Ferruginous biolaminations within the pre-Hirnantian (Late Ordovician) of the Carnic Alps, Austria

Well preserved laminated structures occur within the Upper Ordovician of the Cellon section in the Carnic Alps (Austria), a world-famous reference section for Silurian conodont biostratigraphy. Microfacies from the Upper Ordovician Uqua Formation were characterised by using optical and scanning electron microscopy (SEM), an environmental scanning electron microscopy coupled with microanalyses (SEM/ESEM-EDX) and a confocal laser Raman microscopy. Ferruginous laminated structures overgrowing specific skeletal fragments occur in the lower part of the studied unit in the form of finely red-to greenish coatings composed of chamosite and goethite alternating with calcite bands. Laminae have arborescent to dendrolitic morphologies. Such morphologies suggest a biomediated genesis and the existence of a potential microbial factory acting in a nearby location from which coated material was later redeposited. These ferruginous coatings around organisms are not documented within the latest Ordovician Plöcken Formation at Cellon or in the coeval Wolayer Formation elsewhere.