| Summary: | Invasive tufa deposits on Foel Fawr, South Wales are forming from lime kiln waste deposited from the 18th century until the 1950s. The tufa deposits are unusual in their anthropogenic origin and form the largest site of this type in the UK. At emergence pH is extreme (>11) and this consequently generates significant pressure on organisms living in and around the system. Morphologically, the calcium carbonate tufa deposits are similar to those formed in other extreme environments (e.g. hot springs, caves), forming many of the same features (e.g. terraces, rimpools, pisoids, stalactites). By identifying and mapping tufa facies at Foel Fawr, the spatial distribution of these facies has been directly compared to these potentially analogous environments. Analysis of the fabrics associated with each facies highlights the importance of physico-chemical precipitation in the system; proximal facies are dominated by abiotic fabrics, while distal and marginal facies show an increasing degree of biological influence. This process is comparable to the partitioning of fabrics and facies observed in hot spring systems, however, the role of microbes in precipitation is apparently less important on Foel Fawr. The present day extreme chemistry of the site selectively excludes organisms and generates a partitioning of biology. Hydrochemical monitoring of the site reveals that the extreme pH of the system is in decline. The recession of the extreme hydrochemistry is confirmed by colonisation of previously excluded organisms and allowed the physical decay of the site. Fabrics preserved within the deposits support the suggestion that the extreme environments were previously much more widespread.
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