IMMEDIATE SCIENTIFIC REPORT
K042: Styles of early glaciation near the margin of the East Antarctic Ice Sheet, South Victoria Land
Antarctica New Zealand 2000/01
1 Popular Summary of Scientific Work Achieved
This project is a detailed study of ancient glacial deposits termed the Sirius Group, focussed mainly at Allan Hills, but now including Mount Feather and Table Mountain, South Victoria Land (Figure 1). 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 East Antarctic Ice Sheet (EAIS) during minor volume fluctuations, while Mount Feather has the highest elevation deposits of the Sirius Group in the Dry Valley region; Table Mountain is nearby Mount Feather and of similar elevation to Allan Hills, but the deposits there are more varied. The aims of this project are 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. The expansion of the study this season to include deposits at Mount Feather and Table Mountain significantly widens the scope of the project and will permit a valid regional perspective.
The recent field season ran from mid-November 2000 to 22 December 2000 and included visits to the three field sites: Allan Hills, Mount Feather and Table Mountain. Holme and Hicock's work at Allan Hills consisted of outcrop description and mapping (continued from the 1999/2000 field season), while their work at Mount Feather and Table Mountain focussed on outcrop studies. In total, nine outcrops were studied and 24 samples were taken. Collected data include: 330 stone orientations, 51 linear glacial abrasions and 79 planar deformational structures. Bornholdt's B.Sc Honours project was to map and sample volcanogenic and sedimentary deposits that comprise Mt. Watters and its immediate vicinity. Additionally, Holme aided K047a in choosing potential sites for their drilling program at Allan Hills.
2 Proposed Programme
|1.||to study deposits of the Sirius Group for the purpose of interpreting the nature of ice responsible for its deposition|
|2.||to expand the scope and regional significance of the project by the inclusion of deposits at Mount Feather and Table Mountainpage 3|
|3.||to collaborate with K047a in drilling Sirius Group deposits at Allan Hills and Table Mountain|
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.
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.
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).
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
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.
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.
Goff, J., et al., Table Mountain, (submitted).
Atkins, C.B., and Barrett, P.J., Allan Hills Project - field data from 1997-1999 (in prep for 2001)page 6
Atkins, C.B., Barrett, P.J., et al. Striae and other features from a cold-based ice advance, Manhaul Glacier, Antarctica (??).
Atkins, C.B., Holme, P.J., and Mitchell, J., Antarctic Data Series No 24, Holocene glacial data from 1999-00 (??).
Holme, P.J., Antarctic Data Series No 25, Sirius data from 1999-00. (in prep for 2001)
Holme, Hicock, Barrett, Interpretation of subglacial dynamics and the thermal regime of the margin of the East Antarctic Ice Sheet during deposition of the Sirius Group at Allan Hills, South Victoria Land. (draft prepared by ??)
Holme, Barrett, Hicock, Dickinson, A synthesis of the Sirius Group at Allan Hills, Mount Feather and Table Mountain: the nature of the Sirius Group glacial event. (draft prepared by ??)
Hicock, Holme: A case study of the Sirius Group at Mt. Feather emphasising boulder pavements. Comparison with Wilson's drill hole study near east section. (draft for Sedimentary Geology prepared by ??)
Mitchell, J., Antarctic Data Series No 23, Ridge sets from 1999-00. (??)
Schluchter, C., and Tchudi, S., Cosmogenic exposure-age dates from Allan Hills (in prep).
We are grateful to Antarctica New Zealand and the staff of Scott Base for their logistical support and to the Victoria University of Wellington Science Faculty for funding this research.
Financial support for the Dutch contribution to research with K042 and K047a is in the form of a grant to Dr. Jaap van der Meer from the 'Nederlandse Organisatie voor Wetenschappelijk Onderzoek' (NWO or Dutch Organisation for Scientific Research).
Barrett, P.J., Bleakley, N.L., Dickinson, W.W., Hannah, M.J., and Harper, M.A., 1997, Distribution of Siliceous Microfossils on Mount Feather, Antarctica, and the Age of the Sirius Group: The Antarctic Region: Geological Evolution and Processes, p. 763- 770.
Bleakley, N.L., 1996, Geology of the Sirius Group at Mount Feather and Table Mountain, South Victoria Land, Antarctica, M.Sc. thesis, Victoria University of Wellington, 273 p.
Bruno, L.A., Baur, H., Graf, T., Schluchter, C., Signer, P., and Wieler, R., 1997, Dating of Sirius Group tillites in the Antarctic Dry Valleys with cosmogenic 3He and 21Ne: Earth and Planetary Science Letters, vol. 147, no. 1-4, p. 37-54.
Dickinson, W.W., ed., 1997, Field and Scientific Data Report: Sirius Group Study, Table Mountain, Antarctica, Nov-Dec 1996: Antarctic Data Series no. 19, Victoria University of Wellington, 98 p.
Wilson, G.S., Barron, J.A., eds., 1998, Mount Feather Sirius Group core workshop and collaborative sample analysis: BPRC Report no. 14, Byrd Polar Research Centre, The Ohio State University, Columbus, Ohio, 122 p.