Three Silurian bioherms of the Högklint Beds, Gotland

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Abstract
The Wenlockian Högklint Beds of Gotland represent a “barrier zone” of large bioherms and intervening channels. Three bioherms sampled north of Visby consist of 53% calcilutite matrix and represent quiet-water mud-mounds with organism stabilization but no skeletal framework or properties of wave resistance. The dominant organisms are stromatoporoids (35%), crinoids (18%), tabulate corals (15%) and calcareous algae (13%). Large colonies are less than 0.5 m in size, have relatively simple, massive growth forms and provide few special habitats for other organisms. In consequence, the bioherm-dwelling fauna consists of unspecialized mud-dwellers with the same diversity and taxonomic composition as co-eval, level-bottom communities. No ecologic succession is apparent within bioherms, and an upward change from stromatoporoid to algal dominance reflects a simple change in physical conditions.