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Victoria University Antarctic Research Expedition Science and Logistics Reports 1999-2000: VUWAE 44

Univ. of Amsterdam

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.