Late Visean/early Namurian conodont succession from the Esla area of the Cantabrian Mountains, Spain

Conodont fauna recovered from pelagic nodular limestone sequence exposed near Santa Olaja de la Varga precisely dates the upper part of the Alba Formation in the Esla area of the Cantabrian Mountains. In terms of goniatite stratigraphy, the formation ranges into the early Namurian E2 interval which has been identified by the occurrence of the conodont Gnathodus bollandensis . The investigated conodont fauna includes exclusively deep-water forms and is dominated by species of Gnathodus and Lochriea . The former genus is represented primarily by the bilineatus lineage, in which a new species Gnathodus cantabricus sp. nov. has been recognized and is described herein. Representatives of the another gnathodontid girtyi lineage,generally present in the late Visean/early Namurian deep-water faunas, are extremely rare. The vertical succession of Lohriea species is closely comparable to those recognized in Northern England, Poland and Ukraine. The Visean/Namurian boundary is thus placed at the first occurrence of Lochriea cruciformis , 4.7 m below the top of the Alba Formation.