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Immediate report of Victoria University of Wellington Antarctic Expedition 1989-90: VUWAE 34

THE HISTORY OF THE ROSS SEA REGION DURING BEACON TIMES (K047)

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THE HISTORY OF THE ROSS SEA REGION DURING BEACON TIMES (K047)

Abstract

Beacon sediments between Mt Metschel in the south and Robinson Peak in the north were examined during a 60 day, 950 km long traverse. Although a large number of days were lost to bad weather, most of the scientific alms were achieved.

The Pyramid Erosion Surface between Metschel Tillite and basal Welter Coal Measures was found to be at least locally conformable. This indicates that the retreating ice sheet was proximal to vegetated areas and that the time break believed to be associated with the erosion surface may be very small.

Observations suggest that the Beacon was deposited in an intracratonic sedimentary basin, no evidence was found to support the view that marine incursions occurred during Beacon times.

An extensive suite of samples were collected and will be used to provide a carbon/sulphur geochemical profile of the Beacon and to examine the effects of dolerite intrusions on the usefulness of carbon/sulphur as a paleoenvironmental indicator.

The lower part of the Lashly Formation was the object of a special study. Paleocurrent measurements and facies sequences recorded in Lashly A, suggest a deltaic, fluvio-lacustrine setting.

Proposed Programme

Work conducted by Victoria University and the Geological Survey in recent years has shown that both the Taylor and Victoria Group sediments in south Victoria Land have been deposited by non-marine processes (Sherwood et al 1989, Woolfe 1989. Woolfe et al 1989), in contrast to earlier interpretations of the Taylor Group using trace fossils (Bradshaw 1981).

During 1989-90 a four man Victoria University party visited exposures in the Skelton Névé to Robinson Peak area to took for facies, paleocurrent and thickness changes that may provide clues as to the mechanics of basin forming processes.

It has been suggested by some workers (Collinson et al 1987) that the Beacon Supergroup was deposited in a foreland basin, but this is not consistent with many features of the Beacon, including absence of deformation, basin symmetry, petrology of basal sediment and also the present day regional configuration of the Ross Sea sector.

Questions to be addressed by the current study include; where was the Beacon Basin in relation to the continental margin and what processes were driving basin development?

In addition to this regional study two local investigations were started during the summer, a comparison of the Pivot and Welter Coal Measures and a reinterpretation of Lashly A sediments. These projects are currently being undertaken as Masterate and BSc Honours programmes respectively. They also lead into more detailed studies of Beacon strata proposed for 1990-91 at Allen Hills.

This work will concentrate on modelling the processes that deposited upper Weiler Coal Measures, Feather Conglomerate and the Lashly Formation. This should provide a fluvial model that is better able than those of Allen (1965) and Smith (1989) to explain the occurrence of sheet sandstones in apparently meandering sequences.

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Scientific Endeavours and Achievements

Introduction

Exposures of Beacon Supergroup sediments between Mt Metschel and Robinson Peak were examined during a 60 day. 950 km traverse from Scott Base. Although a significant number of days were lost to bad weather while travelling on the Ross Ice Shelf these delays were almost certainty less than the weather, mechanical, weekend and public holiday delays we would have experienced with helicopter support.

Travel was generally easy, the only exception being on the Lower Staircase, where freak, deep soft snow conditions made travel extremely slow.

Facies descriptions with thicknesses along with paleocurrent data were obtained from a number of localities on Mt Metschel, Portal Mountain, Mt Cream, Pivot Peak, Mt Fleming, Mt Bastion and Robinson Peak. These observations provide valuable information on ancient paleoslope direction and basin subsidence.

Detailed descriptions of Pivot Coal Measures were made at Pivot Peak and these will be used to compare these Devonian sediments with the better understood and more widespread Permian Weiler Coal Measures. At the same time vertical and lateral sample suits were collected and these will be used to study the effects of Ferrar Dolerite on carbon sulphur ratios and to examine the suitability of carbon sulphur geochemistry as a paleosalinity indicator for Beacon Rocks.

Extensive paleocurrent and facies analysis was conducted on exposures of Lashly A, where fining upwards cycles are preserved with low sinuosity channels.

Results

Loaded channels of Maya Arkose in Metschel Tillite (diamictite phase) at Mt Crean show that the time represented by the Pyramid Erosion Surface is geologically insignificant. This supports previous observations which suggested a gradation between Metschel Tillite and Weiler Coal Measures at Mt Fleming (Pyne 1986).

A pebbly carbonaceous shale (diamictite) occurs on a ridge south of Mt Fleming. This unit is of limited extent but is clearly exposed below the base of the Maya Arkose. Initial interpretations are that the carbonaceous material is primary, suggesting a temperate climate at the time of deposition. It is hoped that samples may contain spores suitable for dating.

Preliminary results suggest that the lower part of the Lashly Formation (Lashly A) was deposited in a fluvio-lacustrine setting, possibly initially fed by a large braided river which deposited Feather Conglomerate higher up on the flood plain. At several locations the Lashly-Feather boundary Is gradational and at Horseshoe Mountain facies characteristic of the Feather Conglomerate are interbedded with typical Lashly sediments over a 20 m interval. The Lashly A-B boundary becomes difficult to place north of Mt Bastion.

Structures resembling HCS and SCS were observed along with logs and peat rafts in Lashly B at Horseshoe Mountain. These are similar to HCS and SCS observed last year at Allan Hills in the upper Weller Coal Measures and suggests that similar depositional processes were acting. We do not know what flow conditions produce these structures but it is hoped that a model for their formation will be developed after the proposed Allan Hills project in 1990-91.

Initial interpretations based on isopach data, support our view that the Beacon was deposited in a tectonically quiescent intracratonic basin of substantial size and duration.

Skolithos was observed in non-marine sediments at Pivot Peak and Horseshoe Mountain No evidence of marine incursion was found and we now believe that the entire Beacon Supergroup in South Victoria Land is non-marine.

Geochemical data, including the planned carbon/sulphur profile of the Beacon Supergroup is not yet available.

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Note: Since this report was prepared, geochemical data has revealed that the Pivot Coal Measures Member is non-carbonaceous. The black finely divided material is titano-magnetite and the name Pivot Member is proposed as an alternative (Amot and Woolfe in press).

Publications

The results of this field season will be written up as part of a PhD thesis (Woolfe) an MSc thesis (Amot) and a BSc (Hors) project (Zwartz). A paper reporting preliminary results of the carbon/sulphur geochemistry of the Beacon and the effects of dolerite intrusion is planned, as are papers on the regional tectonic setting, the Pyramid Erosion Surface and depositions! modelling of Lashly A.

Environmental Impact

All campsites were on snow. All non-burnable rubbish was returned to Scott Base, burnable rubbish was returned to Scott Base where possible, the rest was incinerated and the ashes returned to Scott Base. Human wastes were disposed of locally. A limited number of geological samples were collected for laboratory study in New Zealand.

Future Research

During 1990-91 we propose re-visiting Allan Hills, following a short visit in 1988-89. The programme at Allan Hills will concentrate on the fluvial processes that were occurring during Beacon Deposition. We aim to develop a model which is better able to explain the geometry and formation of fluvial sediments than existing models (Allan 1963, 1965, Smith 1989).

We intend to process data in the field using personal computers which we plan to house in a hut of some sort. As Allan Hills is a location visited frequently by both New Zealand and American parties the provision of a semi-permanent structure should be considered.

The only changes to the proposed programme for 1990-91 are likely to be in timing of personnel.

Discussions are continuing with the New Zealand Geological survey over the possible cooperative publication of a 1:25,000 geological map of Allan Hills.

Management of Science In the Ross Dependency

At our Event Briefing at Scott Base on Nov 5, we were fold that we needed to submit a full scientific proposal to RDRC for our "extension" to be approved and we would not permitted to visit areas which fell within this "extension" until approval have been received from RDRC.

After a number of phone calls to New Zealand the issue was resolved but several points resulting from this incident require further discussion.

1)Our proposed route was sent to Ant Div in March 1989, and was discussed fully at Tekapo. No changes were made to the proposed route and it was not clear to anyone on base exactly where it was we had extended to.
If there were a genuine problem why was it not picked up and sorted out earlier, at Tekapo for instance?
2)On arrival in Christchurch we were met at the Airport and briefed at the Harewood Store, from where we were told that we did not need to report to the Antarctic Division Office. Despite being delayed in Christchurch, no messages were left at the Windsor advising us to report to the office even though, 3 days before Christchurch sent a memo to Scott Base requiring us to submit a new proposal. It would seem reasonable to have contacted us in Christchurch, especially as the problem would have been much easier to solve while we were still in there.page 21
3)The first we heard of the affair was at Scott Base via "rumour control", and on asking if there were any problems we should know about we were told no! It was not until our Event Brief the next day, that the same person showed us the memo he had received from Christchurch 4 days earlier.
4)It does not seem reasonable that "sensitivities" between Woolfe and another Antarctic researcher, and shortage of time should be cited as reasons why the Event was not to proceed as approved at Tekapo.

Two members of the Event briefly entered restricted air space above the Barwick Valley SSSI. This occurred while being pulled out from Mt Bastion in bad weather, the helo crew had already spent a night on the mountain when a small clearing provided a flyable route through the Barwick. No landings were made.

Acknowledgements

Throughout the field season we experienced superb support from Scott Base Staff, their enthusiasm and dedication saw us get into the field ahead of time and once in the field their continued support was unprecedented. Several members of the Scott Base team deserve special mention, in particular we thank Doug Henderson and John Lee for their excellent work in the Stores Dept., the comms operators for keeping us amused on the many occasions when we were tent bound!, and Don Hammond for his unrelenting work, often long into the night.

We also thank Garth Varcoe and his team for establishing a fuel dump for us a Commonwealth Camp prior to our arrival, and Eric Saxby for assistance in planning the traverse.

Hovercraft support was provided by ANS and Helicopter support by VXE-6.

Finally, special mention must be made of our Antarctic Division field assistant, Tony Teeling. Tony's enthusiasm was unrelenting and he contributed significantly to the success to the programme.

References

Allen, J. R. L. 1963: The classification of cross-stratified units with notes on their origin. Sedimentology 2: 93-114

Allen, J. R. L. 1965: A review of the origin and characteristics of recent alluvial sediments. Sedimentology 5: 89-191

Bradshaw, M. A. 1981: Paleoenvironmental interpretations and systematics of Devonian Trace Fossils from the Taylor Group (lower Beacon Supergroup) Antarctica. New Zealand Journal of Geology and Geophysics 24: 615-652

Collinson, J. W.; Kemp, N. R.; Eggert, J. T. 1987: Comparison of the Triassic Gondwana sequences in the Transantarctic Mountains and Tasmania. In G. D. MacKenzie (ed), Papers and Proceedings of the sixth Gondwana Symposium.

Sherwood, A.M.; Kirk, P.A; Woolfe, K.J. 1989: Depositional setting of the Taylor Group in the Knobhead area; southern Victoria Land Antarctica. New Zealand Geological Survey Record 35: 122-125

Smith, N. D.; Cross, T. A.; Dufficy, J. P.; Clough, S. R. 1989: Anatomy of an avulsion. Sedimentology 36: 1-23

Woolfe, K.J. 1989: Beacon studies in southern Victoria Land 1988-89, Victoria University (K047). New Zealand Antarctic Record 9.2: 74-79

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Woolfe, K.J.; Kirk, P.A.; Sherwood, A.M. 1989: The geology of the Knobhead area, southern Victoria Land, Antarctica. Misc Map Series 19 1:50,000 Map and Notes. NZDSIR Wellington.