Immediate report on the Victoria University of Wellington Antarctic Expedition 1959-60: VUWAE 3
Physiography and Glaciology
Owing to the restricted time that was available, no long-term glacial projects were attempted, but field observations were made whenever possible.
The Victoria Valley, formerly ice-filled is now free of ice for most of its 40-mile length. Remnants of the glacier system are now: The Lower Victoria Glacier, an invading tongue of the Wilson Piedmont, to the east; The Upper Victoria Glacier, flowing from a large ice-field to the north-west; and the Webb Glacier to the west. Bordering ranges reach an average height of 4500 feet and on these, hanging cirques and valleys show a general accordance of floor levels, These cirques often have remnants of ice on thier backwalls which commonly show small terminal moraines as evidence of recent wasting and retreat. No such evidence was seen at the snouts of major glaciers.page 7
The valley floors are mantled by thick moraine which rarely shows any glacial structures, but is invariably patterned by frost polygons. Although the moraine varies greatly in size and rock composition, no glacial striations were seen. Large areas of sand occur and well developed sand dunes are found to the north and east of Lake Vida. The effect of wind erosion was shown by a differential polishing on the faces of larger rocks, and quite frequently by fields of well-developed faceted pebbles.
The form and setting of Lake Vashka suggests it originated as a kettle- a deep remnant of ice left in the moraine by irregular glacial retreat. Large boulders and fine sandy bands now exposed on the surface of the lake ice support this theory. It is possible that the majority of the lakes on the valley floors originated in this way, and many may never have been entirely melted. Certainly the small lake at the head of Balham Valley and the empty depression at the junction of Balham and Barwick Valleys are of this form.
Stream beds leading into these lakes differ greatly, depending on the type of moraine on which they develop. The streams flowing westward from the Packard and Lower Victoria Glaciers over flat sandy floors have a braided course up to 100 yds. Wide. In contrast the western stream flowing into Lake Vashka is often 20 feet wide out cut 10 feet deep in coarse moraine. A great quantity of water would be required to develop a bed like this, although this summer only a trickle was running here and there. Along these streams in Barwick, Balham and Upper Victoria Valleys, well developed strings of paternoster lakes were found.
Basement rocks occur over almost the entire length of Victoria and Barwick Valleys. They are best exposed at the eastern end of the valley because the Ferrar Dolerites and overlying Beacon sediments obscure them toward the west.
The oldest rocks are the metamorphics of the Ross System, early Palaeozoic or Pre-Cambrian in age. These include graphitic marbles, schists, granulites and gneissic rocks, all with a constant trend of 280°.
At Lake Vida a salmon-pink or grey-coloured granite of the Admiralty Intrusives crosses the valley in a north-south direction, cutting the metamorphic rocks discordantly. Occasional pebbles of this granite are found in the basal Beacon sediments and it might be the major source rock of the sandstone.
Further eastward, the schists and gneisses are cut by a porphyritic granite which is well developed in the Purgatory Peak and Miller Glacier areas. Its ago and relationship to the 'Vida' granite art not certain, but laboratory study of specimens will help to determine this.
The basement rocks, of both Rosa system and Admiralty Intrusives, have been intruded by a wide variety of acid and basic dikes ranging in composition from aplites to pyroxenites. It is hoped that further study of these will give a relative ago for the members of the Admiralty Intrusives.
Beacon Group Sediments
Beacon sediments are restricted to the western half of the valley with the most easterly exposures occurring on peaks to the north of Lake Vida. Sequences of Beacon sandstone show a marked thickening toward the west, for while the most easterly outcrop was only 50 feet of basal sediments, a virtually continuous sequence of 3500 feet was examined west of the Webb Glacier. In one eastern section, onlap of near horizontal sediments onto a planed basement surface dipping at 12° west shows the area of sedimentation at that page 8 time was gradually extending towards the east.
Small variations in a generally uniform quartz sandstone mark off broad divisions of the sedimentary column. The lowest bed is a conglomerate layer which passes upwards into a cross-bedded quatrz sandstone with numerous worm tracks and abundant pyrites as scattered crystals or concretions. Overlying this are 500 feet of pure quartz sandstones with occasional beds showing mud-cracks and ripple-marks. Several coarse conglomerate layers up to 6 feet thick follow, marking the base of a 2500 feet thick coal-measure sequence of cross-bedded sandstones, felspathic grits and green-coloured siltstones. Numerous thin carbonaceous layers occur at intervals throughout this sequence, and occasional impure coal seams reach a maximum thickness of 3 feet.
Samples of fossil leaf and stem impressions from this sequence have not yet been studied, but they might give an age to the sediments which are at present loosely dated as ranging from Devonian to Jurassic. Shale and carbonaceous siltstones were sampled for pollen-analysis also. No results are yet available.
Intruding the basement and the Beacon group are near-horizontal sills of the Ferrar dolerites. A sill intruding the basement has a uniform thickness of about 800 feet, and dips westwards at 5°. The Beacon group is shattered and complexely intruded by a dolerite of different composition. This upper dolerite is at least 4-5000 feet thick, and the Beacon sediments can be considered as rafts floating within the dolerite. Bifurcation and complexity of intrusion of this upper sill increase towards the west.
Many specimens were collected for laboratory investigation.
No significant mineral discoveries were made, but some minor occurrences were noted.
Pyrite and Chalcapyrites: Minor amounts of these two copper minerals occur in orthoclase dikes west of the Packard Glacier.
Haematite: A minor occurrence of haematite was found north of Lake Vida. It is only a few square yards in area and of no importance.
Amethyst: At the base of the lower dolerite an impure variety of amethyst occurs in small veins. It is not of gem quality.
Coal: Thin impure seams of coal with a maximum thickness of 3 feet were found south of the Webb Glacier. It is of no importance.
Restricted areas of soil which occurs within the region were sampled and profiles were examined. Generally they show a cemented topsoil, with a dry friable subsoil above the permafrost level. In Balham Valley red, green, and mottled soils were found. Specimens await further examination and some data will probably be handed over to the Soil Bureau, D.S.I.R.
Observations, and some excavations, were made on permafrost phenomena. Relationships to the deposition of salts and the formation of soils were noted.
Evaporite salts forming in depressions were studied. Usually only a thin surface crust, one example near Lake Vashka had salts 30 inches thick and saline waters with a temperature of 20.5°F. The composition of salts awaits analysis, though the bulk is probably calcium sulphate.