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Victoria University Antarctic Research Expedition Science and Logistics Reports 1979-80: VUWAE 24

Triassic studies at Horseshoe Mountain (Barry Walker)

Triassic studies at Horseshoe Mountain (Barry Walker)

Five days were spent at Horseshoe Mountain, near Mt. Fleming, where geological mapping and sampling was carried out. The strata cropping out are the Feather Conglomerate (Late Permian-Early Triassic) and tile Lashly Formation (Mid-Late Triassic). (Plate XI)

The Feather Conglomerate is a corase to very coarse poorly sorted quartzose sandstone with large scale trough cross-bedding. The upper part is represented by a series of "fining-upward" cycles of medium, moderately well-sorted sandstone (Fleming Member - McKelvey et al., 1970).

The Lashly Formation is a sequence of sandstone and carbonaceous mudstone and has been divided into four members (Barrett et al., 1972); Members A, B and C appear to be complete at Horseshoe Mountain with member D occurring within the top 15 meters of the summit.

The Lashly Formation also crops out at the summit of Mount Fleming where 20–30 meters of member A is represented. Reconnaissance and a small amount of sampling of the Lashly Formation at Shapeless Mountain was all that time and weather conditions permitted. Several of the key stratigraphic horizons found at Horseshoe Mountain could be recognised at Shapeless Mountain, including the thin blue-grey muds-bone beds containing white rootlets and the silicified tree horizon.

Detailed petrological studies will be made of the sandstone samples from Horseshoe Mountain to determine mineralogical changes that may occur throughout this Triassic sequence. The relationship between sandstone texture and sedimentary structures will also be studies.

References

Barrett, P.J.; Grindley, G.W.; Webb, P.N., 1972. The Beacon Supergroup of East Antarctica. In Adie, R.J. (ed.), Antarctic Geology and Geophyics, Pp. 319-332.

McKelvey, B.C.; Webb, P.N.; Gorton, M.P.; Kohn, B.P., 1970. Stratigraphy of the Beacon Supergroup between the Olympus & Boomerang Ranges, Victoria Land, Antarctica. Nature 225, 1126-8.