The Cygnet Coal Measures is a unit of carbonaceous shale,
coal and feldspathic sandstone in Tasmania of
Upper Permian age. It is overlain
gradationally or disconformably by the Springs
Sandstone, the lower member of which, Barnetts
Sandstone, is a thinly-bedded, fine-grained feldspathic
to arkosic sandstone, and the upper, the
Mountain Lodge Sandstone and a more thickly-bedded,
medium-grained protoquartzite. The upper part
of the Springs Sandstone is probably Otoceratan.
The Permo-Triassic boundary lies within these
gradational non-marine units and cannot yet be
fixed accurately. The base of the Mountain Lodge
Member is probably the most convenient boundary
to use as the Permo-Triassic boundary in local field
mapping
