Stromatolites are the oldest evidence for life on Earth, but modern living examples are rare and predominantly occur in shallow marine or (hyper-) saline lacustrine environments, subject to exotic physico-chemical conditions. Here we report the discovery of living freshwater stromatolites in cool-temperate karstic wetlands in the Giblin River catchment of the UNESCO-listed Tasmanian Wilderness World Heritage Area, Australia. These stromatolites colonize the slopes of karstic spring mounds which create mildly alkaline (pH of 7.0-7.9) enclaves within an otherwise uniformly acidic organosol terrain. The freshwater emerging from the springs is Ca-HCO3 dominated and water temperatures show no evidence of geothermal heating. Using 16 S rRNA gene clone library analysis we revealed that the bacterial community is dominated by Cyanobacteria, Alphaproteobacteria and an unusually high proportion of Chloroflexi, followed by Armatimonadetes and Planctomycetes, and is therefore unique compared to other living examples. Macroinvertebrates are sparse and snails in particular are disadvantaged by the development of debilitating accumulations of carbonate on their shells, corroborating evidence that stromatolites flourish under conditions where predation by metazoans is suppressed. Our findings constitute a novel habitat for stromatolites because cool-temperate freshwater wetlands are not a conventional stromatolite niche, suggesting that stromatolites may be more common than previously thought.
Uranium-thorium dating of speleothems from two caves in the Junee-Florentine karst, Tasmania, provides some age constraints for associated elastic sediments including coarse dolerite-rich fl uvial gravels, which underlie the three oldest dated speleothems. The results suggest minimum ages of 15 ± 5 ka,-325 ka and >350 ka (two daces) for the gravels, implying that they are considerably older than the early Last Glacial age suggested previously for some fl uvial gravels in other J unee-Florentine caves.
The practice of referring to certain morphologically karst-like phenomena as 'pseudokarst' is problematic, because it ignores basic principles of sound classification, logical naming conventions and accepted geomorphic classifications and terminology. These problems have compounded the difficulty in establishing an accepted classification of 'pseudokarst' types. The practice embodies a karst-centric perspective which should be avoided in favour of using conventional geomorphic terminology for non-karstic features. We illustrate this by providing existing conventional terms for many 'pseudokarst' types reported in the literature.
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