Seven localities yielding Microcodium are described from the Carboniferous and Permian of the Yukon Territory, Axel Heiberg, and Ellesmere. The Microcodium is generally perforating. However, microbreccias and reworked fragments containing Microcodium indicate that this enigmatic taxon was already present in Late Paleozoic time. Microcodium is therefore not necessarily the result of pedogenic Cenozoic alteration of older sediments. Cenozoic inorganic, bacterial, or pedogenic origins are improbable. An algal affinity is more plausible.