Early Silurian conodonts from the Cantabrian Zone, NW Spain

Abstract

Extensive black shale formations occur throughout most of the Lower Silurian in SW Europe. However, a wider array of facies and the presence of stratigraphic gaps in the interval covered by the Ordovician/Silurian transition, make for complications in the stratigraphic succession. Directely underlying the Silurian graptolitic black shales of the Formigoso Formation, two small intervals of carbonate rocks occur in certain localities. These are the Viodo Member of the Castro Formation, formally defined here, and the upper part of the Getino beds, both dated here for the first time. Eleven limestone samples from the Viodo Member, and one dolostone sample from the Getino beds, have yielded a relatively abundant conodont fauna of low diversity, which can be referred to the A. petila and A. fluegeli Zones, respectively. By comparison with faunas from North Greenland and the Canadian Rocky Mountains, Rhuddanian to Aeronian ages seem to be present.