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ABSTRACT. The term “Waulsortian�? was introduced in 1863 for a particular assemblage of limestones in the Lower Carboniferous of Belgium. In 1883 it was given the status of a stage, ranking equally with Tournaisian and Visean. Within five years, this was shown to be invalid because the Waulsortian limestones demonstrably passed laterally into rocks of upper Tournaisian and lower Visean age. Thereafter, “Waulsortian�? has been used as a facies term, extending internationally as limestones of closely similar age and character have been discovered outside Belgium. In Belgium, the massive Waulsortian limestones were originally interpreted as reefs, rich in stromatoporoids and bryozoans. However, by the early 20th century the so-called stromatoporoids were shown to be sparry precipitates, and the “reefs�? were acknowledged to be unlike modern organic reefs in several important respects. Since that time, the interpretation has evolved so that Waulsortian limestones are now regarded as carbonate mud-mounds characterised by microbially mediated muds. The mounds were colonised by a range of organisms indicating growth in marine environments extending from depths of several hundred metres to relatively shallow, photic waters.
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