Conodont faunas across the mid-Carboniferous boundary from the Barcaliente Formation at La Lastra (Palentian Zone, Cantabrian Mountains, northwest Spain); geological setting, sedimentological characters and faunal descriptions

Two different tectono-stratigraphic domains are recognised in the Cantabrian Mountains, Asturian-Leonese (Cantabrian Zone) and Palentian (Palentian Zone). The area under investigation belongs to the southern part of the Palentian Domain and attention is focused on the Upper Viséan to lowermost Bashkirian limestones at the village of La Lastra in northern Palencia. A new geological map of the Palentian Zone is accompanied by a more detailed map centred on La Lastra. The Barcaliente Limestone Formation (Serpukhovian to lowermost Bashkirian) occurs in the overturned limb of a recumbent anticline which constitutes the head of a south-verging major thrust unit, the Carrionas Thrust Sheet (Palentian Zone). It shows here a shallowing trend in the Serpukhovian. After a transgressive phase near the mid-Carboniferous boundary, the lower Bashkirian again shows shallowing culminating in a palaeokarst at the base of the overlying Perapertú Formation. The conodont faunas present a continuous succession across the Mississipian-Pennsylvanian boundary, most similar to the ones found at Aksu (Hissar Range, Uzbekistan).