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

3 Scientific Endeavours and Achievements

3 Scientific Endeavours and Achievements

On 10 April 1997, a meeting was held at the School of Earth Sciences, Victoria University of Wellington, to present the preliminary findings of Antarctic field work carried out in the summer of 1996/97. The abstracts of three talks, presented at that meeting, provide a summary of scientific endeavours and achievements of the field work completed at Table Mt.

3.1 A Preliminary Report on Sirius Group Deposits, Table Mountain James Goff and Ian Jennings

Sirius Group deposits on Table Mountain appear to result from both advancing and retreating glaciers. The topography, however, is the result of glacial retreat and includes patterned ground, water-lain deposits, and mass movement features. Cores taken through the Sirius Group should help explain the role played by water in ice advance and retreat at the site, and in dating the event.

Fabric data from deposits at the southern end of Table Mountain indicate that this area was a confluence zone for ice emanating from the directions of the contemporary Tedrow and Ferrar Glaciers. However, the imprint of "Ferrar" ice dominates Sirius Group sediments at Table Mt. Other minor contributions of sediments were made from small mountain glaciers emanating from the saddle area between Table Mt and Navajo Butte. We believe that ice from these sources may have been sufficient to occupy the anomalous hollow (Figure 1) at Table Mountain which is devoid of glacial deposits.

Deposits that contain a small percentage of granitic clasts are found several hundred metres upslope from the prominent dolerite sill at Table Mt (Figure 1). The abundance of granitic clasts appears to increase down slope suggesting it was sheared up by glacial flow immediately downglacier of a confluence zone. Fabric measurements, taken from south to north along the length of Table Mt, indicate a reorientation of ice flow from west to southwest. Reorientation was caused by Table Mt obstructing ice flow which has resulted in the deposition of thrust-faulted lodgment tills and associated deposits. Lodgment and thrust-faulting may represent a period of glacial advance.

Ice retreat and down wasting has left an extensive ridge and hollow topography. Ridges generally consist of glacial diamictite, covered by a boulder lag, while the hollows consist of either conglomerate or sand. The deglacial environment appears to be dominated by water-lain deposits of which the conglomerate and sand suggest that both high and low energy regimes were involved.

Three distinct mass movement features cut across the ridge and hollow topography. Patterned ground, which is pervasive throughout the Table Mt area, is most prominent on these mass movement features but less prominent on the ridge and hollow topography. It is not clear if the degree of prominence expressed by the patterned ground, represents different degrees of activity, different ground materials, or different periods of generation.

3.2 On-Land Coring: New Developments Warren Dickinson, Pat Cooper, Bain Webster

Core drilling of permafrosted sediments is common and well understood in most Arctic environments, but in the cold, dry page break Antarctic environment it is at its infancy. Coring the Sirius deposits at Table Mountain was largely an on-site experiment because such permafrosted sediments do not exist in NZ or on Ross Island.

All drilling equipment had to be hand portable, and available in the field camp. Off the shelf HQ and NQ diameter core barrels and drill rods were used with a flushing medium of compressed air. The purpose-built, portable compressor could produce 50 cubic feet of air per minute at 30 psi which was pumped down the hole via an air swivel. The drill rods were rotated by a Sthil 056 motor mounted on frame with a torque bar which was pinned to the ground. Bit weight was controlled by the weight of the operator and any additional weight from the helpers. Pulling and lifting of the drill assembly was controlled by a hand winch via a single running block attached to a tripod.

Initial drilling showed that experimentation and modification of bit types was necessary to properly core the variety of lithologies contained in the Sirius. The flushing and cooling of the drill bit with compressed air was found to be critical. At all times the drill bit must be kept at sub zero temperatures to prevent melting of core and nearly instantaneous freeze in of the bit should rotation stop unexpectedly. Cooling of the bit depends on the temperature and volume of air entering the hole as well as the kerf and diameter of the bit. For a given air supply, a thin kerf and small diameter bit runs cooler than a thick kerf and large diameter bit. Diamond bits must be used to core hard and firmly cemented dolerite clasts, but tungsten bits must be used to core ice lenses and soft friable sands. Core recovery of conglomerates in ice-free horizons, which usually occur from the surface to 50 cm deep, was not possible. Loose clasts which are jarred from this horizon and fall into the hole must be either pulverized by further drilling or scooped out of the hole if core is to be recovered.

Considering the budget restraints and limited helicopter support the drilling project was extremely successful. With moderate adjustment and modification the existing equipment could be refined into a highly reliable and portable Antarctic drilling unit.

Final score at Table Mountain:
Total drilled: 49m
Total core recovered: 42m (86% recovery rate)
Total time in field: 24 days
Equipment loss: 1 diamond core bit and tungsten reamer
Cost of equipment and labour: $28,000 (this excludes rental and depreciation of equipment) or about $650 per metre of core

3.3 Ice and Temperature Signals from Sirius Group, Table Mountain Warren Dickinson

Core hole drilling of the Sirius Group at Table Mountain provided the opportunity to measure closely spaced (10-30cm) ground temperatures from the surface to four metres deep. These temperatures will provide background data for two areas of study. 1) Determination of the potential for periglacial or active ground movement that could produce patterned ground on Sirius Group sediments. 2) Calibration of oxygen isotope temperatures obtained from ice in fractures and in pores of the sediment. Although the Sirius was thought to have ice-filled pores below 50 cm, the amount and number of ice filled fractures found in the core was a surprise. Although this ice cannot be directly dated, stable isotopic measurements are critical to understanding its origin.

The equipment and methods used for measuring the temperatures were designed to be simple and economic. They also had to page break accommodate a range of unknown conditions. At the outset of the project, the depth and number of core holes was uncertain as well as the ability to actually measure the core hole temperatures.

The measuring system consisted of a digital thermometer calibrated for K-type thermocouples and 15 thermocouple wires from 0.5m to 4.5m in length. The core holes varied in diameter between 70 and 90mm and for this particular range a 50mm OD plastic pipe worked best for holding the wires down the hole. The relatively loose fit ensured that the plastic pipe would not get stuck in the hole. Thermocouple wires were brought down the centre of the pipe and out through holes at 0.25m intervals. The wires were taped to the outside of the pipe and bent to form whiskers protruding about 10mm outwards from the pipe. In this way, the wire whisker with the thermocouple junction on the end contacted the side of the core hole. Temperature measurements were taken over a period of five days at one hole but only for one day periods at four other holes.

Temperatures decreased with depth by 3.5_C per metre up to four metres depth (Figure 2). At four metres depth the average temperature, which varied by 2_C between the five holes, was −21.5_C. Temperatures measured 3-5cm below the surface in loose soil showed large variations. This was probably due to the degree of sunlight exposure at the surface. These variations appeared to affect temperatures down the hole to 0.5 m and possibly 1.0 metre deep. To confirm these temperature variations, measurements must be made over a period of weeks and probably through the winter.