IMMEDIATE SCIENCE REPORT
K047 : FLUVIAL AND PALEOBOTANICAL STUDIES AT ALLAN HILLS
New Zealand Antractic Research Programme 1990/91
Antarctica New Zealand December 1990 - Jan 1991
NZARP REPORT No. 1 : IMMEDIATE SCIENTIFIC REPORT TO THE ROSS DEPENDENCY RESEARCH COMMITTEE
During the 1990-91 field season three geologists from Victoria University's Beacon studies project revisited Allan Hills, an area where Beacon Supergroup sediments are exceptionally well exposed. The party also included a paleoclimatologist from the University of Adelaide and a sedimentologist from the University of Illinois.
The project was extremely successful, meeting all of its original objectives and discovering unexpected geological features. A 1:20,000 geological map was completed to draft stage, as was an accompanying text. A remarkable Permian fossil forest was documented and samples collected for paleoclimate studies. About 10,000 anchient river flow directions were measured, which along with lithologic observations have provided the basis for a more realistic model to explain the presence of sandstone sheets in meandering river complexes. Evidence was found of glaciers still existing in highlands to the east of Allan Hills during the period that the forest flourished. New field data suggest a previously unrecorded glaciation in Early to Mid-Jurassic times.
Allan Hills exposures are far more significant than originally anticipated. The Weller Coal Measures are superbly exposed and contain abundant fossil trees many in upright position. In addition the area contains the only known occurrence of large fossil trees in the Feather Conglomerate. These and other features have led to a proposal that part of Allan Hills be managed as a Specially Protected Area.
2) PROPOSED PROGRAMME
|a)||Resolve the apparently enigmatic occupance of sheet sandstones in a meandering river sequence observed during the 1988-89 field season (Woolfe 1989*)|
|b)||To determine the process responsible for the formation of hummocky cross stratification and swaley cross stratification in a nonmarine regime.|
|c)||To document and sample for paleoclimatic studies the extensively exposed Permian high-latitude forest.|
|d)||To produce a 1:20,000 scale geological map of Allan Hills and an accompanying text.|
3) SCIENTIFIC ENDEAVOURS AND ACHIEVEMENTS
The 1990-91 Beacon Studies project received excellent support from Scott Base and no logistic problems were encountered. In contrast to previous seasons the project experienced good weather conditions resulting in considerably more science being undertaken than was originally anticipated. The use of an Apple Hut at Allan Hills provided a warm and comfortable base for map drawing and computing. The inclusion of two overseas scientists in the party provided valuable additional expertise in specialist fields.
These factors combined with a strong team identity resulted in a very successful field season. All of our original objectives were achieved and a number of additional problems were addressed.
Field mapping at a scale of 1:20,000 was completed as planned. The Weller Coal Measures being mapped to member level. A draft map and text was completed in the field, and it is expected that this will be submitted for publication later this year (woolfe et al. in prep). Additional geographical control was established using a total station and three GPS sites established by the USGS-DOSLI program. Three cairns were established near the head of Manhaul Bay and tied into the GPS network. Details of these sites will be included in a volume of geological data to be published later this year.
Enigmatic Sandstone Geometries
Field relationships and paleocurrent analysis has shown that the apparently enigmatic sandstone geometries resulted from the interaction of two different sedimentary systems. Some of the sheetlike geometries probably represent episodic advances of a sandy alluvial fan originating in highland to the east while other originated within the meandering system itself.
This interpretation leads to two significant findings. Firstly, paleocurrent analysis of the fan derived sheets show that highlands of crystalline basement rocks existed to the East of Allan Hills during the Permian. Of more significance is the finding that meandering rivers can deposit extensive sandstone sheets with internally complex geometries and diverse paleocurrent directions. This contrasts strongly with accepted models of meandering river deposition and suggests that a previously unrecognised process was occurring.
Further work is required to fully document an alternative model. However, it is envisaged that the sheet sandstones were deposited by blind swamp-draining meandering rivers. The unusual bed geometry results from biogenic aggradation of the flood plain (swamp) exceeding the clastic accumulation of the meandering system (Woolfe et al submitted).
Paleobotanical studies revealed evidence for the in situ formation of Gondwana Coals a previously unrecognised feature (Francis et al. accepted). This evidence included the presence of Vertebraria roots in shaly units both within and at the base of major coal seams and the occurrence of upright stumps within coal seams.
Further laboratory studies are required to document fully the climate record contained in the fossil wood, but the occurrence of outsized clasts, ice needle impressions and a striated boulder in associated strata suggest that the climate was at least cold enough for the formation of winter ice locally, and perminent ice fields with glaciers higher in the drainage basin. Wide growth rings in the trees indicate that conditions were favourable during the growing season.
Hummocky and Swaley Cross Stratification
Paleocurrent determinations, facies associations and geometric considerations show that many of the structures resembling HCS and SCS within the Weller Coal Measures are drape features. Where pre-existing channel floor topography has been mantled by planar or ripple laminated sediment deposited in waning flood stage. It is believed that drape features of this type have not been previously documented.
|a)||Rhythmically laminated muddy sandstone and sandy mudstone. Rhythmic lamination is unusual in fluvial systems other that those controlled by seasonal ice melting.page break|
|b)||Pockets of outsized clasts, these are typically pebbles 2-5cm in diameter contained within sandy or muddy horizons. These grouped pebbles are interpreted as having been ice rafted by lake or glacier ice floating down current during of after major thaws.|
|c)||A large striated boulder was found in WCl in "Camp Valley". Multidirectional striae show that the boulder was striated prior to its inclusion in the surrounding sediment and the fine preservation suggests limited fluvial transport.|
An extensive suite of paleocurrent measurements (about 10,000) were made during the field season. Primary data processing was conducted in the field using at Toshiba T1600 laptop and a tailor made software package (PC 0.1, Zwartz in prep).
Further processing of this data base is required. However, initial results indicate that the relationships between ripples, crossbeds, bar sets, paleochannel directions and sinuosity are probably more complex than previously thought. It is anticipated that the data set will allow, possibly for the first time, a quantative analysis of preservation potential and bias within a meandering river complex. The entire data set will be made available in published form later this year (Woolfe (ed) in prep).
|a)||An extensive erosion surface (Mawson Erosion Surface (Woolfe et al in prep)) which page break separates Beacon and Ferrar rocks at Allan Hills. This surface has over 400 m of sharp relief at Allan Hills and indicates a period of uplift and erosion prior to the main magmatic phase of the Ferrar event.|
Mawson A is directly underlain by locally intensely folded sediments of the Beacon Supergroup. The intensity of folding decreases downwards from the erosion surface over a few tens of metres. Within the zone of most intense folding, metre and decametre scale isoclinal folds have formed during complex brittle failure of interbedded sandstone and shale while cataclastic flow occurred in some coal seams. Strain is partitioned into a zone subparallel with the Mawson Erosion Surface.
The style and distribution of deformation is closely analogous to that observed locally beneath the Sirius Formation, a known glacial deposit. This suggests that both the sub-Mawson and sub-Sirius strain resulted from similar processes. We believe that the deformation resulted from ice contact drag folding at the base of a dry-based glacier.
|c)||Several striated clasts were found within Mawson A. It is unlikely that these could have survived prolonged transportation and they are taken as direct evidence that diamictite and the sub-erosion surface deformation were glacially produced.|
Extensive exposures of the Sirius Formation occur through Allan Hills. Although the formation was not studied in detail during the 1990-91 a number of features were recorded which could form the basis of a more detailed study in the future.
|a)||Glacial striae are preserved in several locations both adjacent to and beneath the Sirius Formation. These could be used to supplement geomorphic and fabric studies in order to constrain paleo-ice flow directions.page break|
|b)||At a number of localities Sirius Formation directly overlies well exposed deformed Beacon sediments. It is believed that these underlying rocks were deformed by ice contact drag folding. A study of the structural styles of both the sub-Sirius and sub-Mawson deformed zone could provide a better understanding of ice-rock interactions.|
|c)||Several different emplacement mechanisms are suggested by the geomorphic position of the diamictite exposures. These include valley floor, valley wall and ridge line deposits.|
The expedition is expected to result in a number of journal publications, conference papers and an addition to the Victoria University Antarctic Data Series. The status of those publications on which work has already started is as follows:
Francis, J. E.; Woolfe, K. J.; Amot, M. J.; Barrett, P. J. : Permian fossil forests and climates of Allan Hills, Antarctica. 8th International Gondwana Symposium, Hobart.
Barrett, P. J.; Smith, N. D.; Woolfe, K. J. : Early Permian glaciation in Antarctica - Evidence from Allan Hills. 6th International Symposium on Antarctic Earth Sciences, Tokyo.
Woolfe, K. J.;0 Amot, M. J.; Barrett, P. J.; Francis, J. E. : Contrasting fluvial styles in the Weller Coal Measures at Allan Hills. 6th International Symposium on Antarctic Earth Sciences, Tokyo.page break
Woolfe, K. J. (ed) : Geological data from an ancient alluvial system (Permian) preserved at Allan Hills. Antarctic Data Series . Victoria University of Wellington
Woolfe, K. J.; Amot, M. J.; Francis, J. E; Barrett, P. J. : Geology of Allan Hills, southern Victoria Land Antarctica.
Papers on (with principle author(S)):
Jurassic Glaciation (Francis and Woolfe)
Paleocurrent signatures and preservation bias (Woolfe and Barrett)
Sheet Sandstone facies relationships and interpretation (Smith).
Paleoclimate from tree ring studies (Francis)
Non-avulsive Meandering systems (Woolfe)
5) ENVIRONMENTAL IMPACT
All non-burnable solid wastes (including human) were returned to Scott Base. Burnable solids were incinerated in the field and the remains returned to Scott Base for disposal.
A limited number of geological samples were collected for laboratory study. These were mainly for paleobotanical and paleoclimatology studies at the University of Leeds (Francis).
Three large rock cairns were established at survey control points near the head of Manhaul Bay. A number of small numbered cairns were established on significant outcrops however, these are expected to be dismantled by the wind.page break
Numerous refuge items left by previous expeditions were recovered and returned to Scott Base for disposal.
6) FUTURE RESEARCH
The 1990-91 field season was the last in the current round of Beacon studies at Victoria University. However, it is clear that further research should be carried out The excellent exposure and preservation of geological features in the Beacon Supergroup at Allan Hills makes the area ideal for the study of fluvial process. Many exposures documented by this and previous projects should be revisited in order to further our understanding of geological processes.
A number of findings made by the 1990-91 expedition will almost certainly result in further work being undertaken both in Antarctica and elsewhere.
|a)||Fluvial modelling is expected to produce a new model to explain the deposition of sediment by meandering rivers. Funding has already been secured for additional fieldwork in south Westland and it is anticipated that additional Antarctic field work will be proposed in the next few years.|
|b)||New evidence relating to Gondwana glaciation is likely to generate substantial international interest It is likely that a proposal to revisit Allan Hills to further investigate Jurassic glaciation, Permian glacio-fluvial interactions and glacially produced bedrock deformation will be prepared.|
|c)||Paleobotanical studies have revealed an unequalled occurrance of high-latitude Permian trees. It is almost certain that additional climatological and botanical studies will be conducted at Allan Hills considering the international significance of the occupance.|
In general it is felt that the next round of Beacon studies at Victoria University will involve additional interaction with overseas institutions and will be process orientated. However, although several overseas parties have expressed an interest in working with the universities Beacon program no definite plans for future work have been formulated.
7) MANAGEMENT OF SCIENCE IN THE ROSS DEPENDENCY
|a)||Abundant trees and logs within the Weller Coal measures. Excellent exposure combined with an abundance of both upright and fall trees makes this locality one of the best fossil Permian forests yet discovered. This is a unique and valuable occurrence containing a well preserved high-latitude flora.|
|b)||Fossil trees and peat rafts in the Feather Conglomerate. This represents the only known occupance well preserved fossil plant material in the Feather Conglomerate, a formation that spans the Permian-Triassic boundary.|
|c)||Excellent exposure of fluvial sediments. Natural processes of wind and glacial erosion have given rise to unequalled exposures of fluvial sediments (Weller Coal Measures).|
It is well known that fossil wood is easily collected from Allan Hills. This has led to its collection by scientists and other visitors (including helicopter crews, DVs and the like), and pedestrian traffic has dislodged and dispersed other specimens. These activities have already led to some destruction of irreplaceable and scientifically important specimens. We believe that a management plan needs to be introduced to protect these occurrences from further damage. We therefore formally propose that a Specially Protected Area be established at Allan Hills in due course.page break
- The permanent ice edge of Manhaul Bay from Denes Point to the western side of fiestmantle Valley.
- The ridge line from Denes Point to Balance Peak and Roscollyn Tor.
- A line drawn between Roscollyn Tor and Watters Peak.
- A line drawn between Watters Peak and Baldrick (GPS site marked by rock cairn on summit).
- A line drawn from Baldrick to the edge of the Permanent ice on the western side of Fiestmanle Valley.
- That entry into this area be restricted to protect the geological features contained within it.
- That the sampling of in situ fossil wood, leaves and other plant material should be permitted only after adequate scientific justification has been provided.
- That every effort should be made not to disturb fossil localities, and that pedestrian traffic should where possible be restricted to areas protected by surfacial deposits (moraine, scree, pavement) or snow.
- That the collecting of any fossil plant materials, in situ or otherwise, for other than scientific study should not be permitted.
The success of the 1990-91 field season is a reflection of the efforts and support of numerous people and organisations to all of whom we are grateful. DSIR Antarctic staff provided excellent support and advice in the planning stages and the efforts of Garth Varcoe in coordinating the Hut and staging equipment at Cape Roberts warrant special mention.
As usual support from Scott Base staff exceed all reasonable expectations and this was particularly true in the stores department. The USGS-DOSLI survey assistance team are thanked for siting two GPS site within easy walking distance of our campsite. These provided much need control for local surveying carried out during the project.
Alex Pyne (Expedition Manager at VUW) provided much logistic and computing advise during the planning phase of the expedition, and Dan Zwartz (VUW) wrote the paleocurrent software.
Funding for the expedition was provided by the New Zealand Vice Chancellors Committee, Victoria University's Internal Grants Committee and the Australian Geographic Society. The Internal Grants Committee (VUW) also provided funding to develop the software package.