The possible macrofossil Telemarkites enigmaticus from the Mesoproterozoic Gjuve Formation, Telemark supracrustals, southern Norway, was described by Dons in 1959. We here present finds of similar, but larger structures from the somewhat older Åmot Formation (c. 1150–1250 Ma). The elongated, strongly oriented, nodular structures are up to 25 cm long with a carbonate-rich core, and occur in metasandstones of probable lacustrine origin. The structures and surrounding rocks have been studied with a number of techniques, including XRD, XRF, petrographic thinsections, SEM-EDS, X-ray and CT imaging, hyperspectral imaging, anisotropy of magnetic susceptibility, stable isotope analysis (δ13C and δ18O) and palynological preparation. Convoluted and domed beds could represent metamorphosed microbialites, deriving from algal or bacterial mats. The nodular structures remain enigmatic, but may represent oncoids, desiccation features (rollup structures), early diagenetic concretions shaped by groundwater flow, or macrofossils of unknown biological affinity. The structure Telemarkites giganticus Gyøry, Hammer, Jorde, Nakrem, Swajda & Domeier sp. nov. is formally described.