Silurian pinnacle reefs of the Canadian Arctic

Silurian pinnacle reefs, the first described in the Canadian Arctic Archipelago, are exposed on Ellesmere and Devon islands. Two main reef trends occur, one of early middle Llandovery to middle Ludlow age and a second of middle Ludlow to Late Silurian or Early Devonian age. Reefs of both phases contain lime mudstone cores: some are stromatactoid-rich, and others consist predominantly of microbialite-rich lime mudstone or microbial boundstone. Facies sequences of both reef phases show evidence of upward-shallowing overall, but in the older reefs, isochronous capping facies are dominated either by coral-microbial boundstone, an unusual reef facies for the Silurian, or by stromatoporoid boundstone and floatstone. This difference perhaps reflects variation in wave stress and the apparent ability of a few corals thickly encrusted by, or associated with, microbial boundstone and skeletal algae to withstand greater wave energy than a stromatoporoid-coral-rich reef community.