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The aim of this event was to look at raised beaches along the Scott Coast from Cape Bernacchi to Dunlop Island. These features have developed since the last glacial maximum approx 18,000 years ago when the ice sheets were at their greatest extent. The weight of the overlying ice depressed the land which has been slowly rebounding after melting of the ice. While rebounding a series of beach ridges were formed.
One part of the project is to date the beach ridges and associated rock platforms by three different methods and obtaining their relative heights above sea level today. This will allow modelling of the volume and extent of the ice during the last glacial maximum.
To obtain a height above sea level today it is necessary to know where sea level was on the raised beach ridges. The second part of the project looks at the modern beach formation. Linking processes found here to features in the raised beaches should give an accurate position of sea level on the raised beaches.
The third part of the event was to use glacial striations, moraines and cosmogenic dating to work out whether the ice depressing this part of the coast came from an expansion of the Wilson Piedmont Glacier or an advancement of the Ross Ice Shelf onto the coastline.
Pre-season training course: This could do with some revision. The weekend course in Christchurch involved a lot of lectures which did not seem to be particularly relevant. In terms of the science side of things, the brief five minute talks given to everyone is possibly all that is required to advise other science parties. At this point, if there are other groups doing science of interest this can be followed up in person.
The practical sessions were ok, but it may be preferable to ask people to do a first aid course instead of trying to teach everything in such a short length of time (Christchurch component).
An alternative bad weather option needs to be considered for the Flock Hill training. The science parties had no proper training in setting tents up in a field situation due to the bad weather which makes things more difficult in Antarctica.
Two boxes of equipment were shipped to Antarctica before the event. These were non-delicate equipment and very tough cardboard boxes were suitable. They arrived in Antarctica in good condition. We required excess hand carry for equipment such as computers. Getting the excess weight allowance was not a problem and went smoothly. It is suggested that it is made clear this is likely to be taken off the person so should be packed accordingly (ie. packaging around the computer).
Despite a delay in arriving at Scott Base everything at went smoothly in the time before we went into the field. We were warmly welcomed to Scott Base and the staff were most helpful with the endless questions. Our equipment had arrived and was in order. The field training seemed to take up a great deal of the time we had due to the overnight exercise being delayed (New Years Eve). Excusing Julie Quinn from the overnight exercise allowed the science preparation to be done without a last minute panic. The equipment the party received was in good condition and it was easy to change
Parts of the field training were not particularly useful to our event (much of the snowcraft was not required as we were never on any permanent snow). However, there were other groups on our AFT who needed this training. We had a brief rundown (10 minutes) on the sea ice which was the most important part of our training. Perhaps next summer if there was a second AFT training person the crevasse part of the course could be dropped and this time spent on sea ice training. A fuller brief to the AFT people beforehand may allow this to be organised.
Our event was supported by both American and New Zealand helicopters. We had 5 double shuttles in total, 2 by K03 and 3 by the Americans as well as other contact, such as resupply and taking rocks out of the field. We were most impressed by both crews, finding them friendly and professional in their approach. Baring one move the helicopters shut down initially to organise gear which was useful as it gave us a chance to describe where we wanted to be placed and other such details. The crews were helpful in choosing a suitable site on the ground, giving us plenty of time (considering we were only seeing it for the first time) and consequently we had excellent camp sites. When working with the American helicopters we had sling loads. No training had been given to us in New Zealand about to how to load a sling load etc. This was not a problem once the pilot had explained what he wanted but it would be a useful part of the pre-season training. A little more communication from Scott Base as to when the helicopter is arriving, should the schedule be changed, would be useful instead of us needing to contact Scott Base. This caught us out on one occasion when the weather was bad at Scott Base and we were not aware (packed up camp), only to be told later after 'calling Scott Base. Overall we were very happy with our helicopter operations.
Attached are four maps detailing camps and sites where holes were dug and rock samples taken. Also attached is a copy of a section from the USGS topographic map which has inaccuracies close to Kolich Point and between Kolich Point and Spike Cape.
We had no meteorological equipment to provide a detailed account of the weather encountered. In general the range of temperatures experienced were quite warm. On a few occasions the temperature may have reached +5° C but on most days was between −5° and 0° C. Wind chill was usually the only thing that made the temperature feel cold. We had a variety of cloud cover, with considerable variation during the day from 0/8 to 8/8. In general the coast seems to be in a fringe zone between the weather that the dry valleys and mountains receive and the weather of the Ross Sea/Ross Island area. Often this fringe zone meant the weather would look bad elsewhere while still being good over the coast. We had three spells when there was snow. These were short lived (1/2 to 1 day) and were not bad enough to hinder work to any great extent. The second snowfall put an estimated 10 - 15 cm of fresh snow (undrifted) on the ground while the others were considerably less. The weather was of little hindrance except where the snowfall covered rocks!
There were no accidents during the field season.
Ration Boxes: Overall these are great! A few items that could be added to the boxes without great changes are some more sachets or similar to make the main meal interesting (such as "cook-in-the-pot" sachets). For milo drinkers it was disappointing to see that this is not standard in the boxes as well as tea and coffee. The additional items selected to take into the field are important in keeping variety in the food (and hence interest). We found the small bags of scroggin were not as popular as muesli bars and chocolate as they tended to burst and fill pockets/packs with peanuts etc.
The only risk with the Scott Base diet is getting fat! The few days at Scott Base were great with lots of variety and choice, all done to a high standard.
See attached pages.
While at Scott Base the historic hut at Hut Point (Scott's 1902) was visited (1 January 1997). General observations were that it has been kept in good order, both inside and out.
This event was the first year of a two year plan of field work in the area. It was difficult for the second year to be planned well without the knowledge obtained from the first seasons field work. For a project like this I think that it is important that both seasons work is evaluated in peer review as a single event. This does not put the second seasons field work in jeopardy when the whole project requires both.
Antarctica New Zealand is in the ideal position to cater for this event, the location of Scott Base allows easy access to the ice free coast where post-glacial rebound is occurring. With the combined logistics of the Americans the potential support is far greater than anyone else could offer. The project is a joint effort between Victoria University of Wellington and The Australian National University. This is a valuable collaboration as it allows the experience and knowledge of scientists working on the same ice sheet reconstruction problem in East Antarctica to be applied to the Scott Coast to provide a more holistic approach to the problem.
The aim of this event was to look at raised beaches along the Scott Coast from Cape Bernacchi to Dunlop Island. These features have developed since the last glacial maximum approximately 18,000 years ago when the ice sheets were at their greatest extent. The weight of the overlying ice depressed the land which has slowly rebounded after the ice melted. While rebounding a series of beach ridges were formed.
One part of the project is to date the beach ridges and associated rock platforms by three different methods and obtaining relative heights above sea level today. This will allow modelling of the volume and extent of the ice during the last glacial maximum. There has been approximately 120 m of sea level rise since the last glacial maximum, with the well constrained northern hemisphere ice sheets contributing about 90 m. The Antarctic contribution is less well constrained, so by this study combined with other similar studies from East Antarctica a better idea of the amount of ice in Antarctica during the last glaciation should be obtained.
To obtain a height above sea level today it is necessary to know where sea level was on the raised beach ridges. The second part of the project looks at the modern beach formation. Very little work has been done on Antarctic beaches and the processes which form them. Studying the modern beaches along the Scott Coast will add enormously to this knowledge. By linking processes found on the modern beaches to features in the raised beaches should give an accurate position of sea level on the raised beaches.
The third part of the event aims to identify the provenance of glacial moraines along the Scott Coast and to provide a chronology for retreat of ice from this area using surface exposure dating techniques.
The work was carried out from a series of four camps along the Scott Coast, one at Marble Point which covered the area from South Stream to Gneiss Point, one at Kolich Point, one at Spike Cape which covered both tombolos and the mainland and finally one at Dunlop Island.
There are well developed boulder beaches along most of the coast which are dominantly storm deposits with very little ice influence. A good correlation was able to be established between the size of ridges and materials to the energy of formation. Links were established between active processes and sediments found in the raised beaches, such as the evidence of a shallow tidal channel features on Marble Point. Well developed raised rock platforms between the beaches should provide the key dating tool (surface exposure dating). These will allow a better record of relative sea level fall in the area than has previously been available. Links have been established between the various dating techniques. Surveying of marine limits and beach profiles
The principal objectives for the field season were:
Four benchmarks were put in for the event by the surveyors (K191) which were linked to sea level via the tide gauge at Cape Roberts. These were a combination of existing marks and two new ones at Dunlop Island (iron rod on top, by the large cairn), Spike Cape (on a large boulder near the isthmus connecting the mainland to the two tombolos), Kolich Point (on the 4th raised ridge at the point) and at Marble Point (WALO). This gave us a good starting point to run a GPS base station from, as well as a point to tie the levelling to for good height control. The GPS run was a Trimble Pro-xl and was used to give approximate locations for each surface exposure sample site, sites of each hole dug and other significant point.
Levelling was done using a dumpy level to reduce problems with battery power and reliability in cold weather which may have occurred using an EDM (electronic distance meter). This did mean a lot more time was spent on surveying than may have otherwise been needed but gave us height locations within 10 cm. A line was run out from the survey marks along the beaches to
When these data are fully reduced there will be profiles of the beach ridges extending laterally over varying energy conditions along the coast. This should give an idea of the relationship between energy and height, as well as starting to give an idea of any differential uplift occurring on the coast. Where the marine limit was previously poorly constrained these surveys should give the height with more accuracy.
Some of the beaches in this area have been dated previously using radiocarbon from shells, bones, and other organic remains. There are difficulties in the Antarctic with calibration of these dates due to the long mixing time of Antarctic Ocean water. But they still remain a viable dating tool. This was one method used. Where shells were found to be in situ these have been taken. Two species were found to be dated, Laternula elliptica and Adamussium colbecki . These were only found in the lower energy, sandier beaches.
Lower energy beaches are also ideal sites for the second dating method attempted, that of thermoluminescence dating of sediments. Thermo-luminescence (TL) dating requires sandy material (preferably quartz rich) that has seen sunlight then been buried, such as in a beach ridge. Samples were taken in the sandy ridges and in one site where there were shells, a TL sample was taken alongside. Having the two dating methods in the single place should allow a correlation between the dates obtained. The method for collecting TL samples was changes very little to adapt to Antarctic conditions. Site selection was important as it was impossible to drive a tube to collect sediment into permafrost. A block of wood to place over the end of the tube that could be pounded into slightly frozen ground was useful. We found that if a hole was dug that was suitable, yet frozen, often waiting a day to allow some thawing of the surface layer was enough to get a tube into the sediment. When taking dose rate readings with the gamma spectrometer, to get the probe far enough into the sediment required the use of a small portable hand auger.
The main method of dating used was surface exposure dating using cosmogenic isotopes in the rock platforms associated with the beaches. Cosmogenic isotopes record the build up of cosmogenic radiation from hitting the Earth's surface. If a site has been eroded then exposed at the surface it will start building up the isotopes from the time it was exposed. By collecting surface samples of rock (preferably calcite or potassium rich rocks) a
No results have been obtained so far on any of the dating methods as the samples are not back from Antarctica at the time of writing, but the surface exposure dating appears to be a promising tool for recording uplift.
Detailed descriptions were made from sections, using evidence at the surface as well as digging holes in strategic locations. It would have been nice to have trenches through the ridges, as may be possible in a temperate environment, but frozen ground did not make this possible. An essential tool in many holes, where digging below the permafrost level was desirable, was the use of a poinjar. This worked effectively to remove material, otherwise various shovels, spades and picks were employed. Along this part of the coast the permafrost level is about 0.5 m, but is extremely variable with water being struck in one hole. Information from the holes included the structure of the beach ridge, pebble counts to work out maximum energy and development of the beach from imbrication. Indications that there was little, if any, ice influence in most of the beaches could be seen by a lack of ice features in the holes.
Where holes were not dug surface pebble counts gave approximations to the same things. Holes were not able to be dug where the whole beach ridge was boulders. Other large scale measurements were made such as cusp sizes. Profiles of high energy sites and lower energy sites were made for comparison.
Measurements of the same features on the active beaches provided a basis for comparison to the raised beaches. After the sea ice broke out there were opportunities to watch the beach processes in action with waves and ice. Earlier, it was attempted to use an underwater camera to observe any processes occurring while there was still shore attached ice. This was not particularly successful but it is believed that the ground is covered in ice at this stage and not active. Future work, next season, will include a lot more process observations and measurements of the open water conditions.
Observations of the glacial moraines were done by mapping the extent of the various rock types that made up the moraines by a combination of noting where volcanic erratics were found with line counts and area counts. Surface
Preliminary observations from the extent of volcanic erratics (derived from Ross Island and further south) indicate that the Ross Sea ice mass extended up to ~350 m altitude on Hjorth Hill above Cape Bernacchi, it also covered Marble Pt and Spike Cape. These observations place the limit of Ross Sea ice a minimum of 20 km further north than that previously reported (Hall and Denton, 1994. Antarctic Journal pp 20 - 22).
Moraine deposited by the Ross Sea ice appears to be significantly older, based on weathering and appearance of striations, than moraine deposited by the Wilson Piedmont Glacier. This implies a more recent advance of the Wilson Piedmont which may have overrun earlier Ross Sea moraine.
Future work intends to extend this work further along the coast, which will give an overall picture of the way the coast is rebounding with distance from the Ross Ice Shelf. Studying the beaches on Ross Island, and possibly Beaufort and Franklin Islands will enable a test of the source of the ice causing the isostatic rebound. There may be an isostatic response to expanding local ice on the Victoria Land Coast as well as to grounded ice in the Ross Sea. The beaches on Ross Island have a longer ice free season than elsewhere so will not only provide a comparison on levels of development, but also allow process measurements to be made over a length of time.
There are intentions to publish results from this work. Below are the topics that should become papers.
Expansion of the Ross Ice Sheet over the Scott Coast during the Last Glacial Maximum.
Antarctic Beach Geomorphology.
Alternative Dating Methods on Antarctic Beaches.
Further publications will result as this seasons and next seasons work are combined.
This event was supported by funding from The Australian National University in collaboration with Victoria University of Wellington. Edward Butler is being supported by a New Zealand Post Antarctic Science Scholarship. The support of event K191, the survey team from Terralink NZ Ltd were very helpful in placing benchmarks. The Quaternary Dating Research Centre at the Australian National University lent their gamma spectrometer for use with the thermoluminescence dating. The Antarctic Research Centre at Victoria University of Wellington lent their GPS equipment and underwater camera.
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.
Data surveyed by Belgrave, Cairns, and Simonsen 4 Dec - 10 Dec, 1996.
The accuracy of the positions stated by Belgrave (pers. comm. 1997) is as follows:
Maps on the following two pages were compiled and drafted by Ian Jennings.
Approximately 800 pounds of equipment was shipped from Wellington to Antarctica prior to the event. All equipment arrived on schedule and was found to be in good condition at Scott Base. Major pieces of equipment included:
Because Jon DeVries was involved in field training with the event personnel, it was possible to cover exercises that were directly applicable to the conditions relevant to the field area of the event. Day one of Antarctic field training followed the standard exercises, but the use of fixed ropes on the steep rocky terrain of Observation Hill was covered on day two.
All of the drilling equipment was assembled, tested, and checked out in the vicinity of Scott Base. All other equipment (tents, radios, stoves etc) was checked at Scott Base and was fully operational before departure to the field.
Generally all of the necessary field equipment was at Scott Base and in good working condition. All equipment was thoroughly checked before the event left for the field. Two of the primus stoves, which were issued, were found to be faulty. Of note is that one of them was brand new and had a faulty thread (manufacturing fault) where the burner screws into the fuel tank. This fault was not obvious and only showed up when the stove was hot which caused the thread to loosen and bleed off gas pressure.
The Polar Haven tent was a real bonus on this trip and made it possible to have a warm communal area for cooking and discussion of the day's events. In this particular case, we only set up camp once for the duration of the field season. The following points should be taken into consideration when using a Polar Haven:
Due to the nature of our field event which involved constant use of drilling gear, we requested extra spill kits and a tarpaulin to minimise environmental damage which could result from leaking oil or gas. However, we were only able to get one very old canvas tarpaulin and one extra spill kit (small size) before deployment. We finally acquired the large size, spill kit refills three days before returning to Scott Base.
To minimise the risk of environmental damage from this type of project, any machinery which is likely to have oil or fuel leaks should if possible have a drip tray. Further protection could then be given by the use of a tarpaulin.
One of the 20 litre containers of kerosene was contaminated with mineral turpentine which appeared to cause incomplete combustion in the primus stoves. All fuel containers 10 litres or larger should be able to either be fitted with a spout or a tap. All human waste needs to be triple bagged to be safe for handling and transportation.
On the whole helicopter operations ran smoothly once schedules had been worked out. Our main camp moves and some of the drill site moves were done with the 3 Squadron UH-1H and went very smoothly and efficiently. There was a one day delay, due to weather, for our pull-out of the field.
The set-up in the BH 212, with the rear facing seats and the permanently fitted auxiliary fuel tank, limited its effectiveness when it came to moving cargo as an internal load. The other problem with the rear facing seats was that it was difficult to give the pilot directions when trying to locate a landing site for close support work. The lack of any ground to air communication with the BH 212 made it difficult to work with when the helicopter was approaching our camp or drill site and when moving drill gear from site to site.
For a moderate sized event such as this one, it was extremely useful and efficient to have a spread-sheet with all the helicopter loads for the put-in (Table 1). This information was also made it much easier to figure out loads for the pull-out. A copy of Table 1 was given to Rex Hendry.
After initial problems with an intermittent transmitter, communications with the Tait handheld radio and high-gain aerial, using the Mt Newall (Ch. 5) repeater, proved to be reliable from our camp site. High frequency communication was not successful from our location. The Tait radios were also used for communication between team members away from base camp.
In general the transfer of requests and information given over the radio were passed on to the appropriate people at Scott Base. However, on occasion this did not appear to happen. The format of the scheduled radio check-in was at times inconvenient for our event because we were still drilling. On numerous occasions when contacted for the evening check-in we explained our situation and requested leave of the weather and news. This was noted and given approval by the base operator. Then after the reading of the new and weather, we would be repeatedly called until we acknowledged the weather and news. This situation would not have been a problem except that we had to again stop work and go to the closest high point to transmit. A solution to this problem would be for Scott Base to contact all field parties and then pass on the weather and any messages to all parties, get an acknowledgment, and then anyone who wanted to listen to the news could do so. However, I believe the news is an important part of the communications set-up and should be continued.
The quantities of food taken into the field were certainly adequate. With the addition of the extra food (tortillas etc.), which the event supplied, there was a good variety. Unfortunately, we didn't count on the meat eating appetite of the ravenous hell driller from the West Coast. Only major complaints were not enough cheese due to a supply problem, and too many munchy bars which was our fault.
If the same system is used down to a depth of nine metres and at higher altitudes, the motor for the drill rig needs to be larger because it was working at its maximum capacity at 2000 metres. The Stihl 056 motor which was used to drive the compressor would probably be suitable. This system also needs modifications to the air cooling system. The simplest of these would be to extend the air intake away from the warm air environment created by the compressor.
The Winkie Drill tripod supplied by ANTNZ was also used beyond its safe working load at these depths. Unless the legs of the tripod can be braced at mid-height, the leg with the attached winch will bow out dangerously. The loading on the tripod was also increased by the addition of a block in the system to give a 2:1 ratio. The winch on the tripod is reasonably
Any project which involves the use of machinery has industrial type risks. The project was completed without any injuries which is a reflection of the teamwork and competence of those involved in the project. The only medical problem was an pre-existing eye condition, which could have been aggravated by the exhaust fumes from the drill motor. Some thought needs to be put towards the modification of the exhaust system of the drill rig if the same system is used in the future, the exhaust system needs to be modified so that it is vented away from the drilling personnel. There is also a risk of burns from the present exhaust system.
A recommendation for future projects of this nature is that all personnel involved in drilling should wear steel capped Sorrels and safety helmets with attached grade 5 hearing protectors.
All party members were either in visual or radio contact at all times when we were doing field work on Table Mountain. The area covered during the time in the field was relatively safe terrain.
In general, weather conditions at Table Mt were mild enough to allow field work nearly the entire time (Table 2). However, the conditions were often very localised with warm coastal air masses moving up the Ferrar Glacier and cold Polar Plateau air masses flowing down the glacier. When these two air masses met in the Table Mt area, they would cause a local build-up of Stratus or Stratocumulus clouds. This would commonly occur from mid morning to late afternoon. This weather pattern occurred about 30% of our total time in the field. These conditions would sometimes result in light snowfall.
During the field season, no winds above 25 knots were experienced even though reasonably strong katabatic winds could be seen and heard blowing down the Ferrar and Tedrow Glaciers. The wind was predominantly 5 knots from the south west.
The main goal of scientific research for the project is to understand depositional and post-depositional history of 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. In the debate, the dynamic view, which relies on the occurrence of rare marine diatoms in the Sirius, favours a nearly complete deglaciation of the East Antarctic ice sheet three million years ago. On the other hand, the stabilist view favours an ice sheet which formed nearly 14 million years ago and retained its shape through until the present day. Cores from within the Sirius will provide information not available from surface exposures that will help resolve this debate.
The goal of the field work was to test a diamond drilling technique and core as much as possible of the Sirius at Table Mt. During the 23 days in the field, a total of about 49 metres was drilled, and 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 them reached depths of 9.5 and 8 metres. In addition, detailed glacial fabric analyses of the Sirius were made at 12 sites and enough geologic and geomorphic data were collected to provide a detailed map of about four square kilometres on the northwest flank of Table Mt.
Sirius Group deposits on Table Mountain appear to result from both advancing and retreating glaciers. Ice retreat 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 is dominated by water-lain deposits of which the conglomerate and sand suggest that both high and low energy regimes were involved.
Petrographic analysis shows that authigenic zeolites, quartz, and calcite occur in various quantities throughout the pore network of Sirius sediments. Pores near the surface appear to result from freeze-thaw processes associated with periglacial activity, while those below three metres formed as the sediment was deposited. For authigenic minerals to precipitate, large volumes of water must have flowed through the pores. While this is inconsistent with present climatic conditions, the large amount of water is consistent with geomorphic observations and deposition of the sandstones and conglomerates. It is also consistent with the significant amounts of ice found in the pores and fractures of the core. Stable isotopic measurements of this ice may help determine the origin of this water.
In the future, more diamond coring of glacial deposits in the Dry Valleys area is needed to provide a detailed history of the Antarctic ice sheet. Modification of the core drilling equipment used in this project will make it lighter weight, more reliable, and allow a variety of sites to be cored in a single season.
The aims of the field work and subsequent research, as established by the PGSF grant in December 1995, were as follows:
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.
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.
Core drilling of permafrosted sediments is common and well understood in most Arctic environments, but in the cold, dry
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.
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
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.
As event leader, my most sincere appreciation and thanks are given to the five other members of the event who were largely responsible for the success of the field season. All of the personnel at Scott Base were extremely helpful and provided the support that made the field season possible. In particular, Paul Woodgate in Christchurch and Bridget Troughton at Scott Base were extremely efficient in shipping extra drilling equipment at the last minute. Numerous discussions with Alex Pyne greatly helped in organizing the field season. Graeme Claridge provided much needed background information as well as the spark that initiated the diamond core drilling. Nine metres of drill rod provided by Jim Cowie and the Cape Roberts Project made the drilling eight and nine meter holes possible. Jeff Ashby gave much needed assistance with the drilling reports, and Peter Barrett saved the PGSF bid from going under in the early stages. Funding for the event was provided by the Foundation for Research, Science and Technology under contract number DIC601.
Small cairns of one to two cobbles high were left to mark and cover open core holes at TM-1, TM-2, TM-6, TM-7, and TM-8 (see locations on drill hole map). These holes were left open for future monitoring of ground temperatures. In addition, it may be feasible in the future to deepen the hole at TM-7 to penetrate through the Sirius to the underlying bedrock contact.
The main impact at the Table Mt sites consisted of tramping over the fragile desert pavement. While this is unavoidable if field work is to be conducted in the area, such an impact is visible for perhaps 5 to 10 years after the event. This is because of slow the process by which the pavement forms. When working around a drill site, event personnel attempted to follow the same track. When the drill site was vacated, pavement stones were swept and raked over the tracks in an effort to reclaim the surface. In most cases this mitigation measure, significantly reduced the visual impact and should allow the pavement to reform completely in 3-5 years.