Simple discoidal impressions are the only evidence for complex life in some Ediacaran and older rocks, but their interpretation is notoriously difficult. A puzzling discoidal form from the c. 560 Ma upper Burway Formation of the Ediacaran Longmyndian Supergroup, Shropshire, UK, is here reassessed. The structures, previously described as Intrites punctatus Fedonkin, are found on both bed tops and soles, and vary in morphology from mounds with central depressions to incomplete rings and pairs of short ridges. Examination in cross-section of the purported Intrites documented from the Longmyndian reveals a torus-shaped structure bounded by microbial mat layers and commonly containing white laminae. We interpret the “Longmyndian Intrites” as a product of microbial trapping, sediment binding, and authigenic clay mineral and carbonate precipitation on the flanks of small sediment volcanoes. Subsidence of the ring-like structure into muddy sediment results in a torus-shaped microstromatolite.
