Ooidal ironstones and laminated ferruginous deposits from the Silurian of the Carnic Alps, Austria

Distinct ooidal horizons and diverse laminated ferruginous structures are reported from the Silurian of the Carinthian Carnic Alps. The former were recovered in forms of centimetric horizons at the base of a single section (Rauchkofel Boden). The Carnic Alps reports are the only record in the Silurian from the European sector of the Northern Gondwana margin. Ooids consist mostly of chamosite, goethite and mixtures thereof with subordinate amounts of apatite. Laminated ferruginous deposits are present in themajority of the investigated sections and are represented either by rare “stromatolite-like” structures or by abundant banded iron-rich fossil coatings, mostly around trilobites and cephalopods. Both types are composed of calcareous laminae alternating with layers rich in iron silicates or oxides (chamosite, goethite, and magnetite). All these deposits can tentatively be regarded as microbial. Magnetite coatings revealed peculiar filaments of possible organic nature, closely resembling fungal hyphae.