IMMEDIATE SCIENCE REPORT
K047: Climate and Landscape History from shallow Drilling in the Dry Valleys
Antarctica New Zealand 2000/01
1) Popular Summary of Scientific Work
This project is based on new portable drilling techniques which allow shallow coring of permafrosted glacial sediments in remote areas. The primary aim of this project is to recover a climate record from Antarctic ground ice and soils, which potentially hold detailed records that date back to 15 million years ago. The cored material will not only be used to determine climate and climate history from geo and biochemistry but will also provide stratigraphic information for ground penetrating radar studies and outcrop maps of glacial sediments.
One of the main scientific problems to be addressed by this project is the origin of ground ice at high elevations (<1000m) throughout the Dry Valleys of Antarctica. The origin is unclear because there is no obvious contemporary source of water. Three possible sources have been proposed: 1) The water came only with the original deposition of the sediments, 2) additional water was introduced after deposition during an undocumented warm period in Antarctic history, or 3) additional water has condensed from atmospheric vapour, which has diffused into the ground over millions of years. Preliminary work suggests that mechanism three is applicable and that this may be similar to the occurrence of water on Mars.
2) Proposed Programme
The main technical objective of the season was to test the capabilities and design of the refurbished Winkie drilling system which was modified for air coring. Along with this objective, there were three scientific objectives: 1) to provide a series of shallow (2 m) cores to assess the degree of contamination of diesel drilling fluid around DVDP-6 (drilled in 1972), and to locate and re-enter this hole to assess its current status; 2) to provide stratigraphic cores of the Sirius Group at Allan Hills and Mt Feather for thickness and facies analyses; 3) to provide shallow cores for comparative age analyses by Be and N inventory of three different aged deposits (Sirius, Sirius regolith, and debris flow) at Table Mt and deployment of 2 m thermistor probes in two of those deposits which have pattern ground.
3) Scientific Endeavours and Achievements
Nine holes and 15.90 m of core were recovered from a grid pattern of drilling around DVDP-6, and they suggest that the diesel drilling fluid used in 1972 only penetrated the active permafrost layer to a depth of about 0.6 m. In addition, DVDP-6 was relocated, cased to a depth of 12 m, and capped. At Allan Hills (Trudge Valley) two holes and 8.20 m of core were recovered showing that the Sirius consists of a thin veneer (4-5 m) in the valley bottom and that it is ice-free to a depth of 1.5 to 2.5 m in this area. Coring did not reveal any new facies of the Sirius at Allan Hills. At Table Mt, six holes and 18.67 m of core were recovered. The cores revealed a new fluvial gravel facies of the Sirius and showed that depth of polygonal ground may extend deeper than 6 m. The two thermistor arrays were deployed in different polygonal ground and set to record temperatures (12 cm intervals to 2 m deep) 4 times a day for 11 months.
Dickinson and Pyne spent 39 days in the field and 5 days at Scott Base. Of the field days, 9 (includes one no-fly Sunday) were spent waiting on weather to clear. An additional 3-4 days page break were lost to technical problems with the drilling system. In all, 17 holes were drilled in three areas, Lake Vida, Allan Hills, and Table Mt and a total of 42.44 m of core were recovered for 48.44 m drilled.
|1)||Core bits need further testing and design. With the present system, the clearing of cuttings, and in particular ice-rich cuttings, becomes more difficult with depth below about 2 m. Unless this problem is solved, holes deeper than about 10 m are not practical with this system as reaming is required below 6 m.|
|2)||The compressor system generally worked well, but consumes a lot of fuel and requires a dedicated operator. Modifications are required to the protective box so that the compressor and its coalescing filter can operate in a warm and uniform temperature. It may also be possible to reduce fuel consumption if demand air flow can be regulated.|
|3)||Cooling of the compressed air is required and drilling in temperatures above −3°C is probably not practical. In addition, moisture from compressed air must be removed before entering the cooler. With the present system it is not practical to drill in either cloudy or snowy conditions because of ice build up in the air ways.|
|4)||Unquestionably a drilling shelter is needed for winds greater than about 7 knots. However, the present shelter and platform can be lightened in weight and simplified in design to increase set-up and break-down time.|
|5)||A drilling camp of at least 5 people is required to support the present drilling system. The camp, drilling system, and fuel (five 12 hour days of compressor operation) translate into 6 helo loads (3 internal and 3 sling). The logistics of such moves are complicated and demanding on Antarctica NZ resources and suggest that one and possibly two areas can only be drilled in a season.|
Scientifically, much was accomplished during the field season, however, the initial objectives outlined above were extremely ambitious in view of the fact they were set before the capabilities of the drilling system were completely understood and tested under Antarctic conditions. Site selection for coring is critical and must be reviewed by both scientists and drillers prior to conception of logistical plans. The depth to ice-cemented sediment must be determined so that if necessary casing can be provided and used during coring. Core recovery in ice-free sediments is probably not possible and if this zone cannot be cleared by shovel it must cased off, if drilling below this zone is required. In logistics planning, allowance for bad weather is critical because of the time needed for 6 helo moves. November 2000 was one of the snowiest on record at Scott Base and given the variable conditions in the mountains, the weather must be suitable both at base and in the field for helo movement to occur.
At Allan Hills 2 core holes were drilled in Trudge Valley (Fig. 1). The site initially selected was on the top of the 'ramp', but high winds made drilling at this location impractical for field time allotted to the Allan Hills area. Therefore, to assess the thickness of the Sirius in Trudge Valley, we decided first to core the Sirius outcrop on the valley bottom NE of the 'ramp'. To our surprise, we found the top 1.5 m of Sirius was ice-free and core from this page break section was lost. At this hole, the Weller was encountered at a depth of 3.40 m. It was decided to drill the second hole in Trudge Valley in the basal part of the 'ramp' sediments which overlie the Sirius. The idea was that the top of the ice-cement would lie in the 'ramp' sediments and allow recovery of a complete section of the underlying Sirius. Unfortunately, the unconsolidated 'ramp' sediments made drilling extremely difficult and slow. Consequently, the first core recovered at a depth of 2.48 m was the Sirius, and it was not possible to core the contact between the 'ramp' sediments and the Sirius.page break
A move to other sites in the Allan Hills area became impractical because of time constraints. Persistent 30 - 40 knot winds on the Upper Triangle essentially ruled out access to this area. Good outcrops surrounding the Lower Triangle and the probability of a thin Sirius section due to the 1-2 m thickness of the ice-free horizon, ruled out coring in this area as well.
At Table Mt, 6 core holes were drilled in an area where a ridge of Sirius is truncated by a debris flow of dolerite blocks which is marked by large (15 m across) polygonal ground (Fig. 2). Adjacent to the ridge is the Sirius regolith which is marked by small (5 m across) polygonal ground. These three outcrops are within a 100 m radius so a helo move of the compressor was not necessary. The primary objective was to take 3 m deep cores in each of these outcrops for Be/N inventory dating. The secondary objective was to investigate the nature of the polygonal ground and determine the depth of the 'active' layer. In this case, the term active layer does not refer to annual freeze-thaw, but the depth to which the polygonal ground extends. In the large polygons, 3 holes were drilled; one in the centre, one at the perimeter and one half way in between these holes. Due to the blocky nature of the debris flow, depth to the ice-cemented horizon varied from about 10 to 45 cm. TM-00-1 drilled in the centre of a polygon terminated at a depth of 6.3 m due to a stuck and un-recovered bit and core barrel. TM-00-2 was drilled half way between the centre and perimeter of the polygon to a depth of 2.37 m so that a 2 m thermistor probe could be installed in this hole. The hole at the perimeter, TM-00-3, was drilled to 2.70 m and terminated when drilling became difficult.
TM-00-4 was drilled at the top and southern-most end of a kilometre long ridge of Sirius (Fig. 2). The ridge is mostly capped by the dimict facies of the Sirius which overlies the well sorted sandy facies of the Sirius. The surface of the ice-cemented horizon at 48 cm was very even and flat which probably reflects the homogeneous nature of the sandy facies. Coring was fast (1 m /0.5hr) and drilling was terminated after 3 runs at 3.21 m.
A small polygon in the Sirius regolith was cored in its centre and perimeter. Depth to the ice-cemented horizon was less variable than in the large polygon and averaged about 15 cm. In hole TM-00-5 at the polygon centre, ice-cemented dolerite clasts (10-20 cm diameter) were present to 1.03 m deep where the well sorted Sirius sand was encountered. This may represent the depth of the active layer. Unfortunately, coring was terminated in a large dolerite clast (only known to be a clast after drilling the perimeter hole) at 1.83 m after drilling only 0.3 m in 1 hr. The perimeter hole, TM-00-6, encountered the sandy Sirius facies at about 0.88 m. However, at about 1.47 m a gravelly facies probably of fluvial origin was encountered. This facies continued to 4.40 m when coring was stopped for the move back to Scott Base.
|1)||Because of the weather in November and early December as well as the constraints on the drilling system, which were only determined during the field season, it was felt that at least 12 to 14 field days were required to complete an estimated 10 to 15 m deep hole through the Sirius Group at Mt Feather. Even though there were no helo moves within the Allan Hills area, we were still only able to leave for Table Mt on 7 December. With this late a departure, the required time at Mt Feather was simply not available in this field season.page break|
|2)||With the drilling system, field camp and personnel, at least 6 and probably 7 helo loads would be required for K 047A to put in at Mt Feather. This was beyond the helo support which Antarctica NZ was prepared to give K 047A for the season. Although the exact helo hours used are not yet available, K 047A was allotted 33.1 hours for the season and 11.5 hours were used to move K 047A from Marble Pt and Lake Vida to Allan Hills. An additional sling load of fuel would probably have been necessary to complete the drilling at Mt Feather.|
Collecting Endoliths at Battleship Promontory
On Monday 4 December 2000, helicopter HNO from Allan Hills unloaded Alex Pyne, Warren Dickinson, Wayne Pollard and Glen Kingan at approximately 10:15 am with emergency camp gear. Stratus cloud was at about 4/8, wind <3 knots and variable, and temperature was about −6°C. The helo returned from Marble point for pickup at about 12:45. During this time, cloud cover increased to about 7/8 but winds had remained about the same.
Endoliths with bright green colour were patchy in their habitat and more difficult to find than anticipated. Unfortunately, only 2 hours had been allotted for sampling, and due to sample variability, probably 3-4 hours were needed to collect the required amount.
Endoliths were found both in fractures and as a consistent layer about 5 mm below the surface in the more porous and weathered sandstone of the Beacon Heights Orthoquartzite. However, during the collection time an understanding of the most favourable growing conditions of the endoliths was not determined. To sample as efficiently as possible in the restricted time frame, tasks were divided as follows:
Warren Dickinson searched for endoliths with a geo pick and recorded notes on the collection. He also too 35mm pictures and digital video of the operations. Wayne Pollard, using a geo pick, searched the wider area for endoliths. Glen Kingan also searched for samples and used the kanga hammer for splitting large samples which were brought to Alex Pyne for processing. Alex Pyne, with two layers of latex gloves on, sized the samples with a small chisel, and bagged and labelled them.
The endolith samples were taken from two areas about 30 m apart and from numerous sites of boulders or slabs the size of which are listed in the following table.
|Area #1 (photos 4-7, 4-8, 4-9) about 150 m from helo landing|
|Site #||Rock Size (mm)||Comments|
|2||200x100x100||Endoliths in small fractures|
|3||200x150x100||North facing boulder w/smooth face|
|Area #2 (photos 4-10, 4-11) about 30m SE of area 1|
|4||250x250x100||weathered & friable|
|5||---||weathered & friable|
|6||---||weathered & friable|
|7||---||highly weathered and pock-marked|
|8||1000x500x500||hard but few fractures|
|9||1000x500x200||crumbly and fractured|
|10||500x400x300||hard red horizon, surface is platypage break|
|11||---||surface crust over hard ss|
|12||1000x750x100||slab is very rich in endoliths|
|AREA||HOLE #||DATE||START DEPTH (m)||TOTAL DEPTH (m)||TOTAL CORE RECOVERED (m)|
|Allan Hills (Trudge Valley)||AH-T-1||24-26/11||0||4.23||2.30|
A preliminary report on the shallow drilling methods and core results will be published as an Antarctic Research Centre Report in June 2001. This report will include much of the technical work on the drilling system, core logs and photographs, maps and cross sections. Copies of this report will be sent to Antarctica NZ.
Further publications of the scientific results will be published in international peer-reviewed scientific journals. Copies of this work will also be sent, when available, to Antarctica NZ.
- Prof Peter Barrett, (Director, Antarctic Research Centre, VUW)
- Dean Peterson, Paul Woodgate and Pete Cleary, (Antarctica NZ)
- All of the Scott Base personnel (Nov 2000 - Jan 2001)
- Bill Gilmore and Kirsty Wade (Raytheon Polar Services, USA)
- Bain Webster and Jeff Ashby (Webster Drilling Inc, NZ)
- Prof Joe Trodahl and Eric Broughton (VUW)
- Antarctica New Zealand,
- Strategic Development Fund, VUW
- Netherlands National Science Foundation
- Foundation for Research and Technology, NZ
- US National Science Foundation, USA
- Webster Drilling Inc, NZ