PART I - McMURDO SOUND SEDIMENT AND TECTONIC STUDIES (MSSTS)
Coring began: 21 October, 1979
Coring ended: 22 November, 1979
Position: 77° 33′ 25.83″ S; 164°23′ 12.85″
Water depth: 196 metres
Drilled depth baton, sea floor: 229.6 m
Number of cores: 73
Percentage core recovered: 44%
- Depth below sea floor: 229.6 metres
- Lithology: Stratified, muddy, very fine sand with rare small pebbles
- Age: Middle Miocene
Two of the outstanding problems in Antarctic earth science are the early history of the East Antarctic Ice Sheet and the history of the Transantarctic Mountains, and they may well be linked. The GLOMAR CHALLENGER made the first major breakthrough in 1973 by recovering cores from the centre of the Rose Sea showing that ice rafting began there 25 m.y. ago and has been going on ever since (Hayes et al., 1975), but whether the floating ice came from East or West Antarctica is still debated. The cores contained little information about the history of the Transantarctic Mountains because the holes were too far offshore, and there is unlikely to be much further information from on land, for no dateable sequences from the key time period (50-10 m.y.) are known to crop out on land in the McMurdo Sound region. The glacial history and the uplift of the mountains are likely to be best recorded in the thick sedimentary sequence seen in seismic profiles along the Transantarctic Mountain Front (Northey et al., 1975). This sequence can be sampled only by drilling.
The first attempt to core this sequence (DVDP15) reached 65 m sub-bottom before sea ice conditions terminated drilling (Barrett et al., 1976). The second attempt, which is described here, was much more successful, though drilling was again terminated by sea ice conditions before the target depth was reached. Further background to the drilling can be found in Barrett (1979) and in the Scientific Operations Handbook (Barrett s Waghorn, 1979). Personnel for the operation are listed in Table 1.
Location of Site and Setting up Camp (BAS)
Field operation of the MSSTS programme began with the arrival of an advance party of ten, including one from VUW, at Scott Base on 28 August 1979. Vehicles and equipment were prepared and a series of reconnaissances undertaken by Power wagon and Snotrac (Fig. 2). A flagged route closely following the southern and western boundaries of McMurdo Sound was established from Scott Base to New Harbour. Rough ice prevented an initial attempt to establish a route directly out to the MSSTS 1 site from the dump of DVDP drilling gear at Rig Point on the northern shore of New Harbour. During a Subsequent reconnaissance good travel was found on a route bearing 030 true from Butter Point.page 5
On September 19 a reconnaissance party arrived at a point at 77. 33.3S:164 23.4E. The locality of the site was reached by dead reckoning and the position on the sea ice was fixed by resection using a Kern DkM 1 theodolite. Although 3 km SW of the proposed site (Barrett, 1979) the site was logistically preferable, being nearer land, and scientifically acceptable, being within the region previously surveyed by seismic refraction methods (McGinnis 1979) and known to have at least 500 m of sediment overlying basement.
Sea ice thickness at the adopted site, 1.98 m, was more than sufficient for drilling operations; water depth was 196 m and not varying from this by more than ±10 m at points 50C m north, south, east and west. The site was 80 km by sea ice road from Scott Base and 26 km from Rig Point.
Two huts were established at the site and an attempt was made to flood the area with sea water to strengthen the sea ice platform. The attempt failed as the pumps froze - the air temperature was −35° C. In the following weeks equipment and fuel were brought to the site by D4 sledge trains from Scott Base, McMurdo Station and Rig Point. By October 10 the camp, consisting of two oil-heated Jamesways and six insulated plywood huts, was fully operational and most of the drilling gear was on site. The main party of drillers arrived on October 12 and the erection of the rig began immediately. Casing was lowered to the sea floor on October 20 and drilling began on October 21.
Figure 2. Map of McMurdo Sound, showing the location of MSSTS 1 and DVDP 15 and supply routes to MSSTS 1.
|Drilling supervisor||Jack Barclay||MOWD|
|Drilling Supervisor||Jim Gupwell||MOWD|
|Driller||David Rees||Ant. Div.|
|Drillers assistant||Tony McPherson||VUW|
|Drillers assistant||Paul White||VUW|
|Drillers assistant||Frank Williams||VUW|
|Logistics Manager||Garth Varcoe||Ant. Div.|
|Cook||Warwick Bull||Ant. Div.|
|Ass. Maintenance Officer||Ray Matheson||Ant. Div.|
|Field assistant||Roy Arbon||Ant. Div.|
|Science Manager||Bryan Sissons||VUW|
|Core grabber||Alex pyne||VUW|
|Core grabber||Ian Wright||VUW|
|Geophysicist||Dr Heinz Miller||FGR|
|Core Lab. Scott Base|
|Site Geologist||MSSTS Pt 1 Dr Peter Barrett||VUW|
|Site Geologist||MSSTS Pt 2 Dr Barry McKelvey||UNE|
|Core Manager||David waghorn||VUW|
|Geological Asst.||Barry walker||VUW|
|Geochemist||Dr Tetsuya Torii||JARE|
|Geochemist||Dr Kazuhisa Komura||JARE|
|Geochemist||Dr Shyu Nakaya||JARE|
|Geologist||Dr Yuki Yusa||JARE|
|Geologist||Dr Don Elston||USGS|
|VUW||Victoria University of Wellington|
|NIU||Northern Illinois University|
|USGS||United States Geological Survey|
|UNE||University of New England|
|FRG||Federal Republic of Germany|
|JARE||Japanese Antarctic Research Expedition|
|MOWD||Ministry of Works and Development|
|Ant. Div.||Antarctic Division DSIR, N.Z.|
Onsite handling and description of core (ARP)
The procedure for extracting core from the core tube varied depending on the core size being drilled. HQ core (dia. ≈ 63 mm) was recovered in a split tube ("splits") within the core tube. The 10 foot long splits containing core were hydraulically extracted from the tube and transferred intact and unfrozen onto the specially constructed bench in the Science Hut. The smaller sized NQ & BQ core tubes did not have splits. Core therefore was directly removed from the tube onto an HQ 'split' by gently tapping the tube and extruding the core with a steel rod. Often the tube had to be heated in a "Herman Nelson" hot air hose to unfreeze water surrounding the core before extraction could proceed. NQ & BQ cores therefore suffered some sub-horizontal fracturing resulting from core extraction. These fractures, however, were fresh and easily distinguished from natural fracturing within the core. Boxing, initial examination and description was done on the unfrozen core in the Science Hut.
The primary purpose of the onsite description was to record as accurately as possible the depth from which core was recovered and any features which might be changed by freezing and transportation to the core lab.
Information from the driller often enabled a more accurate determination of from where core was recovered during the coring run. This was particularly important when recovery was less than 100%. The position of core recovery was shown at the graphic log, a double line being used to indicate the bottom depth of the run when the run was not the full 10 feet. When doubt existed about the exact depth of "the core, it was assumed to have come from the top of the run.
Fracturing was noted on the graphic log and where possible determined as natural or induced from drilling and core extraction. Some mudstone lithologies initially recored and intact cylindrical blocks suffered extensive conchoidal fractures on subsequent freezing.
The colour of the core was compared with the "Revised Standard Soil Colour Charts" (Japan). Bioturbation and bedding was often most easily seen when the core was fresh and wet.
Seismic (Sonic) Velocities (PCF)
Routine on-site measurements of sonic velocity, density and chemistry of the core were planned. Due to low and fluctuating temperatures in the Science Hut and the cramped space, only sonic velocities were finally performed. Sonic velocity measurements were undertaken with a PUNDIT, determining the travel time between two transducers of an 82 kHz pulse, as described in Barrett & Froggatt (1978). Only whole, coherent segments of core free from fractures or clasts and at least 50 mm long were chosen. Sampling between transducers and core was improved by washing measuring points on the core with water and use of water as a complant. Grease or oil was avoided to lessen core contamination. Consistent readings about the core axis were obtained in this manner. Measuring was performed as soon as possible after cote recovery, usually as soon as the core was boxed and before initial logging. Except for Core 2, the cores remained unfrozen. Time after recovery was usually less than one hour although delays of up to eight hours occurred.
Velocities measured ranged between 1.78 and 5.10 km.s−1 for sediments and 3.44 to 5.92 km.s−1 for basement clasts of dolerite, granite etc. Clast velocities agree well with the data of Barrett & Froggatt 11978). However, sediment velocities were generally higher than determined from seismic refraction profiles in McMurdo Sound (Barrett 1979, Nor they et al., 1975) and more varied than for DVDP 15 where many of the cores were frozen (Barrett s Treves, 1976). Velocities determined on each core or unit within a core have, initially been averaged (Table 2) and plotted against depth (Figure 3). A steep uniform velocity gradient of V = 19.OH + 1.6 (V = velocity in kms and H = depth in km) is shown to 110 m sub-bottom where there is a marked velocity reversal. A further reversal occurs at 190 m. Reflectors labelled A, K, B & C (Northey et al., 1975) have been tentatively identified at 141 m, 168 m, 180 m and 210 m sub-bottom respectively. The lithology of each reflector is a well page 8 cemented medium sandstone up to 0.5m thick with velocities of between 4 to 5 km.s−1, compared to 2.0 - 3.5 km.s−1 for less cemented material adjacent to the reflectors. There is no apparent correlation between these reflectors and lithologic units. There is an overall good correlation, however, between lithology and reversals in the overall velocity gradient.
Sonic velocities determined with the PUNDIT were found to provide quick, easy and reliable measurements on the core. These allowed the actual Velocity profile to be built up as drilling proceeded with consequent readjustment of projected target depths using the available seismic reflection records. Only reflectors A, C, & D were recognised on the reflection profiles beneath MSSTS 1, so once A had been penetrated, adjusted velocities gave projected depths of C at 204 m and D at 270 m sub-bottom. Based on two-way travel times from Track XXII (Northey et al., 1975) depth estimates were revised after each reflector was recognised. Calculated and actual depths are compared in Table 3. General close agreements between depths indicates reliability of average core velocities.page 9 page 10 page 11
Gas Composition (KK)
The gas composition dissolved in circulating water from drill hole has been analyzed by using a gaschromatograph (Shimadzu GC-30AT) coupled with a pen recorder. The amounts of O2, N2 and CH4 are measured by a Molecular Shieve 5A column, and those of air Components (O2 + N2). CO2, CH4 and C2H6 by a Porapac-Q column.
The equipment was set in a small hut placed just near the drill-rig. The gas analysis was made at constant column temperature (15°C). Helium was used as carrier gas.
The time table of working at drill site is:
Nov. 1-2 Set-up of equipments at drill site
Nov. 8-17 and 20-23 Analyses of gas composition of water and ice samples.
Because the drilling condition was not good at the time of Nov. 8-23, only five measurements were made for circulating water from the bottom of drill hole. Gas composition of room air, atmospheric air, and dissolved gas in sea water were also measured for comparison.
Preliminary results are summarized in Table 5. As seen from the table, CH4 and C2H6 were not found in circulating water samples. Low oxygen contest (6–15%) and rather high CO2 content (1–6%) are commonly observed for water samples except for sample no.5, the gas composition of which is the same as that of sea water. However, main components (O2 and N2) are not much different from the atmospheric air. This fact suggests that the dissolved gas in the circulating water is mainly from atmospheric air, probably sucked in by the pump used for water circulation. The low oxygen content may have caused by contact of sucked air with the down hole sediment, which is in a highly reducing state.page 12
|Sample No.||Date of Sampling||Downhole Depth (a)||O2||N2||CO2||CH4||C2H6|
|1||Nov. 12||179||11.6||83.0||0.4||Not detected||Not detected|
|2||Nov. 15||183||9.||85.4||5.6||Not detected||Not detected|
|3||Nov. 15||186||6.1||92.8||1.1||Not detected||Not detected|
|4*||Nov. 15||186||14.6||85.4||1.0||Not detected||Not detected|
|5||Nov. 15||202||31.1||68.9||Not measured||Not detected||Not measured|
|6||Nov. 21||sea water||30.1||68.8||1.1||Not detected||Not detected|
|7||Nov. 21||atmospheric air||21.2||78.8||0.04||Not detected||Not detected|
|8||Nov. 21||room air||18.0||81.7||0.31||Not detected||Not detected|
|9||Nov. 8||sea ice||(0.26 ml air/sr.-ice)|
Surveillance of the Sea Ice (BAS)
Four bench marks number BM1 to BM4 were established on a line bearing 300° and situated at 25, 50, 100 and 200 metres respectively from the rig (Fig. 3). These, together with a point on the Science Hut 10 m from the rig and a point on the rig itself were levelled throughout the drilling operation. Until October 19 a Kern DkM1 theodolite was used, thereafter a Wild level; observational error is estimated at less than ±5 mm. Differential vertical movements of all stations relative to BM3 are plotted in Figure 4 which shows that BM1 and BM2 descended rapidly with respect to BM3 in the period October 10 to 19 when weight was being concentrated at the rig. There followed a 10 day period during which a small but significant rebound occurred. This was greatest and most pronounced at BM2, the farthest station from the rig measured other than the datum bench mark BM3. After October 28 BM1 & 2 and the Rig show a consistant subsidence relative to BM3 while BM4 had risen, Which is taken to indicate that BM3 in fact descended relative to sea level and that the zone of subsidence due to loading at the rig exceeded 200 m in diameter. The total subsidence of the rig relative to BM4 in the period October 28 to November 21 was 65 mm.
Late in the drilling operation when snow had ablated from the sea ice surface a number of old healed cracks were discovered in a region 40 m from the rig. In contrast to the experience at DVDP 15 no relative movement was observed on any existing cracks and no new cracks in the vicinity of the rig or camp were observed during the entire operation.
As at DVDP 15 differential slackness on the guy ropes of the drill mast occurred. The slack guys were on the side of the mast loaded by the main lifting pulley. The amount of slackness increased with load and was attributed to deformation of the mast.
Ice thickness was monitored and is graphed in Figure 4. On September 19 when the site was first visited the ice was 1.98 m thick. The ice thickness increased to 2.33 m by November 14 after which there was a slight decline to 2.28 m at the termination of drilling. All thicknesses were measured in a small region about 10 m from the rig. During the bathymetric survey of the drillsite, ice thickness was measured in 16 holes and found to be the same to within 20 mm over the entire area.page 13
On October 8 during a 30 hour break in drilling, downhole temperatures were measured using a thermistor and bridge circuit on loan from the Physics Department, VUW.
Seven temperature readings at known vertical spacing were obtained in the hole plus two further readings in the water column above.
The thermistor was calibrated prior to the field season with cable and bridge held at room temperature (about 15°C] and only the thermistor temperature lowered. Using this calibration a temperature of −3.3°C was obtained for the seawater above the hole. As it is known that the water temperature in McMurdo Sound is remarkably constant at −1.8°C it appears that either the instrument had drifted since calibration or the bridge circuit was affected by low ambient temperatures. A re-calibration was made on site using Mercury thermometers and a commercial thermistor temperature probe. The new calibration curve was approximately parallel to the old but gave a temperature for seawater closer to the expected value of −1.8°C.
Downhole temperatures derived from both calibrations are plotted against depth in Fig. 5. Absolute values of temperature are known to be in error but the estimate of temperature gradient is not thought to be badly affected. The gradient, 35°C/km, is slightly higher than the value of 31°C/km obtained at DVDP 15.
Tidal Measurements (BAS)
A tide gauge consisting of a line anchored to the sea floor and running over a pulley suspended above the sea ice (Fig. 6) was set up in the Science Hut adjacent to the rig. Tidal movements were recorded by taking off the movement through a pulley reduction system onto a chart recorder. Usable records were obtained for the periods 1 to 25 September inclusive and 1 to 24 November inclusive. Until 9 September a reduction of 13.6:1 was used, thereafter 10.1:1. The maximum tidal amplitude was 0.89 m. In addition to the main tidal variations with periods of about 24.20 and 12.20 hrs small cyclical movements with amplitudes of a few mm and periods of 5–50 sec occurred. These are attributed to attenuated ocean swell and were too small to be measured by the recorder.
Bathymetric Survey of the Site (BAS)
Water depths were measured by weighted metre line on a, 200 metre grid surrounding the site. Results are summarized in Figure 7. The sea floor around the site has a very subdued topography with an approximately north-south strike and gentle dip to the east.page 16
VUWAE "Drillers" (A. McP)
Three student members of VUWAE 24 worked as offsiders on the Longyear 44 drill rig alongside MOW drillers during the MSSTS project. Shift work began on October 16 in 8 hour shifts with one VUWAE member in each of three of the four drill crews. Some of the jobs done by the student offsiders are described below. The rig set up is shown in Figure 8.
Two ten foot lengths of drill pipe were joined to make 20 foot "stands". This was accomplished by means of chain vices and stilsens.
Floor work in the drill shack included joining and breaking of "stands" to and from the drill string, monitoring pump pressure, and general maintenance.
Derrick work consisted of detaching the winch howser from the "stands" while "tripping out" (removal of the entire drill string from the hole), and attaching it while "tripping in". This was often very uncomfortable as the derrick was exposed to all weathers.
Core pulling, or "grabbing" included breaking the drill string and lowering a light wire line with an "overshot" attachment down the hole. The "overshot" latches onto the core barrel, which is then pulled up the hole by winch. The core was then removed from the barrel by a high pressure water jet or other means.
Mixing of mud was always enjoyable, though often rather more grubby. This consisted of mixing the various drill muds and gels in the mud tanks with the help of motorized stirrers. The mud was then pumped down inside the drill string, returning up the casing and bringing with it rock clips from the drilling.
We also acted as general "dogs body", which included any tiling from getting the coffee (and not forgetting the biscuits) for smoko, to refuelling the rig and pump at the end of the shift.
The VUWAE members also assisted in the packing up of the camp and dismantling of the rig. All rig gear and camp buildings were dismantled and towed on sleds by D4 caterpillar back to Scott Base. Because this was such a long (9 hours), slow, monotonous and potentially dangerous trip, the D4 was escorted by a student in a Snotrac. "Riding shotgun" was at times a rather tedious task but enjoyed by most as it gave an opportunity to be relatively alone and reflect on the Antarctic surroundings.page 18
CURATIOS AND ANALYSIS OF CORE
Transport of Core (DBW)
Forty-one boxes of core were transported from the drillsite to Scott Base by U.S. Navy Helicopters, Power Wagon and octago sledge pulled behind by a D4 crawler tractor.
Although some core damage has occurred, mainly in the larger size HQ and NQ cores, this is attributed to drying out of the core, rather than damage due to transport. No difference in core preservation was observed between the different modes of transport.
The first 2 1/2 metres of core recovered, considered to be from a frozen layer deteriorated rapidly. No deterioration in the consolidated material occurred.
Storage and processing at Scott Base:
|(1)||Wooden blocks labelled with corresponding sub-bottom depths and core number were placed in the core box;|
|(2)||Smear slide samples were taken and the detailed core description completed;|
|(3)||Each core box was photographed in colour and black and white;|
|(4)||Core was then sampled and stored (in an unfrozen state).|
Transport to New Zealand:
Core boxes were packed into a wooden cargon which was consigned from Scott Base about the 5th of December.
It was despatched from Christchurch on the 7th December, by rail to Wellington where it arrived on the 21st December. The cargon was picked up by carrier and arrived at the Geology Department on 28th January.
Little physical damage to the core occurred during transport back to New Zealand although a fair amount of relative movement of core pieces occurred within individual boxes.
A preliminary investigation by Dr Ann Bell (Botany Department, VUW] showed the presence of Hyphomycete fungi in four of the forty-four boxes, growing on core labels (gummed paper) wooden blocks and in some cases on the core.
Fungi growing on the core labels was either Penicillium sp or Paecilomyces while an Actinomycete, possible a Streptomyces sp, with very fine hyphae and chains of cauidia was growing on the core. Neither organisms could be mistaken for pollen grains.
Core Photography (AHR)
Duplicate photographs of boxed core were made with both FP4 black and white film and Ektachrome 200 colour slide film. The core was photographed following the insertion of wooden blacks showing core number and sub-bottom depth and where possible prior to both core description and sampling.
Two 35 mm cameras with 50 mm lenses, mounted 1.1 metres above the core on adapted tripods were used. A Sunpack model 411 electronic flash was used for lighting with a double layer of tissue taped to the front to diffuse the light. A centimetre scale, Kodak colour separation guide and grey scale were used and are visible in each photograph.page 20
The black and white film was processed at Scott Base and printed on 10 × 8 Ilfospeed grade 3 paper. These photographs were found to be extremely useful for both locating sample positions and for general use.
Colour film was processed in New Zealand.
Core Sampling (DBW)
535 samples for ten investigators were collected from the core during the drilling period (Table 6). Each sample is recorded in a sample register and the position labelled with the investigators initials in the core box. This should enable sample localities to be accurately located even if some disturbance of core occurs during transport or handling.
Samples have been defined by core and sections numbers respectively and measured in centimetres from the top of each section. Sub-bottom depths for each sample are calculated by adding this distance in centimetres to the sub-bottom depth of the section top.
Core Description (PJB, BC McK)
The detailed cote description was carried out at Scott Base, and the summary logs on a scale of 1:50 are being prepared along with photographs of the boxed core, for publication in the VUW Antarctic Data Series. A log of the hole with the main lithologies is given in Figure 9.
Although a procedure for description was outlined in the Scientific Operations Handbook, pressure of time, facilities and differences in background of the four people involved lead to some unevenness in the descriptions. This problem is being overcome by reference to the core to check the summary logs. However, it is now clear that it would have been more satisfactory to carry Out a small full description at the drill site.
The strata cored at MSSTS 1 represent a moderately varied sequence of diamictite, muddy sandstone, sandy mudstone and well-sorted sandstone in units from a few to about 30 m thick. Pebbles and a few cobbles are scattered throughout, floating in the mud and sand and indicating a continuous glacial influence in sedimentation. Preliminary paleontological data [HTB; SML, BLW in this report] indicate that the sequence is entirely marine and. from 32 m to the oldest core, is mid-Miocene in age. The younger strata are Pliocene to decent in age. The MSSTS 1 core contrasts with the Late Miocene-Recent cores from nearby DVDP 10 and 11, in lower Taylor Valley, in that it is wholely marine, the amount and size of coarse debris is less and there is much less textural diversity.
Three main lithologies are recognised in the core recovered; diamictite, muddy sandstone or sandy mudstone, and sandstone. The diamictite is characteristically a non-stratified, very poorly sorted muddy sandstone with evenly scattered pebbles and cobbles forming 1 or 2 percent of the rock. However, all diamictite units include some intervals of stratification. The muddy sandstone and sandy mudstone units also have scattered pebbles, but are better sorted and lack the granule and coarse sand components of the diamictite, and are widely, if faintly, stratified. An indistinct mottling, attributed to bioturbation, is also common. The third lithology is the non-stratified homogeneous well sorted medium grained quartzose sand that forms unit 12. It is far more mineralogically and texturally mature than any other sediment encountered, the size and roundness of the groups indicating direct derivation from the Devonian quartzose sandstones 50 km inland.
- Wavy bedding. Stratification is slightly undulose with an amplitude of only a few centimetres, and occurs almost wherever stratification can be discerned. It is thought to have formed at or soon after sedimentation.
- Inclined bedding. This was mainly confined to the interval from 145 to 1B6 metres. Inclinations of 20 to 40° are common, though at 157 and 182 m stratification is vertical. No overturning was recognised.
- In situ brecciation of at least partly lithified strata, usually accompanied sand injection. This is common between 148 and 156 m, and was also seen elsewhere (e.g. 126 m).
The upper 12 m of the hole are unconsolidated sediment, but below this the resistance to the bit increased dramatically and the subsequent core from level to the bottom of the hole, showed a high degree of lithification, reflected in the sonic velocities of 2 to 3 km.s−1, which record an irregular increase down the hole (Table 2). Highly cemented layers of the order of a metre thick occur at a number of levels below 140 m, and several are correlated with seismic reflectors (Table 3, Fig. 9).
- The texture of the Miocene core from MSSTS 1 suggests moderately rapid sedimentation from debris laden melting ice below wave base. The diamictites were probably deposited when the glacier front was closer and soma intervals may have resulted from grounding of the ice, but there is no clear evidence of this.
- Extensive and complex soft sediment deformation within Units 9 and 10 may have resulted from shearing by ice, or slumping due to depositional instability. For Unit 10 the alternation of inclined and horizontal layers with no indication of ice contact suggests the latter.
- Composition of the core suggests it was derived from the Transantarctic Mountains to the west, mainly from the Devonian quartz sandstones of the Beacon Supergroup below 142 m, in contrast to a significantly higher basement component above that level.
- The degree of lithification suggests that the sequence below 12 m has been buried at least a kilometre at some stage in its history.
Smear Slide Analysis (BW)
The core was sampled for smear slide analysis at varying intervals depending on lithology.
Cadex was used as a mounting media and after initial problems in its application, proved to be a reasonable substitute for Canada Balsum. The slightly higher refractive index of cadex did not allow differentiation between Ca and Na plagioclase feldspar.
The smear slide analysis proved useful in determining sediment texture (sand: silt: clay ratio), mineralogy of the sand size fraction and nature of the biogenic component.
|(1)||Clinopyroxene-glass zone, from 9 to 13 metres sub-bottom, derived from McMurdo Volcanics, which are mainly less than 5 million years old|
|(2)||Biotite-hornblende Zone, from 19 metres (s.b.) to base, derived from reworked basement heavy minerals|
|(3)||Rounded quartz grain Zone, from 140 metres (s.b.) to base, containing reworked quartz grains from the Beacon Supergroup.|
Micritized carbonate (micarb) often occurs in large quanities, probably derived from the dissolution of foraminifera and other calcareous fossils or from erosion of marble basement rocks in southern Victoria Land. No calcareous nannoplankton were observed in the smear slides. Micarb appeared at 40 metres (s.b.) and occurred consistently to the bottom of the hole.
Coarse-grained, well rounded quartz, with occasional silica overgrowth, characteristic of Beacon Sandstone sediments were found in significant proportions at 130 metres (s.b.).
The smear slide analysis has proved to be useful for a quick and effective determination of mineralogical changes that occurred in the core. It is useful for determining the presence of diatoms and was the basis for detailed sampling for diatoms.
The exclusion of the coarse fraction during slide preparation caused a textural bias which resulted in an apparent increase in the amount of mud-size sediment.
Report on Foraminifera from MSSTS 1 (RML, BLW)
We sampled 72 intervals from the MSSTS 1 drill core taken in western McMurdo Sound. Core recovery was 100.15 m, 43.6% of the drilled succession. Our average sample frequency of recovered sediment is 1.4 m. The size of the samples was generally small and became progressively smaller down hole as narrower diameter core barrel was utilized. Sample sizes range from 15cc to 30cc.
Most of the samples proved to be semi-lithified diamictons. To extract the Foraminifera, we originally used the procedure of soaking and boiling each Sample in hydrogen peroxide to disaggregate the sediment. As this proved to be insufficient for most of the samples, we attempted to improve break-down of the material by drying the fragments in an oven at 120°C for three hours, then placing them in kerosene to soak overnight. Following this, the samples were removed from the kerosene and boiled in water. This procedure was applied to seven of the samples known to contain Foraminifera. This also proved to be inadequate. A second chemical, dimethyl sulfoxide (DMSO), was used on one sample, 36-5, 17-19cm, on an experimental basis to determine if it would penetrate the sediment and thus facilitate disaggregation. The sediment was boiled in DMSO at 100°C for several hours. This method also did not substantially increase disaggregation of the sediment, and as the chemical is very caustic, we returned to the use of hydrogen peroxide. This time, we preceeded the boiling treatment by crushing the larger fragments of the core samples with a hammer or mortar and pestle. The crushing was first page 24 tried on Sample 36-5, 17-19 cm, to determine the effects on the Foraminifera and other fossil material known to be present in the sediment. It had little or no detrimental effect, so we adopted this technique for all the compacted samples. Table 6 lists the samples and treatment each received.
Further processing included washing, sieving through a 63 micron standard mesh to remove clay-sized particles, followed by floatation in carbon tetrachloride to concentrate the biogenic material. Microscopic examination was then made of the floated portion. Table 7 lists the samples, the contained biogenic material, and the sub-bottom depths from which each sample was taken.
There are two foraminiferal assemblages evident in the samples we collected from the MSSTS 1 drill core. The upper fauna was found in cores 2, 10, 11, 15 and 16. It consists of twelve species, as follows: Trochammina sp., Pyrgo sp., one other species from the Miliolidae family, Fissurina sp., Rosalina globularis, Epistominella exigua, Spirillina sp., Globocassidulina subglobosa, Globocassidulina crassa, Nonion sp. (possibly Elphidium sp.), and a planktonic from the Globigerinidae family (see Table 6). The sub-bottom depths from which this fauna was extracted range from 9.72m to 32.15m. The assemblage consists of several species which are long-ranging in time, making it very difficult to determine an age for the sediments of this upper sequence.
This fauna exhibits some similarities to Pleistocene faunas from the DVDP holes 10 and 11 in Taylor Valley and also to that of the elevated marine deposits of the Cape Barne-Royds area of Ross Island (Wrenn, 1977, Ward, 1979). Rosalina globularis, Epistominella exigua (?vitrea), Globocassidulina crassa and G. subglobosa are found in all three of these sites. Species of Pyrgo, Trochammina, Fissurina, and Trifarina are also found at all three locations, though all those present in MSSTS 1 drill core have not been specifically identified to the species level. None of these taxa are particularly definitive as to time range, but the comparisons of the MSSTS 1 material with the known Pleistocene collections seen to indicate a similar age for the upper fauna of MSSTS 1.
The lower foraminiferal assemblage is also characterized by sparse faunal occurrences. The largest populations are confined to the interval from 118m to 127m sub-bottom (Cores 36 through 39), although scattered tests are found between 63m (Core 29) and 186m (Core 59). The interval from 186m to the bottom of MSSTS 1 (229m) appears to be barren of Foraminifera. Fifteen species are recognized in this lower assemblage: ?Verneuilina sp., Fissurina cf. annectens, Cassidulinoides parkerianus, C. ?porrectus, Epistominella exigua, Rosalina globularis, Elphidium Sp., Trochoelphidiella sp., Cribrononion cf. magellanicum, Globigerina quinqueloba, ?Candeina sp., Eponides tumidulus, Ehrenbergina sp., Nonionella bradii, and Anomalinoides sp. Two of these species are also present in the upper assemblage.
The small size of the lower foraminiferal assemblage and its sparse occurrences put some constraints on age determination. This fauna has strong similarities to the early and mid-Miocene assemblages from DSDP Sites 270, 272 and 273 in the Ross Sea (Leckie, Koch, D'Agostino, these in progress). The planktonic foraminiferid Globigerina quinqueloba has a New Zealand range of Otaian (early Miocene) to Recent (Jenkins, 1971). A potentially useful bioseries in the genus Trochoelphidiella Webb has been recognized in the early Miocene sequence of DSDP Stie 270 (Leckie, in progress). Continued investigations of Trochoelphidiella sp. from MSSTS 1 using the scanning electron microscope may permit better age resolution and correlation.
The preservation of the Foraminifera from MSSTS 1 is generally moderate to good. The tests have a characteristic yellowish color, differing from the clean white forms found on the floor of McMurdo Sound today. The presence of fragmented diatoms, sponge spicules, and other macrofossil debris as well as stratification of the sediments, suggests some reworking. There is no clear evidence for mixing of foraminiferal faunas of different ages. This observation, along with the quality of preservation, argues against extensive recycling of sediments. The very low abundance of Foraminifera may, in part, be explained by the small sample sizes. Oceanographic conditions page 25 influenced by the glacial regime prevalent at the time of deposition on an unstable sea floor may also be important factors inhibiting benthic productivity.page 26
Report on diatoms from MSSTS 1 (HTB)
Two hundred and thirty samples (approx. 5 cc) were taken from the MSSTS core at Scott Base for fossil diatom analysis. These were treated with Hydrogen Peroxide in the U.S. Thiel Earth Laboratory at McMurdo and smear slides were made using Naphrax as a mounting media.
Fossil diatom fragments occur in at least 60% of the samples. Preservation is poor and identification difficult. No samples have been found which can provide an easy key to the stratigraphy such as occurred in DVDP 10 and DVDP 11. There is so much evidence of reworked Middle Miocene material that this author provisionally interprets the core interval from 35.43 m to 222.43 m as sediments scoured from ancient Miocene fjords during the uplift Of the Transantarctic Mountains.
So far, no Pliocene or Pleistocene diatoms have been found in the 38.43 −222.54 m interval. This suggests a Miocene age for the material even if it has been reworked. Fossil diatoms themselves indicate a Middle Miocene age with close affinities to the RISP J9 cores. No subdivision of this large interval has yet been found except there are some intervals barren of fossil material (148.63 - 167.17 m and 186.09 - 213.70 m).
The upper section 9.71 m - 21.70 m is different. Even though the majority of diatom fragments are similar to those in the lower core, non-marine diatoms occur. The analysis of DVDP 10 & 11 indicates that this flora is a Pleistocene to Early Pliocene flora which lived in terrestrial lakes, or in freshwater lakes wedged between ice shelves and the land, or in freshwater pools on ice shelf surfaces. As yet no definite date can be assigned to this upper section other than to indicate a Pleistocene - Pliocene age.
In August-September a fuller report will be available on the diatom stratigraphy of the MSSTS core. There are some intervals which may provide some control if the diatom fration can be concentrated by heavy liquid techniques.
ACROSS SOUND SURVEYS
Six lines approximately normal to the axis of McMurdo Sound were set out with flags on wooden beacons at 2 1/2 km spacing to facilitate surveys across the sound (Fig. 10). Ice breakout prevented those lines north of the Strand Moraines from extending more than 16 km east from the Victoria Land coast. It was intended to make extensive piston coring, bottom photography, bathymetric and gravity surveys. However, electronic problems with the triggering of the camera prevented any underwater photography and the piston coring was only partially successful.
Piston cores were obtained from 9 sites (Table 8). The corer, 1 m long by 47 mm in diameter, was loaded with 40 kg of lead. It was lowered on a 4 mm wire rope through a 25 cm diameter hole drilled in the sea ice by mechanical auger and triggered to free fall the last 5 m to the sea floor. Core was recovered in a plastic liner and held with a phosphorbronze cone core catcher, extended by plastic strips. Most cores obtained were less than 60 mm long and only one attempt in three produced any core at all. The reasons for non-recovery of core were not ascertained but it appears likely that when lowered rapidly the corer descends on a helical path induced by spinning due to unwinding of the hawser laid rope. In addition, there may have been core loss due to inadequate functioning of the core catcher.
Eleven piston core samples were examined. Most of the cores, (PC1-8) contain dominantly calcareous foraminiferal faunas, with several hundred well-preserved tests present. PC 9-11 contain dominantly finely agglutinated assemblages, and a lower number of tests. The preservation of calcareous tests in these three samples is very poor, indicating re-working or calcium carbonate dissolution.
Cores 4 and 5 consisted of live sponge and sponge spicule mat respectively. Core 4 had a sparse foraminiferal assemblage but species present were similar or identical to those in the other cores.
The sediment in the samples varies from very fine sand to granule and pebble size clasts. To date no sedimentologic analyses have been attempted on this material.
Bathymetric Data (BAS)
At all gravity and piston core sites in McMurdo Sound water depth was measured to an accuracy of 1 m with a weighted terylene line. Along the Strand profile, McMurdo Sound has an assymetric cross-section with the longer limb on the western side and a maximum water depth of 611 m occurring two thirds of the way across the sound. The Butter Point profile is similar. The Ferrar profile runs down the centre of the valley formerly occupied by the Ferrar Glacier. Water depths in the valley were found to vary between 200 and 235 m but 15 km from the present glacier snout there is an abrupt rise in the sea floor and water depth decreases to 125 m. Further out water depth increases again to 180 m, the typical depth obtained from many measurements throughout the New Harbour area. The shallows at the mouth of the Ferrar Valley are thus anomalous. They are thought to be due to moraines left by the retreating Ferrar Glacier. Similar moraines, now submerged, have been reported from elsewhere in McMurdo Sound (Northey & Sissons (1974); Wong & Christoffel, in press).page 29
|PC1||Drillsite||77 33.4||164 23||195.6|
|PC2||Drillsite||77 33.4||164 23||195.6|
|PC3||Drillsite||77 33.4||164 23||195.6|
|PC4||5 km west of Cape Armitage||77 51.7||164 40||139|
|PC5||5 km west of Cape Armitage||77 51.7||164 40||139|
|PC6||De Vries fish hut||77 52.3||164 30||456|
|PC7||2 km west of Cape Armitage|
|PC8||Beacon 2 strand||77 45.5||164 42.5||169|
|PC9||Ferrar Glacier Snout||77 41.7||163 31||236|
|PC10||Ferrar Glacier Snout||77 41.7||163 31||236|
|PC11||Stn 32 Ferrar Valley||77 41.3||163 42||230|
Reference Pole at the snout of Ferrar Glacier (BAS)
A 75 × 50 mm pole with 500 mm square crossed red plywood vanes was set up on the floating snout of Ferrar Glacier. The pole is buried about 1.5 m in the ice and the top of the pole was measured to be 0.860 m above the ice surface on 9.11.79.
- 77°41′ 30.3935″ South
- 163°31′ 15.3502″ East
- F1 77°43′ 09.2660″ South 163°32′ 05.7509″ East
- F2 77°42′ 52.9057″ 163°41′ 33.7723″
- F3 77°39′ 33.3433″ 163°31′ 39.0883″
Sea Ice Gravity Survey (BAS)
Gravity was observed with a Worden gravity meter at 2 1/2 km intervals along all profiles except that at Cape Armitage (Fig. 10). All observations on the sea ice were repeated and the standard error of observation found to be 0.4 mgals. The positions of stations were determined by starting profiles at known locations and setting a course directly toward another known feature. Distances were measured by metre wheel. Precise surveys were subsequently made of the entire Strand Profile and of three beacons in the Ferrar Profile including one at the snout of the Ferrar Glacier. In all cases station positions are known to better than ± 200 m. Elevations on the sea ice are known to within 0.1 m. The total error in computing Bouguer Anomalies is less than 0.7 mgals.
Bouguer Anomalies computed for a crustal density of 2.67 gm/cc and water density of 1.00gm/cc were used to construct Figure 10, a Bouguer Anomaly map of McMurdo Sound Dry Valley region. The map includes additional data from land based surveys discussed later (Event 13). Bouguer Anomaly profiles along the lines of observation are given in Figure 11. The main feature is steep positive eastward gradient across the Victoria Land Coast previously described by Bull (1962) and Smithson (1972). Smithson attributed his results to crustal thinning under McMurdo Sound together with a +0.2 gm/cc intrusion at a depth of 4 km in basement under the Sound.page 30
Our survey also shows a 15 mgal anomaly in the reverse sense to the main gradient and not found in the previous surveys. The anomaly has a wavelength of 5 km and is centred 10 km east of the Victoria Land Coast. Preliminary models show that it is consistent with a vertical 0.4 gm/cc density discontinuity having a throw of about 1 km and mid depth of about 1 km, the feature could be a basement fault down thrown to the east.
Figure 10 Preliminary Bouguer Anomaly Map of western McMurdo Sound with gravity and bathymetry profile lines shown.
BARRETT, P.J. 1979: Proposed drilling in McMurdo Sound - 1979. In Nagata, T. ed. Proceedings of Seminal: III on Dry Valley Drilling Project 1978. Memoirs of national Institute of Polar Research Special Issue 13. Tokyo p. 213-239.
BARRETT, P.J.; TREVES, S.B. 1976: Dry Valley Drilling Project Bulletin No. 7. Northern Illinois University. 126 p.
BARRETT, P.J.; FROGGATT, P.C. 1978: Densities porosities and Seismic velocities of some rocks from Victoria Land, Antarctica. N.Z. J. Geology Geophysics 21 (2): 175-87.
BARRETT, P.J.; BARRETT, P.J. 1979. MSSTS 1979 Scientific Operations Handbook. Antarctic Research Centre, Victoria University of Wellington 44pp.
BULL, C. 1962: Gravity observations in the Koetlitz Glacier area. Southern Victoria Land, Antarctica. N.Z.J. Geol. Geophys. 5: 810-19.
GOLTERMAN, H.L.; CLYMO, R.S.; OHNSTAD, M.A.M. 1978: Methods for physical and chemical analysis of fresh waters. 2nd ed. Blackwell. 210p.
HAYES, D.E.; FRAKES, L.A. 1975: Initial Reports of the Deep Sea Drilling Project, Vol. 28, U.S. Govt. Printing Office, Washington, 1120 p.
JENKINS, D.G. 1971. New Zealand Cenozoic Planktonic Foraminifera, N.Z. D.S.I.R., N.Z. G. S. Paleontological Bulletin 42, 278 p.
NORTHEY, D.J.; BROWN, C.; CHRISTOFFEL, D.A.; WONG, H.K.; BARRETT, P.J. 1975: A continuous seismic profiling survey in McMurdo Sound, Antarctica, 1975. Dry Valley Drilling Project bulletin no. 5: 167-179.
NORTHEY, D.J.; SISSONS, B.A. 1974: Preliminary seismic profiling survey in McMurdo Sound, Dry Valley Drilling Project Bulletin No. 3: 234-289.
SMITHSON, S.B. 1972: Gravity Interpretation in the Transantarctic Mountains near McMurdo Sound, Antarctica. Geol. Soc. of Amer. Bull. 83: 3437-3442.
WARD, B.L. 1979. Late Quaternary Foraminifera from Elevated Deposits of the Capes Royds-Barne Area, Ross Island, Antarctica, M.S. Thesis, Northern Illinois University, De Kalb, 229 p.
WRENN, J. H. 1977. Late Cenozoic subsurface micropaleontology, biostrati-graphy and general geology of Eastern Taylor Valley, Antarctica. M.S. Thesis, Northern Illinois University, De Kalb, 255 p.
WONG, K.; CHRISTOFFEL, D.A. In press. A reconnaissance seismic Survey of McMurdo Sound and Terra Nova Bay, Ross Sea, in McGinnis, L.D. (ed.). Results of the Dry Valley Drilling Project. American Geophysical Union Antarctic Research Series.
* Gas bubble from top of casing