The lateral relationships among the San Adrián, Canalón and Olaja members of the upper part of the Alba Fm. are discussed. These rocks are considered to be parts of a carbonate ramp developed from latest Viséan or early Pendleian to middle Arnsbergian times. The new name Millaró Beds is proposed herein for a thin interval of marine beds with middle-upper Arnsbergian ammonoids and conodonts, and laterally equivalent to part of the Olaja Mb. The Millaró Beds constitute the upper part of the Alba Fm. providing an additional criterion for the identification of the boundary between the Alba and Barcaliente formations at many sections across the Cantabrian Mountains. These beds represent sedimentation in a starved basin and a transgresive event at the beginning of the Variscan foredeep formation. This basin was subsequently filled by the siliciclastic rocks of the Cuevas Fm. and the marginal carbonates of the Barcaliente Fm.
The review of both published and new conodont data are applied to the recognition of different stages around the Mississippian/Pennsylvanian boundary. Finally, the distribution of conodont genera in the upper Arnsbergian to Kinderscoutian Barcaliente Fm is also given.Asturias (Comunidad Autónoma). Consejería de Educación y Cultura; PB2002-079Ministerio de Ciencia y Tecnología; BTE2002-03819Ministerio de Ciencia y Tecnología; BTE2003-01012Ministerio de Ciencia y Tecnología; BTE2003-0160
