Victoria University Antarctic Research Expedition Science and Logistics Reports 1994-95: VUWAE 39
Popular Summary of Scientific Work Achieved
Popular Summary of Scientific Work Achieved
The Beacon sediments of East Antarctica were deposited over the Devonian to Triassic geological periods, from 400 to 200 million years ago. They show evidence of significant changes in climate over that time. Palaeomagnetic measurements on rocks having similar time spans, from Africa, Australia, India and South America, which were then also part of Gondwanaland, give conflicting results regarding the continental drift of that landmass. Many researchers have made palaeomagnetic measurements on Antarctic rocks, including those collected on our previous VUW Antarctic Expeditions in the 1978-79 and 1980-81 seasons. To date, all these have yielded a single pole, for a time 160 million years ago in the Jurassic period, corresponding to a massive intrusion of dolerite sills into the Beacon sediments. Heat and fluid from these intrusions largely destroyed the primary magnetisation acquired by rocks older than them. We have recently remeasured some rock samples from the VUW expeditions, using newly developed techniques. Some rock samples from Mt Crean, Portal Mountain and Alligator peak appear to have retained some primary magnetisation. However, insufficient unprocessed samples remained for us to obtain statistically acceptable results. It was thus necessary to obtain further samples from those promising sites in order to corroborate the measurements.
We obtained over 200 oriented cores, 25 mm in diameter and 50 to 150 mm long using a light portable drill specially adapted at VUW for Antarctic conditions. The sampling was carried out between 30 Nov and 6 Dec 1994 at Mt Crean, on the edge of the Polar plateau, 200 km west of Scott Base. The sediments sampled are red siltstones from the Aztec Group, of Upper Devonian age (approximately 350 million page 3 years ago). They were probably deposited in fresh water lakes and contain finely divided haematite which has the highest stability of any magnetic mineral.
Some preliminary measurements have been made on these samples. They give results similar to those of our remeasured samples. If confirmed by further measurements, it would mean that these rocks were deposited within 12° latitude of the equator. These results differ from those found from African and Australian rocks of similar age, A reassessment of the structure of Gondwanaland and its climate at the time will be necessary in the light of these new results.
Sampling and mapping the Sirius glacial moraines; the age of the Sirius Group glacial deposits in the Transantarctic Mountains has been the topic of considerable debate. The controversy centres on the source of the three million year old marine microfossil diatoms found in tillite beds in the glacial deposits. There are two conflicting models for the source of these microfossils. One is that the diatoms were from the antarctic interior and were subsequently eroded and deposited in the tillite. This implies extensive deglaciation and the existence of marine basins inland of the Transantarctic Mountains three million years ago. The second model is that the three million year old diatoms were blown by wind into the tillite, which could have been of much greater age (fourteen million years or more) and incorporated by periglacial processes. The aim of this project is to distinguish between these two models.
Two sites having Sirius deposits were surveyed and n series of rock sections was sampled at various depth intervals. Neighbouring snow samples were collected, melted, filtered and the residue collected to check for currently existing diatoms. The field work was carried out between the 18th and 30th November, 1994. The first site was at Table Mountain, 150 km west of Scott Base at an altitude of 1800 m on the south side of the Ferrar Glacier. The formation was draped for 2 km along the upper edge of the valley. The second site was at Mt Feather, on a bench at altitude 2500 m on the western edge of the Ferrar Glacier.
A contamination free laboratory has been prepared for processing the sediments to extract the diatoms. Experiments to find the most effective extraction method have been completed and the main extraction programme has commenced. Many diatoms have been found and meaningful interpretations will soon be possible.