File: D030778.jpg
Microkarren are more extensive than suggested by earlier reports (Jennings, 1981, 1982; Dunkerley, 1983). The microkarren are most common on the flatter surfaces, especially on the gently rounded 'clints' of the pediments but also on the sides of the towers. However, I found microrills and other forms on slopes up to 60 degrees. Some microkarren are superimposed on rillenkarren or rain pits; these appear to be secondary features modifying the initial coarser form. Linear microrills grade to networks of irregular, discontinuous ridges and then to isolated, rasp-like, teeth.
I measured the following size ranges from a set of enlarged photographs: the microrills range from 0.2 to 2.8 mm wide, averaging 1.1mm; the micro-teeth were spaced 0.5 to 3mm apart, averaging 1.5mm. Vertical relief is generally less than 1mm; some rills are extremely shallow and visible mainly by a slight discolouration of the crests. Circular micro-pits also occur as small as 1mm across, but show a greater size range and all gradations up to normal rain pits (10mm or greater) can occur on one outcrop.
There is also fine micro-etching of structures such as irregular cracks, the crystal boundaries of the marbles, or the skeletal structure of fossil corals.
These small features have been under-reported because of their cryptic nature. They are most visible in areas lacking the ubiquitous thin grey algal coating, e.g. in the bare areas used by Wallabies. However, they seem too extensive to be a consequence of corrosion by Wallaby urine, as suggested by Jennings (1981, 1982). Solution by thin films of water, dew or light rain, seems the most likely origin ?
Jennings, J.N., 1981: Morphoclimatic control - a tale of piss and wind or the case of the baby out with the bathwater? Proc. 8th Int. Congress Speleology. 1: 367-8.
Jennings, J.N., 1982: Karst of northeastern Queensland reconsidered. Tower Karst, Chillagoe Caving Club, Occasional Paper, 4, 13-52.
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Micri-rills and networks, on a flat pediment. File: D030778.jpg |
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Micro-karren (rasp-like teeth and some pits), on a gentle slope. File: D030779.jpg |
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Micro-karren: rills and network. In a very shallow hollow on a pediment. File: D030716.jpg |
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Etched polygonal cracks with micro-teeth. File: D030752.jpg |
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Micro-rills on a marble pediment. Note coarse crystals. File: D030676.jpg |
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Micro-karren (rills and teeth) on a 15 ° slope. File: D030391.jpg |
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"rain" pits in lines and clusters. extensive micro-rills. File: D030755.jpg |
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Rillenkarren with Micro-karren (etchings and teeth). File: D030373.jpg |
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A clint with shallow "rain-pits" and rillenkarren. Plus superimposed micro-rills. File: D030682.jpg |
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Rillenkarren and a few "rain-pits". Plus Micro-karren (rills, teeth and pits). File: D030754.jpg |
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Rillenkarren modified by micro-rills. On a 25° slope. File: D030757.jpg |
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Rillenkarren grading down to a smooth 60° slope. Micro-rills occur within some rillenkarren. File: D030685.jpg |
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Rillenkarren grading down to micro-rills. On a clint. Stereopair - view cross-eyed. File: D030684.jpg and D030683.jpg |
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Fine micro-karren grade down to larger pits and then to rillenkarren. The upper (brown) part is near-vertical and sheltered by an overhang. Slope below is less steep. Stereopair - view cross-eyed. File: D030701.jpg |
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Micro-karren with secondary corraloid deposits. On a steep, sheltered, slope. This is a close-up of the central part of photos D030701 & ..702. File: D030703.jpg |
(c) KG. Grimes, 2003