This is the fourth part of the series of rock texture pictures from Tenby. All so far have been from South Beach where the Carboniferous strata range from Hunts Bay Oolite, to High Tor Limestone, to Caswell May Mudstones, and Gully Oolite. Many of these close-up images have shown erosion patterns, caused sometimes biologically and sometimes chemically, or a combination of both. The first four photographs in this post show the fine, and approximately-linear ridges and grooves (click the pictures to enlarge them for a better view), that seem to be restricted to the otherwise smoother, un-pitted, darker patches on the surface of the rock. I am thinking that whereas the pits are probably caused by various effects of bio-erosion or bio-erosion plus solution, the almost microscopic grooves here could be the result of chemical erosion which sometimes occurs from contact with acid rain. If so, these micro grooves and ridges are microrills, and like miniature rillenkarren – a feature of karst topography – and they are evidence for relatively recent erosional activity.
The patterns of grooves and fissures in the four images below, could also be a karstic type of solution feature. I am not sure – but they are certainly intriguing and look to my eye rather like the tough wrinkled hides of elephant or rhinoceros.
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