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Victoria University Antarctic Research Expedition Science and Logistics Reports 1978-79: VUWAE 23
SCIENTIFIC ACHIEVEMENTS
SCIENTIFIC ACHIEVEMENTS
Transport of glacial debris (Paul Robinson)
A week in late October 1978 marked the end of sedimentological and glaciological field work for the Taylor Glacier project. Paul Robinson and Stewart Ross (DSIR) made an early season trip to Taylor Glacier (Plate I) to complete the englacial sediment sampling and to observe englacial structures before the 'melt' began. This was followed by two weeks (Oct 28-Nov 11) investigation of dry valley alpine glaciers (Rhöne, Sykes, Albreich and Sandy) and two outlet (?) glaciers (Wright Upper and Victoria Upper). Comparisons of the englacial sediment texture, ice structures and the products of deposition indicate that the mechanisms of debris incorporation for these glaciers differ from those of Taylor Glacier. Rhöne, Sykes, Albreich, Sandy, Wright upper and Victoria upper (Plate II) Glaciers contain various types of glacial debris, but none show the strong basal character of Taylor Glacier.
Taylor Glacier sediment ranges in sizes from clay through to large boulders, and is presently depositing this boulder-clay (or till). The percentage of sediment on the ice ranges from less than 1 to 60 per cent, and this, together with the various sediment grain size textures, gives a good indication of the modes of debris incorporation. The predominant process for Taylor Glacier sediment entrainment appears to be basal regelation. This probably occurs 1) by abrasion, pressure melting and the associated "freezing in" of debris at the glacier sole; and 2) by block incorporation of pre-existing till, again by freezing of meltwaters at the base of the ice mass. Although both of the above processes produce similar sediment texture, the sediment to ice concentrations vary (abrasion and regelation less than 1 to 20 percent; till block regelation commonly greater than 15 to over 60 per cent).
The alpine glaciers (including Wright Upper and Victoria Upper, which were previously considered true outlet glaciers) contain diffuse (generally less than 5 per cent sediment to ice), moderate to poorly sorted, angular to subangular sand and pebble debris (Plate III). Such sediment is characteristic of a supraglacial origin, where valley wall rock fall is buried by snow accumulation and subsequently transported englacially.
This project reveals the apparent uniqueness of the Taylor Glacier in comparison to other glaciers terminating on land in the Dry Valleys. However, future observations of glaciers such as the Ferrar, MacKay and Mulock, all plateau-fed glaciers, may reveal an ability to produce basally-derived debris.
Zones of net basal melting and refreezing for the inland ice (Drewry, in press) and Taylor Glacier (Robinson, in prep.) have been determined from geophysical and glaciological data. This is consistent with the already outlined basal debris regelation model. However, for the sediment presently being deposited at the snout of Taylor Glacier incorporation would have to have occurred between 2000 and 6000 years before present. This is based on estimates of present day positions of basal sediment incorporation sites, and assumes present day ice velocities.
Glacial sediments surrounding Taylor Glacier and Lake Bonney exhibit similar features to the englacial material of Taylor Glacier. Therefore, it seems likely that the main process of debris incorporation by Taylor Glacier has been basal, and that Taylor Glacier is, and has been, a wet-based glacier for several thousand years.
The saline discharge at the snout of Taylor Glacier (Black, 1969; Keys, in prep.) was underway during the October visit (Plate I). Temperature measurements of air (−26 to −16°C), ice (−17 to −10°C) and the liquid discharge (−6 to −5 5°C) were made. An estimate of the total discharge was considered to exceed 3000m3.
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While working around Wright Upper Glacier an in situ outcrop of granitic basement was located (Plate IV). Exposure is restricted to 0.5 km2 in the N.W. corner of the Labyrinth, but appears to extend under the N.E. margin of the Wright Upper Glacier. Here the Labyrinth dolerite sill has thinned out, so that the overlying Beacon sediments are in direct contact with the granitic basement. These observations are in direct contrast with Claridge and Campbell, 1978. They suggest that no granitic material is exposed west of Koenig Valley, Asgard Range. This previously undescribed outcrop may have significant bearing on the inferred direction of ice movement (Robinson, in press).
In conjunction with Event 1 (Dry valley hydrology), Robinson spent two days at Wright Lower Glacier. Attempts at locating glacier ice beneath lake ice were abandoned when drilling equipment was damaged by coarse sediments 2 m down at the probable lake ice glacier ice contact. Further attempts were to be made later on in the season by Event 1.
References
Black, R.F., 1969. Saline discharge from Taylor Glacier, Victoria Land, Antarctica. Antarctic Journal of the U.S. vol 12 (4): 102-104.
Claridge, G.G.C. and Campbell, I.B., 1978. Moraines of probable Miocene age, dry valleys, Antarctica. N.Z. Antarctic Reocord 1 (2): 1-5.
Drewry, D., in press. Geophysical investigations of ice sheet and bedrock inland of McMurdo Sound, Antarctica. Antarctic Geoscience (C. Craddock, ed.). University of Wisconsin Press, Madison.
Keys, J.R., in press. Some saline and glaciological studies in the McMurdo Sound region. PhD Dissertation.
Robinson, P.H., in press. Eastward ice advances in Wright Valley, Antarctica. N.Z. Antarctic Record. 2 (1).
In preparation - An investigation of entrainment, transport and deposition of glacial debris by polar ice, with special reference to Taylor Glacier, Antarctica. PhD Dissertation.
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FIG. 2. Map of New Harbour showing the two drill sites investigated. The bathymetry presented by Barrett, Treves et al. (1976, Fig. 2) is shown as dashed contours. The bathymetry obtained from the site survey of November, 1978, is shown by cross-sections (MSSTS 1) and a heavy contour (MSSTS 2).
Physical characteristics of MSSTS Sites 1 & 2 (Peter Barrett and Phil Bentley)
The purpose of this part of VUWAE 23 was to locate and determine the physical conditions at the two sites proposed for drilling in late 1979 in western McMurdo Sound (Fig. 1). For each site local bathymetry was determined and an access hole then opened for current measurements and sea floor sampling. Nothing was found at either site to suggest that drilling should not proceed.
The 1978 winter was unusually cold and the sea ice thickness greater than expected. Around site 1 the thickness ranged from 2.5 to 2.8 m, though the ice must have formed that year. At Site 2 the thickness was 4.0 m and the two debris layers in snow patches on the ice surface suggest the ice was entering its 3rd season. We had hoped to determine water depth by using a depth sounder and placing the transceiver (the energy source) on the sea ice surface in a puddle to minimise energy loss. Neither of our tow instruments (SIMRAD, frequency kHz, power watts; FURONO, frequency 50 kHz, power 10 watts) displayed a return signal, and we found it necessary to drill a hole through the ice. On some occasions a signal was received when the transceiver was only 1 m down the hole, but on others no signal was received even when the transceiver was lowered to the base of the ice. When a signal was received the depth indicated was within 2% of that obtained from a line. Because of the uncertainty of the depth sounders, and the need to drill a hole through the ice anyway to obtain a depth, we opted for the time-honoured (and time-consuming) method of the weighted line. However, there is no doubt that a depth sounder that could operate through the sea ice would be a major advance for marine scientists using sea ice as an operating platform; Physics and Engineering laboratory, DSIR, are currently investigating ways of improving commercial depth sounders for such an operation.
The bathymetry in the region of MSSTS Site 1 (Fig. 2) shows a shelf at 180 to 200 metres over a large area with a dome close to the proposed drill site. Both major northwest-trending lines were expected to encounter a 300 m deep valley revealed by previous surveys (Northey et al., 1975, Figs. 2 & 3), though it could lie between two stations, which are about 1 km apart for much of the survey. The dome, which rises to less than 120 m below sea level is an odd feature of unknown significance. It could be a volcanic core or reflect a basement high or be one of several other possibilities. In any event it is suggested that the drill site be moved about 2 km to the southwest so that a flat (typical) part of the sea floor is drilled. The bathymetry at MSSTS Site 2 is simple (Fig. 2) and indicates a basin with a maximum depth of a little over 110 m.
We planned to cut the access holes with chain saws and to break out the last few 30 cm or so with crowbars and heavy chisel points attached to SIPRE rods. At Site 1 it took 8 hours of very hard work to make a hole 1.0 × 1.2 m × 2 m deep, by which time we were not at all reluctant to use eight pounds of explosive (2 in each comer) to finish the job. However, one of the holes for the explosive penetrated the bottom filling the excavation with sea water. The nearby tent proved to be too close (Plate V). No damage was sustained, but the sleeping bags were uncomfortably wet, and were almost impossible to dry properly. At Site 2 we cut a hole 1 m deep and sliced the ice below this for a further 0.8 m. Four 4 lb charges were used, and another small charge was necessary to break a hole 1.5 m across through the 4.0 m thickness of ice. A third access hole was attempted at the snout of Ferrar Glacier using a single 30 lb charge three-quarters of the way through the 4.8 m thick ice. This shattered the ice reasonably well but the hole was not large enough to use the grab for sea floor sampling.
Current measurements were carried out every three hours over a 24 hour period at both drill sites and at Ferrar Glacier snout using rotors (Plate V) borrowed from the N.Z. Oceanographic Institute. The meter was read half way down and 1 m above the sea floor. Before the rotor was lowered, it was moved in the water to check that a signal was reading in the meter. No currents were recorded, indicating velocities less than 2.7 cm s-1.
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Sea floor sampling with a McIntyre grab (Plate VII), also borrowed from the N.Z. Oceanographic Institute, produced much more positive results.
Sampling was successful about two times in three, with the sea floor sediments filling about two-thirds of the grab. The sea floor itself was little disturbed, and at Site 1 showed a varied fauna (Plate VIII), in addition to a dense muddy mat from 1 to 5 cm thick of sponge spicules. Site 2 had very few creatures by comparison. The sea floor was well preserved by subsampling with a metal box and storing in plastic containers (Plates IX and X).
The texture of the sea floor sediments at both MSSTS Sites 1 and 2 is moderately sorted medium to coarse grained sand with admixtures of gravel (<4 mm) typically from 0.3 to 0.8% and of mud from 3 to 13%. The gravel fraction from both sites includes both granitic and basaltic stones, though the latter which include both floor rocks and tuffs, are dominant. Of particular interest are pieces of light olive grey claystone, possibly from early Cenozoic Strata. The sand fraction appears far more distinctive at each site, being basaltic at MSSTS Site 1 and quartzo feldspathic at Site 2 (New Harbour).
An important feature of the sediment is the burrowing, seen in Plates IX and X. As the grab samples were washed for pebbles, mucus-cemented sand tubes collected in the sieve and were disaggregated only with some effort. The tubes are best seen as the sediment surface in Plate X, but occurred in abundance at both sites. The faint mottling in the section of Plate X is also an indication of burrowing. We were not able to determine how far beneath the sea floor present day burrows extend, but they are commonly 8 cm long and this may therefore be taken as a minimum. We noted above that the sponge spicules at Site 1 were abundant only in the upper few centimetres. Perhaps their paucity beneath is due to comminution by burrowing organisms.
Sediment on ice-bergs and sea-ice in western McMurdo Sound (Peter Barrett and Phil Bentley)
Sediment on the sea floor in polar regions has three main origins - floating ice, wind and biogenic production. Part of the VUWAE programme this year was to investigate sediment in transport today by wind and ice in western McMurdo sound.
Ice-bergs are a common feature along the western shore of the Sound. Most are floating and are trapped in the sea-ice, but several large bergs, many to 80 m above sea level, have grounded for some years near the site of DVDP15 (Barrett and Treves, et al. 1976, Fig. 2). Most of the bergs have no visible trace of glacial debris, although patches of wind-blown sand are quite common. This year, however, one small and two large ice-bergs were found in the New Harbour area with a continuous thin (0.3 m) cover of rock debris clearly destined for the sea floor. The largest (Plates XII and XIII) reached a height of about 20 m above sea level and was about 1 km long.
From our examination of the debris we concluded that it accumulated on the surface of a glacier that reached the coast and calved. There are a few abraded and striated pebbles, which must have had a basal glacial origin, but most are angular, which, together with the lack of mud-sized material, indicates a superglacial origin for most of the debris. The ice beneath the debris layer appears to contain no debris itself and therefore can not be the source.
A striking feature of the debris is the wide range of rock types - granite (several types), marble, schist, porphyry, dolerite, quartzarenite, and basalt. This range can at present be found only between the Koettlitz and Mackay Glaciers, and the berg most probably came from the Koettlitz Glacier area.
Our sea floor sampling (see earlier) showed that present day sea floor sediment in western McMurdo sound contains less than 1% gravel, which is the dominant size fraction in the ice berg debris, indicating that ice bergs of this type are not a major sediment source.
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The texture of sea floor sediment samples and of cores obtained from DVDP 15 several kilometres north of the MSSTS 1 site suggests that wind-blown sand, in contrast to ice-rafted debris, is a major source of sediment in western McMurdo Sound. This year we carried out a small sediment sampling programme to estimate annual sediment flux from this source and to document the texture and mineralogy of the sediment.
Sampling of the sediment was concentrated in New Harbour, but several samples were also collected from near MSSTS 1. Bathymetric stations in New Harbour were used as the main sample localities with subsidiary localities further seaward and nearer the coast. Sampling was mainly by digging a snow pit (Plate XV) of uniform size (20 × 20 cm) and sediment layers within the 'block' being retained.
In New Harbour the sediments are well sorted medium quartzo-feldspathic sand and silts, and there is a marked decrease in grain size seawards. Sediments near MSSTS 1 are of basaltic composition, and generally of fine sand and silt size.
Sediments are generally blown within a mobile snow layer up to 15 cm above the sea-ice surface, although wind velocity is an important variable. The main form of movement is by saltation, debris tending to accumulate either within fresh snow dunes, or on higher relief sastrugi and old upthrust ice blocks. Sediment accumulation is more concentrated near the coast (e.g. New Harbour) and around ice bergs, (Plate XIV) which serve as effective wind-breaks. Concentrations of sediment are often found in shallow pits in the ice, sediment melting and consequent concentration on and within older, harder layers of ice.
Initial estimates on sediment flux indicate 1 × 104 tonnes of sediment was deposited by the wind on the sea ice in New Harbour in 1978, an average rate of 0.5 mm/year The sand on the sea ice is transported and deposited over large areas of the western Ross Sea when the ice breaks out and is blown north. However the accumulation rate of sediment on the sea ice can be used to infer the flux of wind-blown sediment under open water conditions, which are believed to occur for almost 1/5 of the time. On this assumption the sedimentation rate for wind-blown sand in New Harbour averages 0.1 mm/year.
References
BARRETT, P.J., TREVES, S.B. et al. 1976. Initial report of DVDP15, western McMurdo Sound, Antarctica. Dry Valley Drilling Project Bull. No. 7, Northern Illinois Univ., DeKalb, 1-100.
NORTHEY, D.J., BROWN, C., CHRISTOFFEL, D.A., WONG, K., BARRETT, P.J. 1975. A continuous seismic profiling survey of McMurdo Sound, Antarctica - 1975. Dry Valley Drilling Project Bull. No. 5, Northern Illinois Univ., DeKalb, 150-166.
Bottom sediment Paleontology of the proposed MSSTS sites in Western McMurdo Sound (David B. Waghorn and Jeffrey N. Ashby)
Bottom sediments from the proposed MSSTS Sites at New Harbour (NH) and off Butter Point (BP) were obtained by members of VUWAE 23, Event 12, using a NZOI McIntyre grab. Two 10 cm3 subsamples were taken from each grab sample, at depths of 0-1 m (1/A) and 3-5 cm (1/B) below the top of the sample.
Results
The biota includes planktonic and benthonic foraminifera, ostracods, diatoms, radiolaria, sponge spicules and small gastropods (Plate XI). No difference was observed in faunal abundance or diversity between the top and bottom subsamples at each site. Mottling and the presence of ? worm tubes in the sand indicate extensive bioturbation, resulting in homogenity of sediments and samples.
Calcareous Microfossils
A significant difference is apparent, both in species abundance and test composition, in assemblages between the two sites. At New Harbour, sample NH 1/A is dominated by arenaceous benthonic foraminifera, sponge spicules and centric (planktonic) diatoms. Common arenaceous foraminifera include Rhabdammina cf. linearis Brady, Rhizammina indivisa Brady, Reophax nodulosus Brady, Haplophragmoides rotulatum (Brady) cf. sphaeriloculus Cushman, Textularia earlandi Parker, Rzehakinidae sp, and Miliammina arenacea (Chapman). A small number of calcareous benthonic foraminiferal taxa including Trifarina earlandi Parr, Fursenkoina daviesi (Chapman & Parr), Robertina sp. and Globocassidulina crassa rossensis Kennett, occur. Also, two juvenile specimens (ostracod) Echinocytheris cf. dasyderma (Brady) have been identified. Sample NH 1/B is dominated by arenaceous taxa, but reduced in diversity compared to sample NH 1/A. Both samples lack Neogloboquadrina pachyderma (Ehrenberg).
In contrast, both Butter Point samples (BP 1/A & BP 1/B) are dominated by calcareous benthonic taxa. Species present include Trifarina earlandi Parr, Ehrenbergina glabra Heron-Allen & Earland, Astrononion antarcticum Parr, Pyrgo williamsoni (Silvestri), Globocassidulina sp. and Fursenkoina daviesi (Chapman & Parr). Most of the New Harbour arenaceous taxa also occur in abundance in the Butter Point samples. Sinstrally coiled Neogloboquadrina pachyderma (Ehrenberg) are common. Ostracod taxa present are Australicythereis polylyca (Muller), Xestoleberis sp, Krithe 2 spp, Australicythereis sp and Trachyleberis sp. cf. Cythere polytrema Brady.
Siliceous Microfossils
Very low radiolarian abundance was encountered at both sites. The New Harbour assemblage is dominated by Lithelius nautiloides Popofsky, the remaining taxa being Antarctic strelkovi Petrushevskay, Spongotrochus glacialis Popofsky and Spongodiscus cf. favus Ehrenberg. At Butter Point, Radiolaria were of even lower abundance than at New Harbour. The New Harbour assemblage is dominated by Lithelius nautiloides Popofsky, with Spongotrochus glacialis Popofsky and Antarctissa cf. denticulata (Ehrenberg) present. The diatom taxa, Coscinodiscus lentiginosus McCollum, Eucampia balustrum McCollum, C. sellaris McCollum, Charcotia irregularis Peragallow, Pseudoenotia sp and Denticula sp occur in the Butter Point sample.
Discussion
The age of young marine sediments in the shallow parts of the Ross Sea is as yet difficult to determine paleontologically. Of the seventeen Brunhes and Gauss age diagnostic taxa described by Fillon (1972) twelve are restricted to depths greater than 450 metres. The remaining five taxa occur at shallower depths. Two of these,
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Globocassidulina crassa rossensis Kennett and Cassidulina porrechis Heron-Allen & Earland, are found at New Harbour and Butter Point respectively. Both species indicate a Brunhes age (Fillon 1972, 1974). The presence at Butter Point of the diatom taxon Eucampia balustrum McCollum found in Gilbert to Brunhes sediments, but more commonly restricted to the Brunhes, also supports a Brunhes age for the Butter Point assemblage. Radiolarian species found have extended age ranges and precise age determinations cannot be made. Present day (Recent) Ross Sea taxa are typically endemic and similar to Gauss assemblages (Fillon 1973).
The difference in foraminiferal test composition between the New Harbour and Butter Point Sites, dominantly arenaceous and dominally calcareous species respectively has been described in other regions of McMurdo Sound and the Ross Sea (McKnight, 1962; Kennett, 1966; Fillon, 1972, 1974). Kennett (1966) suggested that a calcium carbonate solution boundary (CCD) occurred at 500-550 metres, separating arenaceous faunas below from calcareous faunas above. Fillon (1972) described 'relic Gauss' and Brunhes sediments which contain dominantly calcareous and arenaceous taxa respectively. He explained the latter as due to an increased undersaturation of calcium carbonate associated with a late Gauss - early Matuyama expansion of the Ross Ice Shelf.(Fillon, 1974. The four samples studied are well above the present day CCD.
Butter Point foraminiferal assemblages lack both the characteristic Brunhes taxon Globocassidulina crassa rossensis Kennett and its Gauss ancestor G. biora (Crespin). A possible intermediate form, Globocassidulina sp., which has a typical G. crassa rossensis shape but lacking the distinctive L-shaped aperture, is common.
High salinities, low temperature and possibly low photosynthetic activity related to the presence of semi-permanent sea ice cover may explain a calcium carbonate depletion of waters at New Harbour, though none of these parameters have been measured yet at the New Harbour Site. Arenaceous taxa may be better adapted than calcareous taxa to oligotrophic areas such as New Harbour where there is no current activity.
Neogloboquadina pachyderma (Ehrenberg) is absent from New Harbour, although photosynthetic planktonic diatoms are common. This suggests that photosynthetic activity is present at New Harbour, but not high enough to support higher trophic groups.
we thank Dr M.A. Harper for identifying the diatoms and Mr S.H. Eager for the ostracods. Mr P.H. Robinson reviewed the manuscript.
References
Fillon, R.H., 1972. Evidence from the Ross Sea of widespread submarine erosion. Nature Phys. Sci. vol 238, no. 81. pp 40-42. text figs. 1-2, tables 1-2.
Fillon, R.H., 1973. Radiolarian Evidence of Late Cenozoic Oceanic Paleotemperatures, Ross Sea, Antarctica. Palaeogeography, Paleoclimatology, Palaeoecology vol 14. pp 171-185.
Fillon, R.H., 1974. Late Cenozoic foraminiferal paleoecology of teh Ross Sea, Antarctica. Micropaleontology vol 20, no 2. pp 129-151, pls. 1-6.
Kennett, J.P., 1966. Foraminiferal evidence of a shallow calcium carbonate solution boundary, Ross Sea, Antarctica. Science vol 153, no. 3732. pp. 193, text figs. 1-2.
McKnight, W.R.M., 1962. The distribution of foraminifera off parts of the Antarctic coast. Bull. Amer. Pal., vol 44, no. 201. pp 65-158, pls. 9-23 text figs. 1-7, tables 1-5.
Thomas, C.W., 1968. Antarctic ocean-floor fossils: Their environments and possible significance as indicators of ice conditions. Pacific Sci., vol 22 no. 1. pp 45-51, text fig 1.
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FIG. 3. Sections traversed for paleomagnetic sampling at Mount Bastion (A) and west Beacon (B). Traverse line ⋰; campsites ΔΔ; D - dolerite; UL, ML, LL - upper, middle and lower Lashly Formation; WCM - Weller Coal Measures; AzS - Aztec Siltstone; BHO - Beacon Heights Orthoquartzite; AR - Arena Sandstone; AMF Altar Mountain Formation NMS - New Mountain Sandstone; FG - Feather Conglomerate.
Paleomagnetic sampling of Beacon and Ferrar rocks (D.A. Christoffel)
The Beacon Supergroup in the McMurdo Sound region is a flat-lying continental sequence about 2000 m thick and ranging in age from Early Devonian to Late Triassic (400 to 180 m.y. B.P.). It was extensively intruded by sheets of Ferrar Dolerite in the Early Jurassic. The ultimate objective of our programme - to determine a polar wander curve for Antarctica for this 200 m.y. period - has yet to be achieved. However the secondary aim - devising and carrying out a field programme of collecting oriented rock samples - was successfully accomplished.
The field programme was to take oriented samples at time intervals of no longer than 0.5 m.y., roughly one every 3 m. Coring is the only feasible technique, but to date coring attempts in the Antarctic had been unsatisfactory. The main problems had been the large quantities of cooling fluid needed, the inability to use water, and the weight and unreliability of the equipment.
A 22 cc TAS back-pack motor (Plate XVI) used for tree trimming and grass cutting was adapted by attaching a specially designed coring head (Plate XVII) to the flexible drive. The coolant, a glycol and water mixture, was metered by a stock drenching handpiece. The entire unit, including 5 litres of antifreeze, weighs 14 kg.
Under 'normal' operating conditions, at least 2 litres of water was used per core. The aim was to reduce this consumption to less than 1/2 litre per core. For 600 cores, approximately 150 litres of antifreeze with a 1:1 mix would be required. In the event, 30 gallons (135 litres) was taken since the motor was low powered, thin walled coring stems were obtained as they require less driving power. These would be more likely to wear than the normal heavier corers so 10 core stems were taken.
Technique of taking cores
A suitable site, with exposed weathered bedrock is selected. This often requires much clearing with a geological hammer. It is then cored to a depth of approximately 100 mm. The orientation of the sample is measured and recorded (in our case the dip and strike of the top surface). This is done by inserting in the hole a tube (Plate XVIII) with an adjustable plane table. The table is levelled and the strike measured, preferably with a sun compass, but at least with a magnetic compass. The sample is then removed, marked and bagged. Even under good conditions in temperate climes, two operators take about 10 minutes per core.
Operation in Antarctic Conditions
We quickly found that the magnetic readings of both our geological compasses were unreliable. It was thus necessary to work with the sun on the rock face. At Mt Bastion, 75% of the section was on the southern face. This required working in the very early morning when temperatures were low (−25° to −30°C). Even so, the motor performed very well, usually starting first pull. However, the 1:1 antifreeze mixture froze. It was increased to two parts antifreeze to one of water and finally 100% antifreeze, when no further trouble was experienced. The handpiece metering system worked well and on average, four cores per litre were obtained.
Mount Bastion
A major difficulty here was the weather and the snow that accumulated during our stay. The weather was normally fine in the early morning, but by mid-day, had clouded over and snow was falling. This normally continued for the rest of the day. By the end of our time, most of the slopes were covered by about 300 mm of snow. We were fortunate in having the initial two fine days with clear rock. By carrying
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out the reconnaissance with P.J. Barrett who had described the section previously (Barrett and Webb, 1973), we were able to select the locations we wished to sample in the first few days and were subsequently able to carry on almost blind, which was a distinct advantage considering we worked much of the time in near white-out conditions and our tracks from one day to the next were almost obliterated. We are very grateful to Dr Barrett for making this time available.
West Beacon
Sampling at West Beacon was much more rapid. Our camp on the northeast ridge was almost half way up the section, and a minimum of time was spent in travelling to the sites. We benefited considerably by a third person in the party. Two people orienting and collecting the samples can slmost keep up with one driller.
The weather was better and although there was some snow on the rocks near the summit, it was easily cleared.
The slopes containing the chosen section faced north and northeast, enabling sampling to be carried out during the normal day. Sun compass orientations were obtained on a large proportion of samples.
The effect of these factors is reflected in the fact that it took 7 days to sample an equivalent length of section that took 14days at Mt Bastion.
We started sampling near the bottom of the section, at the New Mountain Sandstone - Altar Mountain Formation boundary in the Devonian - the exposures below this were very scattered beneath scree and it was difficult to tell whether they were in place.
Sampling was straightforward up and through the Arena Sandstone to the very prominent Beacon Heights Orthoquartzite (BHO) boundary. The rock was rather friable near the contact with dolerite sill, presumably due to baking. Some cores were taken through the 150 m thick dolerite sill. The section was then continued further around to the North and more directly up to the main peak. The BHO - Aztec Siltstone contact was a prominent erosion surface. The Aztec siltstone was characterised by hard layers of dark green siltstone which gave good cores.
The Weller Coal Measures (Permian) comprised the topmost part of the section to the summit dolerite cap rock. It was fairly coarse and extensively cross-bedded, but had no coal beds here - very similar to the lower Weller at Mt Bastion. The sampling overlap between here and Mt Bastion should provide a useful check on the reliability of the paleomagnetic measurements.
During the coring of the last few samples, the motor was behaving erractically and had considerably reduced power. With the day remaining after finishing the Beacon Heights section, the motor was decarbonised and the spark plug checked. In addition the samples were packed for transport.
Table Mountain
In the three remaining days of our programme, we had been scheduled to join Event K12 at New Harbour. Since they had already completed their programme we instead moved to Table Mountain in order to complete our sampling of the Beacon sandstones, which, in this region rest at the Kukri Erosion Surface, which is cut in plutonic basement rocks.
On Friday 15 December, we arrived at Table Mountain. Karen Williams replaced Peter Garden, who had twisted his knee on the final sampling day at Beacon Heights and returned to Scott Base as a precautionary measure.
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The remainder of the 15th and part of the 16th were spent surveying the section. Then the motor malfunctioned and the rest of the day was used in repairing it.
Consequently, Sunday 17th, the last day began at 0100. We started at the bottom of the section, about 1 1/2 hours' walk from the camp. Although clear, it was very cold. The petrol hose froze stiff and fractured, but after being retained and restarted, the motor ran for about 15 minutes and stopped, due to no spark. We returned to camp, stripped the motor, to find a short at the contact breaker and returned to the top of the section by 1200. It had started to snow, but this time we worked down. We completed our sampling near the base of the section at 1900 hours. By this time approximately 300 mm of snow had fallen and visibility was very restricted.
Conclusions
The sampling of cores in the Beacon section was very successful. The lightweight coring equipment worked well, enabling us to collect samples more efficiently than our coring equipment used in New Zealand. The system was ideally suited to a team of three. The hand piece, used for dispensing the coolant, finished up being held together by string and wire, but modifications should overcome this problem. Significant saving in cooling fluid was achieved so that bulk and weight of equipment and samples were reduced to a minimum.
Contact Metamorphism at Mount Bastion (Chris Mroczek)
The aim of this project was to sample the contact zone and surrounding sediment, associated with a Jurassic dolerite intrusion. Detailed laboratory analysis will be carried out during the year. Mt Bastion was chosen as a suitable site for sampling, as a 170 + m sill overlies approximately 500 + m of Lashly sandstone (Triassic) The sill was thought to be thick enough to have more than just a local baking effect; also the sandstone is generally feldspathic and should therefore be more prone to mineralogical changes as a result of sill intrusion than say, a quartzose sandstone.
The dolerite sill, the chilled margin (0.6 m) the contact between the chilled margin and the underlying sediment and sediment for a distance of 200 m from the sill were sampled extensively. In the field the effect of the sill, the green colour of the sediment caused by the oxidation of chlorites in the matrix (Korsch, 1973; Haskell, 1964), was obvious for approximately 1 m only.
| i) | The mineralogy of the contact zone to see if any new minerals have been formed as a result of the intrusion, and the reactions leading to the formation of these minerals. |
| ii) | For what distance the underlying sediment has been affected, to try and distinguish between sill effects and diagenetic effects. |
| iii) | The original temperature of the contact zone. Stability limits of minerals such as chlorite have already been used to determine temperature ranges. Haskell (1964) used the chlorites brunsvigite and ripidolite obtained a minimum temperature of 350°C and a maximum of 700°C. Barrett (1966) used colour loss in pink zircons to determine an upper limit of the temperature reached in the sediments (around 450°C) |
High pressure, high temperature work will hopefully be carried out to try and simulate original conditions. No detailed work of this kind has been carried out before; only general observations by various workers have been produced previously.
References
Barrett, P.J., 1966. Petrology of some Beacon Rocks between the Axel Heiberg and Shackleton Glaciers, Queen Maud Range, Antarctica. Jour. of Sed. Pet.
Haskell, T.R., 1964. Thermal metamorphism of Beacon Group Sandstone of the Taylor Valley, Antarctica. Nature vol 201.
Korsch, P.J., 1973. Petrographic comparison of the Taylor and Victoria Groups in South Victoria Land, Antarctica. N.Z. Jour. of Geol. & Geophys. 17.
Permian coal measures at Mount Bastion and Mount Fleming (Alex Pyne)
At Mt Bastion sedimentary strata of the Victoria group (Beacon Supergroup) and the intruding dolerite were mapped to aid the paleomagnetic and metamorphism studies. In the area mapped the strata is generally flat-lying and intruded by terminating and climbing sills, although in the area at the head of Gibson Spur immediately to the south the dip of the Beacon strata approaches the vertical.
Two detailed sections were measured from the Weller Coal Measures, here 200 m thick into the Feather Conglomerate. A point of considerable interest is the discovery of fossil soils (Plate XX) preserved in a sequence of silty beds forming the gradational contact between the Weller Coal Measures and overlying Feather Conglomerate. Soil horizons are extremely rare in any of the Permian coal measures of the Southern Hemisphere. Similar horizons were found in the same stratigraphic position at Mt Fleming.
The Beacon Supergroup and the intruding Ferrar Dolerite were also mapped at Mt Fleming (Plate XXIII) and Horseshoe Mt., and three laterally related sections of the Weller Coal Measures were measured in detail. The Beacon strata at Mt Fleming extend from the upper Beacon Heights Orthoquartzite (Late Devonian) to the Lashly Formation (Late Triassic). They are in part monoclinally folded and probably faulted also, in contrast to most other areas in south Victoria Land where there is scarcely a hint of tectonism. Careful mapping showed that the vertical displacement (throw) across the faulted monocline was about 230 m. The detailed study of the Weller Coal Measures begun this season will be used to determine a depositional model for the coal measures. Initial work this year has shown that in the lower and upper parts alternating coarse feldspathic sandstone and shale-coal horizons have resulted from channel and overbank deposition (Plate XXII) The middle part, predominantly medium to fine sandstone, is of channel deposits containing silicified-calcified logs and stumps in growth position (Plate XXI). This indicates exposure of channel bars for periods of time up to two hundred years.
Seismic, Audio, and Magnetic readings at Erebus Volcano, December 1978 (Ray Dibble)
Volcanic earthquakes and eruptions from Erebus volcano (Plate XXVI) were detected by a geophone at Camp Cave, a low frequency microphone at the main crater rim, and a magnetic induction loop around the crater rim, and recorded on tape between 14 and 25 December 1978. Small earthquakes were as numerous as in December 1974, but larger ones (<1 kJ, including explosion earthquakes) were less frequent (Fig. 4). There was a weak and doubtful peak at 12-14 hours NZST in the occurrence of large earthquakes during the day, but not in the occurrence of small earthquakes (Fig. 5). Of well recorded earthquakes exceeding 10 J, 24% also appeared on the microphone channel, 5% on the magnetic channel, and 10% were accompanied by observed eruptions. The microphone events (which had dominant frequency 1-4 Hz) were of four distinct types: One corresponded with explosions of the Active Vent (Plate XXVIIA) but not with magnetic signals, and two other types (Plate XXVIIB & C, with rare-factional audio onsets) often corresponded with magnetic signals, but the fourth and most common type (Plate XXVIID), for which the air-wave velocity is confirmed, corresponded only with a particular type of earthquake with simple onset. Earthquakes accompanying the other audio types had fore-running vibrations beginning up to 45 s earlier. Lava bulged from the Active Vent during the forerunner before the explosion which occurred while W.F. Giggenbach was in the inner crater, but no signals corresponded with the 2-5 m drop and rise of Lava Lake level in the 15 minutes after the explosion. Occasional brief periods of volcanic tremor were recorded for the first time in December 1978.
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FIG. 4. Number of earthquakes of all types at Erebus volcano per day (in 5 dB ranges) versus seismic energy, for 1974 and 1978. The number of small earthquakes and slope (b) of the curve were similar in 1974 and 1978. The excess number of larger earthquakes (mostly observed explosions) was less in 1978 than 1974.
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FIG. 5. Average number of earthquakes each 2 hours of the day (NZST) at Erebus between the dates shown.
Left: Earthquakes (mostly explosions) with seismic energy 10 kJ show a possible peak at 12-14 hours.
Right: Earthquakes (mostly B-type) - 0.1 = 10 kJ show no consistent peak.