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Abstract:

Solutional landforms have been described for over a hundred years from limestone terrains and are termed karst. In many tropical regions landforms of similar morphology but on highly siliceous sandstones and quartzites have also recently been identified. The similarity of many of these features in morphology and also in genetic solutional processes to those on limestone has prompted recent calls for these quartzose landforms to also be regarded as true karst.
Although not unknown in temperate latitudes, these highly siliceous solutional landforms have been most commonly studied in present-day tropical regions, or areas believed to have been tropical in the recent past. This concentration of research in hot-wet areas, allied with the long held assertion of the insolubility of silica, especially quartz, led to a belief that tropical climatic conditions are necessary for karstic solution of these rocks. However, some of these quartzose solutional landforms are known in areas of temperate climate where there is little evidence for prior tropical conditions. A comprehensive worldwide review of these landforms, and the processes involved in their formation, has not previously been conducted and forms the basis from which this study stems.
The Sydney Basin in southeastern Australia has had a stable temperate climate for much of the Cainozoic with no evidence of tropical climate. The highly quartzose Permo-Triassic sandstones of this area have little carbonate, but nevertheless display a wide range of landforms morphologically similar to those both on limestones and also tropical quartzites These include large bedrock towers, grikes, caves, smaller solution basins and runnels, and even widespread silica speleothems. This study describes the morphology of this suite of landforms in detail, and provides a comparative analysis of these sandstone forms to those reported from quartzites of tropical areas and also their limestone analogues. Various microscopic and natural water chemistry analysis are then utilised in examining the poorly understood natural processes responsible for their formation. The process of sandstone solutional weathering in the Sydney Basin is also compared with that reported from the tropics, finding very little difference in either the form or magnitude of attack between these two climatically distinct regions. No previous studies have examined the wide range of solutional features found on quartz sandstones in one region of a climate comparable to Sydney, nor the processes involved in the genesis of these forms.