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

[Permian coal measures at Mount Fleming and Shapeless Mountain]

The Mt. Fleming area was revisited to complete a study of the Weller Coal Measures initiated the previous 1978-79 season. Further outcrops of the coal measures in the "cirque basin" at Mt. Fleming were measured and described in detail. These latest data complete the detailed three dimensional coverage of the outcrops which is required to determine the depositional history of the Weller Coal Measures. The new information has also helped to confirm and refine the interpretation of several features found the previous season.

In southern Victoria Land the alluvial Weller Coal Measures are deposited on the Pyramid Erosion Surface (P.E.S.) overlying the Permian Metschel Tillite. Barrett and Kyle (1975) has already shown from evidence at Mt. Fleming that the "time gap" represented by the Pyramid Erosion Surface is small. Work this year has shown that a pod comprising tillite interbedded with carbonaceous shale (Plate IX) is stratigraphically equivalent to a thin laterally extensive sandstone bed containing dispersed clasts and carbonaceous material. These three lithologies are considered facies of the Metschel Tillite. In some places the pyramid Erosion Surface has formed on the sandstone bed. In others, however, sandstone of the Metshcel Tillite appears to grade into the lowest shale lenses of the Weller Goal Measures.

At Mt. Fleming the Metschel Tillite facies are interpreted to have been deposited in glacial and proglacial environments. Small fluctuations of the ice front incorporated vegetation growing around the ice margin. The basal Weller Coal Measures were deposited immediately after the final ice retreat in a periglacial climate. The lithofacies association suggests deposition from a meandering stream system and this will be checked from analysis of the paleocurrent measurements taken from the coal measures. This will show more precisely the directions of current flow and the sinuosity of the depositing river. The paleocurrent directions from the outcrops at Mt. Fleming also will be compared with the directions from Shapeless Mt. 20 km away where the coal measures are very similar.

Three thin calcareous beds (av 100 mm) previously described by Barrett & Webb (1973) and Bradshaw (in press) were traced over a large area of Mt. Fleming this season. The trace of the outcrop delineates an area of about 10 square kilometres. Three very similar calcareous beds were also found in the same stratigraphic position at Shapeless Mtn. about 20 km away. It is inferred that the depositional environment in which these beds accumulated coexisted at both localities and that the environment was laterally continuous over 20 km.

Bradshaw (in press) has found analcime zeolite associated with the upper calcareous bed at Mt. Fleming and interpreted the analcime to have formed from evaporation. This season symmetrical ripple marks (Plate X) were found in the same bed (Bradshaws main horizon) and indicate subaqueous accumulation.

By determining whether the ripples are wave or current formed it is hoped to define precisely the depositional environment.

A point of interest last season was the finding of paleosols at Mt. Bastion and Mt. Fleming that appeared to have formed under cool temperate conditions in the Permian. This season similar paleosols were found higher in the sequence in the upper part of the Feather Conglomerate at Horseshoe Mtn. A comparison of the paleosols shows that both have a well-developed gammate structure in the greenish clay-rich upper horizon and an iron accumulation zone in the lower clay-deficient horizon.

The paleosols are interpreted to have formed under similar climates yet the nature of the flood plans on which they developed were quite different.