Late Katian (Late Ordovician) carbonate mudmounds in the Turesø Formation, Peary Land, North Greenland, succeed normal marine faunas dominated by brachiopods, bryozoans, cephalopod and gastropod molluscs, aulaceratid stromatoporoids, corals and receptaculitid algae, in the Børglum River Formation, and are themselves succeeded by organic-rich, largely barren limestones. This peri-Laurentian succession suggests deteriorating environmental conditions from a normal marine to a more restricted basin during the Late Katian and Hirnantian, against a background of gradual marine regression following the peak of the Boda Warming Event. The generally low-energy depositional setting probably lay within the Inter-Tropical Convergence Zone on the equator.