IMMEDIATE SCIENCE REPORT
Event K042 Glacial History of the East Antarctic Ice Sheet at Allan Hills
Antarctica New Zealand 1999/2000
ANTARCTICA NEW ZEALAND REPORT NO 1: IMMEDIATE SCIENTIFIC REPORT
Note: this document reports on the activities of two coincident studies conducted under the K042 event. Where necessary for clarity, details and comments for the two studies will be presented separately.
1 Popular Summary of Scientific Work Achieved
This project is a detailed study of ancient glacial deposits termed the Sirius Group at Allan Hills, Southern Victoria Land, Antarctica. The Sirius Group is a collection of Neogene deposits that crop out at high elevations (mostly >1500 m) throughout the Transantarctic Mountains (TAM). Allan Hills occupies a low point in the TAM, making the site more susceptible to overriding by the EAIS during minor volume fluctuations. The aim of this project is to show whether the Sirius Group was deposited by valley glacier or continental ice sheet, by wet- or dry-based glacial ice, by a single depositional event or several overriding events and to determine paleoflow direction.
This past field season ran from mid-November 1999 to mid-January 2000 at Allan Hills during which time field mapping of early glacial deposits was continued from last season. The Sirius Group takes the form of seven patches of thin debris with a total area of 2 km2. From these, eight outcrops were selected for detailed description and sampling. The collected data include: orientations of 300 stones, 270 linear glacial abrasions and 90 planar deformational structures. In addition, 37 rock samples were collected for laboratory analysis. Sample processing has not yet begun but evidence indicates wet-based glacial deposition. Although the number of advances is not yet known, the work thus far suggests flow from the southwest and west. The presence of a cirque incised into a surface capped with Sirius deposits on the south side of Trudge Valley reveals a later phase of local temperate ice before the present cold ice sheet formed.
Univ. of Amsterdam
Research objectives that are of interest to the University of Amsterdam are three fold. Firstly, description and quantification of glacio-tectonised bedrock from 'Sirius' related glaciations. Research of these features further understanding into the character and form of previous glacial overriding in the Allan Hills nunatak, as well as provides indicators for paleo ice flow direction. Secondly, the collection of Sirius diamict samples for analysis using the technique micromorphology. Micromorphology has proved to be a useful tool in distinguishing between glacial diamicts of different origins world-wide. It is envisaged that micromorphology analysis of these Sirius samples will contribute towards understanding the character and regime of the Sirius glaciation(s). A bulk texture analysis sample was also taken in concert with every micromorphology sample. Thirdly, an objective that was only realised once in the field is the description and quantification of glacio-tectonised bedrock from a recent (non-Sirius) advance of the local Manhaul glacier. Furthermore, a diamict associated with these glacio-tectonised bedrock features was collected for micromorphology (and bulk texture) analysis so to provide an in situ investigation of the only non-Sirius glacial diamict found in the Allan Hills thus far.
Three spatially variable micromorphology samples taken from a discontinuous moraine linear ridge at Taylor glacier snout will provide hitherto unknown information on the microstructures of this deposition feature and help resolve the process(es) behind its formation and hence identity. Additional samples were removed from the compact debris-laden basal layer of Taylor glacier to allow in situ textural and structural analysis, by micromorphology, of this subglacial environment.
2 Proposed Programme
|1)||to complete geological mapping of the Sirius Group at Allan Hills begun during the 1998-1999 season|
|2)||to study deposits of the Sirius Group for the purpose of interpreting the nature of the ice that deposited it|
|3)||to select sites for drilling to be conducted during 2000-2001 season|
Univ. of Amsterdam
|1)||Build upon research carried out by Hiemstra and van der Meer (1999) in their field report for the Netherlands Centre for Geo-ecological research titled: Neogene Glacial History of the Allan Hills, South Victoria Land, Antarctica. This would include quantification of Sirius related glacio-tectonic bedrock deformation structures and further descriptions and sketches.|
|2)||Collect spatially and stratigraphically variable Sirius diamict samples for analyses by micromorphology. Wherever these micromorphology samples are taken, a small sample will also be taken for bulk texture analysis. Determine whether this is possible with a University of Amsterdam hand held drill or by simply removing a block of diamict using a chisel and geological hammer.|
|3)||Describe, sketch and quantify glacio-tectonic deformation of bedrock related to a recent advance of the Manhaul glacier. Collect spatially variable samples of Manhaul glacial diamict associated with the glacio-tectonic deformed bedrock for analysis by micromorphology. Wherever these micromorphology samples are taken, a small sample will also be taken for bulk texture analysis.|
|4)||Collect samples of 'sublimation till' from the snout of Taylor glacier and Suess glacier, Taylor Valley for analysis by micromorphology.|
|5)||Collect samples from the debris-laden basal layer of Taylor glacier itself for micromorphology analysis.|
|6)||Determine the practicality of undertaking pre-impregnation of unconsolidated sediments in the Antarctic field, with daily temperatures considerably below zero.|
3 Scientific Endeavours and Achievements
The study involved collaboration with Dr. Stephen Hicock, an associate professor at the University of Western Ontario in Canada. A concurrent study was done by Mark Lloyd-Davies, a Dutch student under the supervision of Dr. Jaap van der Meer based at the University of Amsterdam. Lloyd-Davies studied micro-scale subglacial deformational features of the Sirius Group at several sites including Allan Hills. Jeremy Mitchell conducted a study of ridge sets at Allan Hills for the purpose of determining their depositional agent(s).
The main focus of the work at Allan Hills was the investigation of Sirius Group deposits. The initial tasks in this continuing investigation were to conduct reconnaissance (recce) to familiarise ourselves with the area and then continue the mapping of Sirius distribution begun the previous season. During this time major outcrops were selected for later detailed investigation. These recces proved to be very fruitful as much was learned about the glacial deposits and they provided an opportunity to examine the variety of diamicts found in the area. As additional event members arrived, detailed studies of outcrops began and continued until the end of the season. Data collected from the outcrop and mapping work include the following: orientational measurements of 300 clasts and 90 deformational features in the Sirius Group at both measured outcrops and stop locations, recorded orientations on 270 abraded (striated) and faceted clasts throughout the study area, collected 37 rock samples for lab analysis.
Recent glacial deposits near the edge of the Manhaul Glacier discovered by Barrett and Atkins during the 1997-1998 field season were studied in more detail this season. This page break study was the focus of Atkins, while Barrett, Hicock and Holme contributed expertise as well. The study of these deposits was a major focus for van der Meer and Lloyd-Davies as they outline below. Glacial abrasions on bedrock and stone surfaces were documented and their orientations measured. These deposits occur as sparse patches of crushed and comminuted the underlying Beacon Supergroup. This work included delimiting the southern extent of the deposits in central Allan Hills using differentially corrected GPS. A benefit of mapping the distribution of these deposits was establishing their stratigraphic relationship to the Sirius Group.
Most fieldwork was conducted using standard geological field tools (eg. geological hammers, compasses, cameras) with the exception of a Trimble GPS rover unit to which we had access for three days. The GPS rover unit operated adequately in the cold conditions with shortened battery life being the only significant impact of the cold environment on the system.
Univ. of Amsterdam
From the Allan Hills 50 diamicts were collected for analysis by micromorphology. 10 of these are thought to be related to the advance of the Manhaul glacier, 32 to the Sirius glaciation(s) and the remaining 8 the author, at this stage, is unsure of. The 50 samples came from 40 different sites identified, all of which were triangulated, photographed and given a context description. A table appendix of samples collected can be provided upon request. Where appropriate glacio-tectonised bedrock fractures were quantified using strike and dip measurements. Some of the sites included those described by Hiemstra from field season 1998-1999 and others from sites logged and sampled in depth by Holme during field season 1999-2000.
22 sketches were drawn of glacio-tectonic bedrock deformation thought to be related to the advance of the Manhaul glacier. All the sites, representing variation in both spatial distribution and scales of deformation, were photographed and described with principle fractures quantified by strike and dip measurements.
Finally, in addition to the above, general notes related to observations on geomorphological processes occurring throughout the Allan Hills were taken, although these were on an ad hoc basis.
In terms of field methodology, the hand held drill transported from the University of Amsterdam proved ineffective in sampling Sirius glacial diamicts. However owed to the semi-lithified status of many of the Sirius glacial diamicts, the samples could be aptly sampled and orientated using a chisel and geological hammer. With practice this also became possible for the more unconsolidated diamict related to the Manhaul glacier advance.
A principal method developed was using a pre-impregnation technique for samples collected from both the Allan Hills and Taylor Valley. This pre-impregnation technique has been used before in the field, but never at temperatures considerably below zero or upon samples as unconsolidated as those collected in Taylor Valley. All pre-impregnation took place in the Allan Hills. It was found that the samples did pre-impregnate satisfactorily using a 50:50 mixture of acetone and varnish, the difference from the cold being that complete pre-impregnation took 3 to 4 days opposed to the usual 24 hours. Secondly, improvisation was used when pre-impregnating the very unconsolidated samples. Pieces of cardboard were cut out in the same dimensions as the samples, and elastic bands used to secure further the 'propping' action of the cardboard upon the samples. This was a crucial requirement when the supporting micromorphology tin was removed from the sample. All of the samples were labelled and orientated using a piece of paper placed upon their surface and once the samples had been pre-impregnated they were placed in a sample bag and wrapped in brown tape. The brown tape also had the sample name and orientations written on it, and the sample was then placed in bubble wrap and wrapped once again in brown tape. Lastly, the sample field number and orientations were labelled as beforehand. A combination of pre-impregnation and tight multi-layered wrapping insured that the unconsolidated samples maintained an in situ structure whilst in transit from the Allan Hills, south page break Victoria Land to the University of Amsterdam. Recent production of thin sections, in the University of Amsterdam, from these samples collected in Taylor Valley has yielded satisfactory results. This demonstrates that the method outlined above may be employed in temperatures experienced upon the Antarctic polar plateau during at least December and January.
In Taylor Valley the 90km long Taylor glacier is an easterly flowing outlet of the East Antarctic Ice Sheet. It originates at Taylor Dome and terminates at an elevation of 50-60 metres within the Dry Valleys of South Victoria Land, Antarctica. The first objective was to take 3 micromorphology samples from a discontinuous linear moraine ridge found around the snout of Taylor glacier, the most prominent being a linear ridge up to 7 metres high and over 20 metres in length at the north eastern snout of Taylor glacier1. Characteristic features of the moraine are a loosely packed matrix that it is composed of predominantly well sorted fines. This, coupled with the presence of interstitial permanent ice in the majority of the moraine, and the extremely cold and arid conditions of Taylor Valley, has lead many to conclude that the moraine ridges are composed of sublimation till.
Melt out has been thought to be an alternative explanation for the deposition of this 'till'. The two processes are closely related except that sublimation is the direct transformation of ice to vapour, rather than the transformation of ice to water.
It is intended that the micromorphology samples will yield hitherto unknown information on the microstructures of this diamict and help resolve the process(es) behind its formation and hence identity.
Finally, 5 samples were removed from the debris-laden basal layer of Taylor glacier for analysis by micromorphology. Regions of the ice bed interface in Taylor glacier have been estimated to be at pressure melting point, whilst other areas have temperatures approaching −20°C. The glacier contains a debris-laden basal layer, up to 5 m thick, comprising of laminated, dispersed and massive debris-laden ice. Clean glacier ice overlies this basal layer. Descriptions were made of both the debris-laden basal layer of Taylor glacier and Suess glacier so to provide a context setting for the micro-morphological samples taken. The in situ micromorphology samples taken from Taylor glacier will provide new information on the interaction of constituent sedimentary particles in the subglacial environment of a Dry Valley glacier.
4 Publications (planned)
Hiemstra, J.F., and van der Meer, J.J.M., Neogene Glacial History of the Allan Hills, Antarctica – Section Logs, ICG Report 99/3, 36 p.
Schluchter, C, and Tchudi, S., Surface age dates from Allan Hills (in prep).
Atkins, C.B., and Barrett, P.J., Allan Hills Project – field data from 1997-1999 (in prep for April 2000)
Paterson, M.C.H., Allan Hills Project – field data from 1998-1999 (in prep for April 2000)
Atkins, C.B., Barrett, P.J., et al. Striae and other features from a cold-based ice advance, Manhaul Glacier, Antarctica (in prep draft for March 2000).
Atkins, C.B., Holme, P.J., and Mitchell, J., Antarctic Data Series No 24, Holocene glacial data from 1999-00 (in prep for April 2000).
Holme, P.J., Antarctic Data Series No 25, Sirius data from 1999-00. (in prep for June 2000)
Mitchell, J., Antarctic Data Series No 23, Ridge sets from 1999-00. (in prep for August 2000)
Mitchell, J., et al., Gravel-capped ridges in a polar desert – observations and possible origin (in prep draft for August 2000).
We are grateful to Antarctica New Zealand and the Victoria University of Wellington for their funding of our research and to the staff of Scott Base for their logistical support.
Univ. of Amsterdam
Financial support for the Dutch contribution to research with K042 and K064, Antarctica is in the form of a grant from the 'Nederlandse Organisatie voor Wetenschappelijk Onderzoek' (NWO or Dutch Organisation for Scientific Research).
The kind hospitality, support and guidance provided by Sean Fitzsimons and his K064 team, from the University of Otago is also gratefully acknowledged. Furthermore useful discussion and ideas provided by Professor Peter Barrett and Mr Cliff Atkins of Victoria University of Wellington and Dr Stephen Hicock from the University of Western Ontario are thankfully acknowledged.
I would also like to gratefully acknowledge the support, aid and recommendations for research from Dr Jaap van der Meer, my supervisor, before and during the field season.
Finally, the academic, field and social environment provided by Mr Philip Holme and Mr Jeremy Mitchell both from the Victoria University of Wellington were invaluable in making such a long field season a successful, productive and enjoyable one.
1 An additional weekend also provided the opportunity to take 2 samples from a moraine ridge at the snout of Suess glacier.