Permian coal measures at Mount Bastion and Mount Fleming (Alex Pyne)

At Mt Bastion sedimentary strata of the Victoria group (Beacon Supergroup) and the intruding dolerite were mapped to aid the paleomagnetic and metamorphism studies. In the area mapped the strata is generally flat-lying and intruded by terminating and climbing sills, although in the area at the head of Gibson Spur immediately to the south the dip of the Beacon strata approaches the vertical.

Two detailed sections were measured from the Weller Coal Measures, here 200 m thick into the Feather Conglomerate. A point of considerable interest is the discovery of fossil soils (Plate XX) preserved in a sequence of silty beds forming the gradational contact between the Weller Coal Measures and overlying Feather Conglomerate. Soil horizons are extremely rare in any of the Permian coal measures of the Southern Hemisphere. Similar horizons were found in the same stratigraphic position at Mt Fleming.

The Beacon Supergroup and the intruding Ferrar Dolerite were also mapped at Mt Fleming (Plate XXIII) and Horseshoe Mt., and three laterally related sections of the Weller Coal Measures were measured in detail. The Beacon strata at Mt Fleming extend from the upper Beacon Heights Orthoquartzite (Late Devonian) to the Lashly Formation (Late Triassic). They are in part monoclinally folded and probably faulted also, in contrast to most other areas in south Victoria Land where there is scarcely a hint of tectonism. Careful mapping showed that the vertical displacement (throw) across the faulted monocline was about 230 m. The detailed study of the Weller Coal Measures begun this season will be used to determine a depositional model for the coal measures. Initial work this year has shown that in the lower and upper parts alternating coarse feldspathic sandstone and shale-coal horizons have resulted from channel and overbank deposition (Plate XXII) The middle part, predominantly medium to fine sandstone, is of channel deposits containing silicified-calcified logs and stumps in growth position (Plate XXI). This indicates exposure of channel bars for periods of time up to two hundred years.