LA-ICP-MS U–Pb dating of Carboniferous ash layers in the Cantabrian Zone (N Spain): stratigraphic implications

Seven centimetre-thick volcanic ash-fall layers interbedded within the thick Carboniferous successions of the Cantabrian Zone in northern Spain were dated by U–Pb zircon laser ablation inductively coupled plasma mass spectrometry across an interval ranging from Visean to Kasimovian, thus covering most of the Carboniferous period. All these ash layers occur in fossiliferous successions, allowing us to insert the radiometric data within a well-constrained biostratigraphic framework. Considering the analytical uncertainty, the obtained ages match the ages inferred from the conodont biostratigraphy established in the Mississippian succession (which hosts the oldest two ash layers, Visean in age), and the fusuline and megaand microflora data from the strata hosting the Moscovian and Kasimovian (Westphalian–Stephanian) tonsteins. The age of a Langsettian tonstein along with data provided by several papers stating that in the Cantabrian Zone Langsettian floras were contemporaneous with lowermost Moscovian fusulines suggest that Langsettian floras could have been younger in Spain than in other areas. Our absolute ages provide new constraints not only for the correlation of the Carboniferous successions of the Cantabrian Zone with time-equivalent reference successions in other parts of the world but also for calibrating the Carboniferous global chronostratigraphic units based on marine fossils with the West European regional units.