hole. These were taken for a duration of five days at one hole but for only one to two days at the other holes.

A full camp move to Mt Feather was not made due to the condition of the drilling equipment and high risk of minimal core recovery. Instead, we made a reconnaissance of Mt Feather with a light amount of drilling equipment. With a helicopter standing-by, two holes were drilled to a depth of 0.8 and 0.4 metres. This drilling established that the coring characteristics of the Sirius at Mt Feather were similar to those at Table Mt. We also established that the success of coring depends largely on the use of compressed air as a cooling and flushing medium for drilling these types of ice-cemented glacial deposits. Prior to leaving Table Mt, a reconnaissance was made for Sirius deposits at the same elevation as Table Mt and directly across the Ferrar Glacier on Knobhead. Outcrops of Sirius were not found, but the soil regolith on Knobhead was identical to that on Table Mt suggesting that Sirius may have also been deposited on Knobhead.