Pan Gnammas (Weathering Pits) across Australia: Morphology in Response to Formative Processes

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 appl y 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 ha ve enabled deeper corrosion and pans of different morphology. Regional depth variation has biological consequences.