Bryozoan?rich stromatolites (bryostromatolites) from the Silurian of Gotland and their relation to climate?related perturbations of the global carbon cycle

Bryozoan–stromatolite associations (bryostromatolites) formed conspicuous reef structures throughout the Sheinwoodian (Wenlock) to Ludfordian (Ludlow) stratigraphy on Gotland but have not been described so far. They are mainly composed of encrusting bryozoans forming a complex intergrowth with porostromate and spongiostromate microbes different from abundant stromatoporoid–coral–algal reefs respect their composition. In bryostromatolite growth stages can be identified. The observed succession taken as evidence for cyclic environmental changes during formation. Stenohaline reef-dwelling organisms, such echinoderms, sponges, corals trilobites, indicate fully marine salinities. Ten localities exposing bryostromatolites were discovered. Individual small few decimetres up one metre in size, occur solely shallow areas. Common features these cauliflower-like growth, high bryozoan diversity, abundance phosphatic fossils components pearls inarticulate brachiopods, enhanced bioerosion, Palaeomicrocodium crusts, vadose silt gypsum pseudomorphs. Palaeomicrocodium, well alternation other crust-forming contributors, suggest that it could directly at palaeo-sea surface, probably times minor high-frequency sea-level fluctuations. Vadose pseudomorphs after cavities subaerial exposure shortly growth. amount indicates nutrient input, by dust. All strongly elevated ?13C values. unusual combination sedimentological palaeoecological features, occurrence exclusively strong positive excursions, development responded climatic/oceanographic changes, which may played an important role control.