Cephalopod limestone biofacies in the Silurian of the Carnic Alps, Austria

Cephalopod limestones represent one of the most peculiar biofacies that developed in Silurian times along the northern margin of Gondwana. The presence and relative abundance of fossils, clearly visible in the field, enabled a taxonomic study of the main fossil groups since the end of the eighteenth century. Together with the most evident cephalopods, also bivalves, brachiopods and trilobites were studied in detail in different times. A good stratigraphic assignment either with graptolites or with conodonts was made of most sections. Paleoecological studies, on the contrary, were not so definite. Cephalopod limestones from North Gondwana are often referred to as a single unit, andthe same paleoecologic-environmental conclusions driven in an area are borrowed and extended to other regions. Key-stratigraphic sections (Rauchkofel Boden, Cellon, Rauchkofel Boden torl, Valentin Törl, Seewarte, Seekopf) representing distinctive paleogeographic/paleoenvironmental settings were taken into consideration and studied in detail in this work, paying particular attention to observe taphonomical information (abundance, dimension, orientation, colour, preservation, etc.) of all organisms composing the fauna. The study aimed to fit even the Carnic Alps cephalopod limestone biofacies into a more general picture of the Silurian. In particular, a precise depositional environment and an improved sequence-stratigraphical frame for the Silurian of the Carnic Alps in Austria based on a sedimentological, lithostratigraphical, biostratigraphical and microfacial approach was achieved (Brett et al., in press).Furthermore, analysis of “ooidal pockets” and “stromatolite-like” structures within the Pt. celloni – Pt. a. amorphognathoides conodont zones is also discussed with regard to their paleoenvironmental implications. Similar studies in other sectors (Oggiano & Mameli, 2006 from the Ordovician/Silurian of northern Sardinia), for this stratigraphical interval highlight that knowledge to date regarding these peculiar carbonate facies is still quitelimited. In-depth studies in key areas to recognise these markers may shed light on the relative positions of microterranes along the North Gondwana margin.REFERENCESBRETT C., FERRETTI A., HISTON K., SCHÖNLAUB H.P. Silurian Sequence Stratigraphy of the Carnic Alps, Austria. Palaeogeography, Palaeoclimatology, Palaeoecology (in press).OGGIANO G., MAMELI P. (2006). Diamictite and oolitic ironstones, a sedimentary association at Ordovician–Silurian transition in the north Gondwana margin: New evidence from the inner nappe of Sardinia Variscides (Italy). Gondwana Research, 9: 500-511.