TITLE:
Pan Gnammas (Weathering Pits) across Australia: Morphology in Response to Formative Processes
AUTHORS:
Brian V. Timms
KEYWORDS:
Corrosion, Water Layer Weathering, Laminations, Visors
JOURNAL NAME:
International Journal of Geosciences,
Vol.12 No.10,
October
27,
2021
ABSTRACT: Pan gnammas occur across Australia, mainly in granites and sandstones.
Their morphology and origins on Eyre Peninsula, South Australia are known, but
this Twidale model is not applicable everywhere. I investigated their
morphology and theorized on their origins at eight sites across the continent,
noting particularly their edge profiles, floors and depths in relation to their
geological placement. The steep sides, flat floors, depths up to about 25 cm in
laminated granites apply only in the hot climates of Western Australia and South Australia.
Laminations are rare in Victorian granites, so their pan gnammas have sloped
edges and are not as deep (ca. 10 cm)
and in the granitic uplands of southeast Queensland, corrosion at the edge is concentrated to a narrow zone and most gnammas are only ca. 5 cm deep.
Gnammas in horizontal sandstones in New South Wales and Queensland have steep
or sloping edges and reach ca 10 cm deep but in dipping sandstones of the
Grampians, Victoria horizontality of corrosion has produced visors at pan
edges. The vertically bedded Uluru sandstones have enabled
deeper corrosion and pans of different morphology. Regional depth variation has
biological consequences.