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Victoria University Antarctic Research Expedition Science and Logistics Reports 2000-01: VUWAE 45

3 Scientific Endeavours and Achievements

3 Scientific Endeavours and Achievements

This Event is a collaboration of researchers from Holland (Dr. Jaap van der Meer), Canada (Dr. Stephen Hicock) and New Zealand (Prof. Peter Barrett). The research proposal for the season's work initially included two PhD students (Holme and a Dutch student) and Hicock, but the Dutch student (Mark Lloyd-Davies) was forced to miss this field season because of a physical injury suffered in the weeks before the season was to begin.

The study of the Sirius Group at Allan Hills (Figure 2) began during the 1997-1998 season as a collaboration between Swiss and New Zealand researchers, but subsequently developed into the current configuration. The purpose of the research is to investigate glacial deposits termed the Sirius Group at three sites in the TAM. Initially the study was to be conducted only at Allan Hills, but through integration with the K047a event it became possible to study equivalent deposits at Mount Feather and Table Mountain for a minimum additional cost, thereby greatly increasing the scope of the project. A smaller study of deposits forming Mt. Watters, Allan Hills was conducted by Bornholdt for an Honour's project.

Figure 2. Allan Hills showing camp and locations mentioned in text.

Figure 2. Allan Hills showing camp and locations mentioned in text.

For Hicock and Holme, the focus of work at Allan Hills was to finalise their field investigation of Sirius Group deposits. Following last season's near-completion of mapping, the tasks this year were to finish the mapping, describe additional outcrops, gather additional data (eg. a sampling transect) in Trudge Valley - an area of particular interest to the investigators in reconstructing the glacial history at Allan Hills (Figure 3). The main mapping goal was to conduct a reconnaissance of the eastern limb of Allan Hills to search for additional outcrops of the Sirius Group. Unfortunately plans for the venture had to be dropped because Hicock was delayed
Figure 3. Trudge Valley, Allan Hills.

Figure 3. Trudge Valley, Allan Hills.

page 4 for too long at Scott Base and it was necessary to devote his shortened visit to outcrop work. The use of GPS gear to collect high precision points for use in a computer-based reconstruction of the paleo-landscape was unsuccessful because internal batteries in the GPS units failed. Although useful, the data is not crucial to the reconstruction, which will be pursued anyway.

While at Allan Hills Bornholdt mapped and sampled volcanogenic and sedimentary deposits that comprise Mt. Waiters to determine the nature of the feature and the eruptive event which produced it. His collected data include: samples collected for thin-sectioning and microprobe analysis, geological descriptions, and measurements of fracture and inter-unit orientations. He produced a geological map of Mt. Watters in the field.

At Mount Feather and Table Mountain Holme and Hicock focussed on investigations of Sirius Group outcrops while Bornholdt assisted. Deposits at Mount Feather were studied because they are the highest elevation occurrence of Sirius Group deposits in the Dry Valleys region and have been the focus of several previous investigations (eg. Bleakley (1996), Barrett et al. (1997), Bruno et al. (1997) and Wilson and Barron (1998)) (Figure 4). During the six days spent at Mount Feather, three outcrops were described and sampled. From analysis of the detailed data collected it is apparent even at this preliminary stage that the paleo-iceflow direction was not from the northwest, as proposed by Wilson and Barron (1998), but from the southeast.

Figure 4. Fieldsite at Mt. Feather showing outcrop locations.

Figure 4. Fieldsite at Mt. Feather showing outcrop locations.

The deposits at Table Mountain were chosen for investigation because they occur at a similar elevation to those at Allan Hills, but are sedimentologically more variable; previous investigations there include: (eg. Bleakley (1996) and Dickinson (1997)). During the eight days spent at Table Mountain, four outcrops were described and sampled (Figure 5).

Figure 5. Fieldsite at Table Mountain showing outcrop locations.

Figure 5. Fieldsite at Table Mountain showing outcrop locations.

From Allan Hills, Mt. Feather and Table Mountain, a total of nine outcrops were described and sampled this season. The data collected include: 24 samples taken for thin-sectioning and laboratory analysis, 330 clast orientations, 51 linear glacial abrasions (eg. Figure 6) and 79 planar deformational structures

Figure 6. Glacially abraded boulder at Mt. Feather. Note: paleoice-flow direction is from right to left.

Figure 6. Glacially abraded boulder at Mt. Feather. Note: paleoice-flow direction is from right to left.

page 5

Methodology:

Fieldwork was conducted using standard geological field tools (eg. geological hammers, compasses, cameras). No special actions or modifications were necessary for coping in the cold environment.

Summary of contributions by Hicock

Allan Hills: (Figure 2).

a)A ledge on Weller sandstone was discovered immediately northwest of "Boulder Ridge", which had impressive striae, grooves, rat tails, chattermarks (within grooves), and nail head striae caused by a southward advance of the Manhaul glacier at some time after deposition of the Sirius Group. These erosional features are associated with immature diamict and suggest that, at this place, the Manhaul was not cold based. A future Master's thesis could be done mapping the diamict and erosional evidence of the Manhaul, Odell, and other glacial lobes issuing from the main East Antarctic Ice Sheet. Surface exposure dating of stones in the diamict would be useful to reconstruct the timing of these post-Sirius glacial events. Sandstone boulder dispersal trains in Trudge Valley by the Manhaul Glacier, and quartzite by the Odell Glacier, further attest to the dynamic behaviour under those glaciers.
b)The ridge under the Odell glacier that parallels Trudge Valley may have been formed by the Odell overriding the dolerite dyke that crosses the valley at that place. Subsequently, the Odell may have dumped and streamlined sediment on the lee side of the dyke - the ridge could be a 'crag-and-tail' feature.
c)The ridges on the "Triangle" resemble recessional (ribbed) moraines.
d)Abundant roches moutonnees were discovered on the sides and bottoms of the SE gully, and adjacent gully to the northwest where Bornholdt worked. These are cirque basins that had local ice flowing downhill into Trudge valley.

Mt. Feather: (Figure 4)

Two boulder pavements were discovered in Sirius diamictite at the outcrop on the eastern corner of the Sirius Group plateau. Data collected imply that lodgement was the main process in pavement formation. Ice flow appears to have been across the bench of Sirius, roughly perpendicular to modern Ferrar glacier flow on the southeast side of Feather. Beneath the pavements is a dark grey comminution tillite that directly overlies Weller interbedded shale and coal which were overridden, deformed, and reconstituted to form the tillite.

Table Mountain: (Figure 5)

The southern edge of the Sirius platform resembles the distal side of a lateral moraine which could explain why it is the southern limit of Sirius at Table Mountain. It may mark the edge of an outlet glacier (ancestral Ferrar or Tedrow) that issued from the East Antarctic Ice Sheet to the southwest, sweeping eastward around an intrusive knob and over the north slope of Table.

Below TM-1 (Dickinson 1997) is a basin carved into Terra Cotta siltstone with Sirius exposed in its north side (not drilled in 1996 but studied by James Goff). This appears to be an old cirque, complete with recessional moraines resting on its floor and even over its northern edge. It could be that the ancestral outlet glacier overrode or pushed against the cirque glacier which prevented the deposition of Sirius in the basin proper.